One of Neptune's largest moons has stuck around the neighborhood much longer than scientists previously thought — in fact, it may be the sole survivor of the planet's earliest days.

Nereid, Neptune's third-largest moon, is probably the only moon left over from when the ice giant formed early in the solar system's 4.5 billion-year history, a new analysis of James Webb Space Telescope (JWST) data suggests.

The results, published Wednesday (May 20) in the journal Science Advances, contradict the previous story about Nereid's history told in the decades since its 1949 discovery: that Neptune "captured" the 220-mile-wide (350 kilometers ) moon from an icy well of bodies in the outer solar system known as the Kuiper Belt.

JWST's observations were key to this realization, said first study author Matthew Belyakov, a graduate student in planetary science at Caltech. "What JWST did for Nereid is it confirmed that it had a lot of water ice, and gave us the overall shape of the spectrum [of light]," Belyakov told Live Science in a phone call.

The telescope's observations of the moon revealed a composition that's significantly different from that of known Kuiper Belt objects, he continued. Crucially, JWST has been in space long enough to allow direct comparisons against Kuiper Belt worlds that the telescope itself has observed. "We're able to compare apples to apples," Belyakov added.

The moon-stealing planet

Previously, astronomers assumed that Nereid was "captured" by Neptune's gravity, like the planet's other known moons are suspected to have been. This is due to Nereid's orbit, which is highly elliptical — suggesting the moon was snatched from a previous, more stable orbit in the Kuiper Belt.

But that hypothesis is challenging to prove, given that Neptune has 16 known moons. Most of those moons are small, aside from Triton, which is slightly smaller than Earth's moon. The system is made up largely of small moons in irregular orbits.

"The trouble at Neptune is that we don't have any regular satellites really, whatsoever," Belyakov said.

Triton, Neptune's largest moon, represents 99% of the Neptunian moon system's mass and is on a "retrograde," or backward, orbit, Belyakov added. Triton is clearly a captured object ‪—‬ not only because of its odd orbit but also because observations have shown that its composition is more similar to Pluto's than to Neptune's, he said.

In the new study, the authors ran simulations of Triton's capture from the Kuiper Belt and how it may have affected the existing moons of Neptune. The simulations show that Triton's arrival gave the original Neptune moons a tremendous kick. "Triton gets captured and alters the original system, and creates a Nereid-like object," Belyakov explained.

Moon mysteries

To shore up this theory, Belyakov hopes to get a better look at Nereid in higher resolution. JWST is in high demand by astronomers, and Belyakov's team, which includes noted moon dynamicist and Caltech professor Konstantin Batygin, got a few minutes of telescope time using the lowest-resolution mode of JWST's Near-Infrared Spectrograph (NIRSpec). The team plans to submit an application for use of a higher-resolution mode of NIRSpec in a future call for telescope observations, he said.

These observations have implications not only for Neptune but also studies of exoplanets and gas giants, Belyakov emphasized.

"The big picture is that really we don't quite understand how moons around Uranus and Neptune form," Belyakov said. "What we're finding generally, in the study of exoplanets, is that planets of the size of Uranus and Neptune are pretty much the most common type of planet. And so if we don't understand how moons around these objects form, that's a really big problem."

The histories of Uranus and Neptune are making the study more challenging, he noted. Uranus is weirdly tilted on its side, perhaps due to a big collision with another object eons ago, which means its first generation of moons likely no longer exists.

"And at Neptune, we're also missing that first generation of moons," Belyakov said.The planet's innermost moons today were reforged from the original generation of moons that broke apart in the wake of Triton's arrival, the authors noted.

"So perhaps," he continued, "Nereid is the only original, sort of intact, remnant of satellites that originally formed around these planets. That would be a very exciting result, because it means that we have this one window to explore and understand satellites."

The interiors of Uranus and Neptune may be rockier than scientists previously thought, a new computational model suggests — challenging the idea that the planets should be called "ice giants."

The new study, published Dec. 10 in the journal Astronomy & Astrophysics, may also help to explain the planets' puzzling magnetic fields.

Uranus and Neptune are relatively large planets at the edge of the solar system; Neptune is the most distant planet, orbiting at 2.8 billion miles (4.5 billion kilometers) from the sun, on average. The extremely cold temperatures at these distances cause gases such as hydrogen, helium and water to condense into compressed ice slurries that form the planets' cores. As such, these planets have become known as ice giants.

"The ice giant classification is oversimplified as Uranus and Neptune are still poorly understood," lead study author Luca Morf, a doctoral student at the University of Zurich, said in a statement.

Far out planets

Morf and his supervisor, Ravit Helled, developed a new hybrid model in an attempt to better understand the interior of these cold planets. Models based on physics alone rely heavily on assumptions made by the modeler, while observational models can be too simplistic, Morf explained. "We combined both approaches to get interior models that are both unbiased and physically consistent," he said.

The pair started by considering how the density of each planet's core could vary with distance from the center of the planets and then adjusted the model to account for the planets' gravities. From this, they inferred the temperature and composition of the core and generated a new density profile. The team inputted the new density parameters back into the model and iterated this process until the model core fully matched current observational data.

This method generated eight total possible cores for both Uranus and Neptune, three of which had high rock-to-water ratios. This shows that the interiors of Uranus and Neptune are not limited to ice, as previously thought, the researchers said.

All of the modeled cores had convective regions where pure water exists in its ionic phase. This is where extreme temperatures and pressures cause water molecules to break apart into charged protons (H⁺) and hydroxide ions (OH^-). The team thinks such layers may be the source of the planets' multiple magnetic fields, which cause Uranus and Neptune to have more than two poles. The model also suggests that Uranus' magnetic field is generated closer to its center than Neptune's is.

"One of the main issues is that physicists still barely understand how materials behave under the exotic conditions of [high] pressure and temperature found at the heart of a planet [and] this could impact our results," Morf said. The team aims to improve their model by including other molecules, like methane and ammonia, which also may be found in the cores.

"Both Uranus and Neptune could be rock giants or ice giants depending on the model assumptions," Helled said. She noted that much of our understanding of these planets may be incomplete, as it's based largely on data collected by the Voyager 2 space probe in the 1980s.

"Current data is insufficient to distinguish the two, and we therefore need dedicated missions to Uranus and Neptune that can reveal their true nature," Helled added

The team hopes the model may act as an unbiased tool for any new data from future space missions to these planets.

Six planets — Mercury, Venus, Jupiter, Saturn, Uranus and Neptune — will appear in a dark night sky together for almost a week, beginning Sunday, Aug. 17. The fairly rare "planetary parade," which is sometimes mistakenly called a planetary alignment, will continue through Wednesday, Aug. 20.

The celestial gathering, last seen in February, will appear in the eastern sky about an hour before sunrise. Although most of these planets have been visible in the morning sky for weeks, Mercury will join the fray, bringing the planet count from five to six.

Under clear skies, you should be able to spot Venus, Jupiter and Saturn. Mercury will be closer to the horizon but still bright enough to be seen by most observers. However, Uranus (appearing between Jupiter and Saturn in the sky) and Neptune (close to Saturn in the sky) are too dim and distant to be seen with the naked eye. The only way to see these two ice giants is by using a good telescope.

Although it's relatively rare for six planets to appear in the sky simultaneously, the beauty of the view will be vastly increased by the waning crescent moon.

Related: How to photograph the moon: Tips on camera gear, settings and composition

On Aug. 17 and Aug. 18, a crescent moon will rise above Jupiter and Venus. The two brightest planets in the night sky are now slowly moving apart after an incredibly close conjunction on Aug. 12.

Mercury may be visible below Jupiter and Venus, but it will be easier to see it on Aug. 19. On that morning, and on Aug. 20, a slim crescent moon will be very close to Jupiter and Venus — a visual highlight of the "planetary parade."

By around Aug. 21, Mercury will begin to fall back into the sun's glare and will become more difficult to see.

According to the Star Walk app, there will be two six-planet parades in 2026: one after sunset in February and another before sunrise in August.

Astronomers have found that a weird space rock at the edge of the solar system is locked in a rhythmic dance with Neptune.

The object, designated 2020 VN40, is part of a family of distant solar system objects called trans-Neptunian objects (TNOs). 2020 VN40 is the first object discovered that orbits the sun once for every ten orbits Neptune makes. Considering that one Neptunian year lasts 164.8 Earth years, that means 2020 VN40 has one heck of a long year, lasting around 1,648 years or 19,776 months on Earth!

The team behind this research thinks that 2020 VN40's ponderous orbital dance with Neptune may have come about when it was temporarily snared by the gravity of the ice giant planet. Thus, this discovery could help researchers better understand the dynamics of bodies at the edge of the solar system.

"This is a big step in understanding the outer solar system," team leader Rosemary Pike from the Center for Astrophysics | Harvard & Smithsonian said in a statement. "It shows that even very distant regions influenced by Neptune can contain objects, and it gives us new clues about how the solar system evolved."

The orbital rhythm of 2020 VN40 was discovered in data from the Large inclination Distant Objects (LiDO) survey. LiDO uses the Canada-France-Hawaii Telescope with backup from the Gemini Observatory and the Walter Baade Telescope to search the outer solar system for weird objects.

In particular, LiDO specializes in hunting TNOs with orbits that take them far above and below the orbital plane of Earth around the sun. These are regions of the solar system that have thus far only been sparsely explored by astronomers.

"It has been fascinating to learn how many small bodies in the solar system exist on these very large, very tilted orbits," LiDO team member and University of Regina researcher Samantha Lawler said.

Related: James Webb telescope captures auroras on Neptune for first time ever

The highly tilted path of 2020 VN40 finds it at an average distance from the sun equivalent to 140 times the distance between Earth and our star.

However, the most interesting element of the orbit of 2020 VN40 is its resonance with the orbit of Neptune. Other bodies rhythmically aligned with Neptune make their closest approaches to the sun, their perihelion, when Neptune is at its greatest distance from our star, or its aphelion.

Defying this trend, 2020 VN40 is at perihelion when Neptune is also close to the sun. That's if one were looking at it from above the solar system, with the tilt of 2020 VN40 meaning that this TNO and Neptune are not actually close together; the TNO is actually far below the solar system.

This also separates 2020 VN40 from other resonant TNOs, which tend to stay within the plane of the solar system when they make close approaches to the sun.

"This new motion is like finding a hidden rhythm in a song we thought we knew," team member and University of California Santa Cruz scientist Ruth Murray-Clay said. "It could change how we think about the way distant objects move."

Revealing the orbital strangeness of 2020 VN40 suggests that solar system objects with highly tilted orbits can adopt novel and unexpected types of movement.

The hunt is now on for more bodies like 2020 VN40, with the newly operating Vera C. Rubin Observatory set to play a key role in this investigation.

"This is just the beginning," team member and Planetary Science Institute researcher Kathryn Volk said. "We're opening a new window into the solar system's past."

The 2020 VN40 results were published on July 7 in The Planetary Science Journal.

This article was originally published on Space.com.

When you think of a planet with rings, majestic Saturn almost definitely comes to mind. But it's not the only planet in the solar system with these breathtaking bands. So which planets in our solar system have rings?

All four giant planets — Jupiter, Saturn, Uranus and Neptune — sport these spectacular structures. Plus, many other objects in the solar system, including the dwarf planet Haumea and asteroid Chariklo, have rings. Whether or not we can see these rings easily from Earth depends on what they're made of.

Unlike a diamond ring, planets' rings don't last forever — not even the most iconic ones in the solar system. Scientists think Saturn's rings will vanish as the debris that makes up the rings falls into Saturn's atmosphere, but that won't happen for a long time.

"We still have hundreds of millions of years to enjoy them," Saunders said. "But it makes me think about how lucky we are to live at a time when Saturn has beautiful, icy, visible rings."

Astronomers searching for a ninth planet in our solar system say they've found a "good" candidate far beyond Neptune, according to a new preprint study.

This could be humanity's first glimpse at the long-theorized Planet Nine, which — if it exists — is a giant, undiscovered world distantly orbiting our sun. However, the ninth planet proposal is contentious, and the new findings are unlikely to change that.

Researchers discovered this latest planetary candidate while studying old satellite data. At this stage, the candidate is simply a curious dot across a few infrared images. But the dot seemed to be moving in a way that was consistent with a large, distant planet.

"I felt very excited," study lead-author Terry Phan, an astronomy doctoral student at the National Tsing Hua University in Taiwan, told Science, recalling the discovery. "It's motivated us a lot."

Phan and his colleagues posted their findings to the preprint server arXiv on April 24, which have been accepted for publication in the journal Publications of the Astronomical Society of Australia. However, the preprint has been met with some skepticism.

Mike Brown, an astronomer at Caltech who first proposed the Planet Nine hypothesis with a colleague in 2016, isn't convinced that the infrared dots correspond to the elusive planet. Brown wasn't involved in the study, but calculated the orbit of the infrared signal and found that the object would be tilted about 120 degrees from the Solar System's plane, Science reported. That tilt is much greater than Planet Nine's predicted tilt of around 15 to 20 degrees, and also means this object would be orbiting in a different direction from the known planets, which all sit roughly on the same plane.

This mismatch "doesn't mean it's not there, but it means it's not Planet Nine," Brown told Science. "I don't think this planet would have any of the effects on the Solar System that we think we're seeing."

Related: How long would it take to reach Planet 9, if we ever find it?

The predicted position of Planet Nine is meant to explain the irregular orbits of some objects in the Kuiper Belt at the far reaches of our solar system. However, some researchers are unconvinced that these orbits are caused by an undiscovered planet, and the scientific community as a whole is still waiting for any direct observational evidence of Planet Nine's existence.

If Planet Nine does exist, then researchers have predicted that it's much larger than Earth and orbits in an unusual pattern billions of miles beyond Neptune — the eighth and, as things stand, final planet in our solar system. Planet Nine's supposed orbit is so far away from the sun that it would be difficult for Earthling scientists to detect, hence why they're having a hard time proving or disproving its existence.

The team behind the new study searched for Planet Nine candidates in the data archives of two decommissioned satellites: the 1983 Infrared Astronomical Satellite (IRAS) and the 2006-2011 AKARI satellite, Live Science's sister site Space.com reported. They were looking for distant objects that moved slowly between one set of data and the next, like the proposed Planet Nine would be doing if it were orbiting our sun.

After ruling out the known objects in the data, the researchers zeroed in on a shortlist of candidates. They then pored over images of these potential objects and eventually came away with what they described in the study as "one good candidate." The candidate is a dot with the same colors and brightness across the two sets of images, suggesting it's one object captured by both satellites. Follow-up observations are needed to determine the object's full orbit, according to the study.

Brown told Science that if the infrared signal is a planet, then based on his calculations, it couldn't exist alongside the original hypothesized Planet Nine without the two making each other's orbits unstable. Thus, the new candidate for Planet Nine could be a different planet with the potential to disprove the Planet Nine hypothesis.

The existence of Planet Nine — or any other undiscovered ninth planet in our solar system — will likely remain a contentious subject for now. However, 2025 could prove to be the beginning of the end for the search.

The Vera C. Rubin Observatory, currently under construction in Chile, will open later this year and has the potential to settle the Planet Nine debate. This state-of-the-art observatory will feature the world's largest digital camera and look deeper into space than its predecessors. Researchers are hoping it will be able to spot Planet Nine within a year or two, if it's out there at all.

New James Webb Space Telescope (JWST) images have captured auroras on Neptune for the first time.

The telescope spotted infrared auroras that create exotic molecules known as trihydrogen cations, according to a study published March 26 in Nature. Scientists identified auroras on Jupiter, Saturn, and Uranus more than 30 years ago, but Neptune's auroras staunchly evaded detection until now.

Auroras form when energetic, charged particles from the sun get caught up in a planet's magnetic field. The field funnels the particles toward the planet's magnetic poles, where they collide with — and ionize — atmospheric molecules along the way, causing them to glow.

Unlike auroras on Earth, which occur at extreme northern and southern latitudes near our planet's North and South Pole, Neptune's auroras appear near the planet's mid-latitudes. That's because Neptune's magnetic field is tilted 47 degrees off its rotational axis, so the planet's magnetic poles lie between the geographic poles and the equator — around where South America would be located on Earth.

And unlike the Northern Lights, Neptune's auroras aren't visible to the naked eye.

"Turns out, actually imaging the auroral activity on Neptune was only possible with Webb's near-infrared sensitivity," Henrik Melin, a planetary scientist at Northumbria University in the U.K., said in a statement. "It was so stunning to not just see the auroras, but the detail and clarity of the signature really shocked me."

Finishing Voyager's work

In June 2023, researchers used JWST's Near-Infrared Spectrograph to look for the trihydrogen cation (H₃⁺), a hallmark of auroral activity in the hydrogen-rich atmospheres of the solar system's gas giants. NASA's Voyager 2 probe flew by Neptune in 1989, but it didn't have the right equipment to detect the cation. Since then, scientists at ground-based facilities, such as Hawaii's Keck telescope and NASA Infrared Telescope Facility, have looked for this molecule in Neptune's atmosphere without success, despite predictions that it should be present.

Related: 'Hidden' rings of Uranus revealed in dazzling new James Webb telescope images

This time, JWST detected H₃⁺, but researchers also noted unexpected changes in Neptune's atmosphere. "I was astonished — Neptune's upper atmosphere has cooled by several hundreds of degrees [since the Voyager flyby]," Melin said in the statement. "In fact, the temperature in 2023 was just over half of that in 1989."

These cold temperatures could be why scientists haven't detected H₃⁺ on Neptune until now. The auroras appear much fainter at cold temperatures, and light reflecting off Neptune's clouds may have drowned them out, the researchers said.

"As we look ahead and dream of future missions to Uranus and Neptune, we now know how important it will be to have instruments tuned to the wavelengths of infrared light to continue to study the auroras," study coauthor Leigh Fletcher, a planetary scientist at Leicester University in the U.K., said in the statement. "This observatory has finally opened the window onto this last, previously hidden ionosphere of the giant planets."

A stunning photo has captured all seven of our neighboring planets in Earth's sky at the same time, possibly for the first time ever.

The composite image, captured by astrophotographer Josh Dury, shows Mars, Jupiter, Uranus, Saturn, Venus, Neptune and Mercury in alignment thanks to a rare "planetary parade" taking place this weekend for the first time since 1982. (Here's how you can see it for yourself tonight).

While spacecraft, such as NASA's Voyager 1, have snapped all the planets in the sky from space, terrestrial cameras have only recently become advanced enough to capture them from the ground — meaning Dury's photo is likely the very first of its kind.

"Seven (arguably, 8) is a feat that to my prior knowledge has not been achieved before," Dury told Live Science in an email — suggesting that if we include Earth itself, visible in the foreground, the image's planet total comes to eight. "This image could hold a record for being the first of its kind to photograph all the planets of the solar system, blended into a stitched panoramic image."

Dury captured the image just after sundown on Feb. 22 from The Mendip Hills — a range of limestone hills in Somerset in the U.K.

Related: Have all 8 planets ever aligned?

To achieve this photographic feat, Dury created a composite shot made up of several panes, with each pane captured in multiple exposures.

To locate Saturn, Neptune and Mercury, which were dimmer and closer to the western horizon, Dury used astronomy software to generate models of the night sky and match planetary locations to nearby star fields. He then used a high dynamic range (HDR) camera setting to capture the planets' faint light.

"I noted that when I took the image that it would not, of course, be possible to photograph the lowest planets at the moment of sunset — glare from the sun rendering this task impossible," Dury said. "Therefore, this image is a record of the first possible glimpse of the planets as light from the sun diminished." The night-sky models enabled him to later identify the planets in the image.

Planetary conjunctions occur when two or more planets appear to be close together in the sky. Of course, this is only from our perspective of the cosmos on Earth — in reality the planets remain extremely far apart.

These conjunctions aren't rare, but they get rarer with each planet added to the chain. For example, the three innermost planets — Mercury, Venus and Earth — align within 3.6 degrees in the sky every 39.6 years. For all of the solar system's eight planets to align as closely, it would take 396 billion years, something that has never happened and won't happen before the sun becomes a red giant, consuming Mercury, Venus and likely Earth in the process.

However, it is a little less unusual for all seven planets to appear spread out on the same side of the sun, as they do in Dury's image and in the night sky right now. Another seven-planet parade is expected to be visible from Earth in 2040.

If you'd like to see a planetary alignment for yourself, tonight (Feb. 28) is one of the best times to look. Time and Date and Stellarium are two great online tools for finding viewing times based on your location.

Seven planets in the solar system — Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune — will line up in the night sky Friday (Feb. 28) in an incredibly rare "planetary parade."

Although most of these planets have been visible in the night sky since January, Mercury will be joining the procession for just a few days, before Saturn gets lost in the sunset's glare in early March.

Five of these worlds will be easily visible to the unaided eye, but you will need a good telescope to see the full show, according to NASA.

That's because at least two of the planets — Uranus and Neptune — will be too dim to see with the naked eye and will likely be masked by the glare of the setting sun at twilight, NASA said. Saturn will also be trickier to see in some locations due to its position close to the horizon.

If you have a good telescope to catch the full display, the best time to view all seven planets in the Northern Hemisphere will be after sunset on Friday (Feb. 28) at around 8:30 p.m. local time, according to SkyatNightMagazine.

Related: Have all 8 planets ever aligned?

Planetary conjunctions occur when two or more planets appear to be close together in the sky. Of course, this is only from our perspective on Earth; in reality, the planets remain extremely far apart.

Conjunctions happen because the planets of the solar system orbit the sun along roughly the same flat plane as Earth, and they occasionally align when their different orbital distances and speeds bring them into a cluster on Earth's nightside.

These conjunctions aren't rare, but they do get rarer with each planet added to the chain. The three innermost planets — Mercury, Venus and Earth — align within 3.6 degrees in the sky every 39.6 years. For all of the solar system's eight planets to align that closely, it would take 396 billion years — something that has never happened and won't happen before the sun becomes a red giant, consuming Mercury, Venus and likely Earth in the process.

We recommend Time and Date and Stellarium as two great online tools for finding viewing dates and times based on where you are in the world. On mobile phones, Sky Tonight is a free app that will do the same job.

A striking new "planetary parade" photo combines images of six solar system worlds alongside the moon, providing a rare opportunity to compare the sizes of these celestial objects as they currently appear from Earth.

French astrophotographer Gwenaël Blanck created the stunning image by combining individual shots of each of the objects captured Feb. 2 from Paris, where he also took an exceptional photo of Venus and the moon aligning above the Eiffel Tower a day earlier.

The individual images were captured between 6:30 p.m. and 7:50 p.m. local time, using a digital camera attached to a telescope. Blanck then made a composite image of the six worlds in a straight line for the final photo. The objects are arranged from closest to Earth (left) to farthest from our planet (right): the moon, Venus, Mars, Jupiter, Saturn, Uranus and Neptune.

"I had to start quite early, shortly after sunset, to image Venus and Saturn before they were too low on the horizon," Blanck told Live Science in an email. "Neptune was also not far away [from the horizon]," he added. "It was probably the most difficult to capture."

"The Moon, Uranus, Jupiter and Mars were easier to capture, as they were higher in the sky," Blanck said. "The only missing planet was Mercury, which will become visible towards the end of the month and early March."

Related: Have all 8 planets ever aligned?

In reality, the objects in the image were scattered across the night sky. However, Blanck used the same magnification settings for each image, meaning the objects' sizes are perfectly scaled. That is why the moon looks so massive compared with Uranus and Neptune and why Venus and Jupiter appear to be around the same size, despite the latter being more than 10 times wider than the former.

"This gives a pretty good idea of the apparent size of each planet," Blanck said.

Planetary parade

We are currently in the midst of one of the most impressive planetary alignment events in recent years. Under the right circumstances, five planets — Mercury, Venus, Mars, Jupiter and Saturn — will be visible to the naked eye over the next few weeks. Uranus and Neptune are also present in the night sky, but you'll need a good telescope to see them alongside their brighter neighbors.

The event has already delivered some special moments, including an earlier alignment of six of the seven planets in late January and an occultation of Mars by the moon on Feb. 9. However, the parade will not peak until late February and early March, when all seven planets will align in a near-straight line along the horizon, according to Live Science's sister site Space.com.

Venus will be the brightest planet in the night sky during this period; it will be closest to the moon in the sky, making it easy to spot on most clear nights. The "love planet" will reach its peak brightness in time for Valentine's Day (Feb. 14).

If you want to see the best of the planetary parade for yourself, we recommend using a decent telescope or a pair of stargazing binoculars.

The next time we will see a similar alignment of the planets will be in October 2028.

New James Webb Space Telescope (JWST) findings are giving scientists a fresh look at an "oddball" space rock that has features similar to both comets and asteroids.

Astronomers observing the hybrid, known as (2060) Chiron, detected frozen carbon dioxide and carbon monoxide in its icy nucleus, as well as carbon dioxide and methane in the surrounding gas cloud. The findings could help scientists better understand comets and centaurs — so named because they have properties of both asteroids and comets — and could offer a peek at the conditions in the early solar system.

Discovered in 1977, Chiron orbits the sun about once every 50 years, traveling in an oblong loop in the region between Jupiter and Neptune. In the new study, published Dec. 18 in the journal Astronomy and Astrophysics, researchers described their observation of the centaur on July 12, 2023 at a range of more than 18 times the distance from Earth to the sun.

Related: Comets played a 'major' role in making life on Earth possible, new study hints

The team found carbon dioxide and methane gases in Chiron's coma, the cloud of gas and dust around the nucleus. Though previous studies had detected carbon monoxide gas in the coma as well, the new JWST observations found carbon monoxide only in its frozen form on Chiron's surface. The finding suggests a complex scenario of gas emissions from different reservoirs on Chiron, the researchers wrote in the study. In general, carbon monoxide is more volatile, and therefore more likely than CO2 to sublimate, or transform directly from a solid on the surface to a gas released in the coma.

Detecting gas in our solar system

"These results are like nothing we've seen before," study co-author Charles Schambeau, a planetary scientist at the University of Central Florida (UCF), said in a statement. "Detecting gas comae around objects as far away from the sun as Chiron is very challenging, but JWST has made it accessible. These detections enhance our understanding of Chiron's interior composition and how that material produces the unique behaviors as we observe Chiron."

Astronomers also detected water ice and lightweight carbon-containing molecules like ethane and propane for the first time on a centaur. Chiron could have picked up simpler molecules like carbon dioxide and water left by the nebula that formed our solar system, study co-author Noemi Pinilla-Alonso, a planetary scientist at UCF and the University of Oviedo in Spain, said in the statement. Objects like Chiron haven’t changed much since the solar system first formed, she said, so observing how they interact on Chiron could help scientists better understand the early solar system. Molecules like ethane and propane, meanwhile, likely formed when light hit the surface and reacted with the methane and water ice there.

However, fully understanding the compositions of the nucleus and coma, and how they change during Chiron's orbit, will require additional data.

"We're going to follow up with Chiron," Pinilla-Alonso said in the statement. "It will come closer to us, and if we can study it at nearer distances and get better reads on the quantities and nature of the ices, silicates, and organics, we will be able to better understand how seasonal insolation variations and different illumination patterns can affect its behavior and its ice reservoir."

Scientists have uncovered the secret ingredient fueling supercharged storms on Uranus and Neptune: methane.

Uranus and Neptune are the outermost planets of the solar system and are known as ice giants because they are rich in water. Scientists understand very little about these distant realms. But after the Voyager 2 spacecraft flew by them in the 1980s, scientists realized that these worlds occasionally host massive, short-lived storms. The violent-but-fleeting storms pop up every few years and are so big you can see them (with a telescope) from Earth.

Researchers have long wondered why the storms on these planets are so unpredictable. Now, a team of astronomers has proposed that methane may hold the key to controlling these storms.

To power a storm, heat must rise from a planet's warm interior to its surface. There, the heated gas begins to cool, which can cause turbulence and trigger storm formation. But the interiors of these planets are always warm, and the outer surfaces are always cool, so why don't storms occur all the time?

In a paper published to the preprint database arXiv on Sept. 3, the team pointed out that methane is the third-most abundant molecule, after hydrogen and helium, in the deep atmospheres of both worlds. Normally, methane doesn't do much except float around in the atmosphere, but the researchers used modeling to show that in certain circumstances, this simple hydrocarbon can dramatically alter heat transfer within the planet.

Methane usually exists as a gas, but in the upper regions of these ice world atmospheres, methane may condense, forming droplets that fall to lower altitudes, the study authors proposed. There they reheat and rise again, completing a cycle similar to the water cycle on Earth. Once the atmosphere becomes too saturated with methane, a stable layer forms. Like a wet blanket, the stable layer keeps heat from reaching the surface, which in turn suppresses storm formation.

These layers are most commonly found throughout all latitudes of Neptune, and around the equator and mid-latitudes of Uranus. But the poles of Uranus don't have enough methane to create a stable saturated layer. As a result,heat can easily rise to the surface and drive larger storms, the study found.

On the other hand, Neptune has more methane overall, and the researchers found that occasionally that methane can rise from the stable layer and disperse through the atmosphere, enabling heat to flow and storms to form, before everything settles down again.

Further work will be needed to understand how all the factors in these ice-giant atmospheres interact

That knowledge could then be used to better understand planets beyond the solar system, the study authors wrote.

What it is: One of the final photographs of Neptune taken by NASA's Voyager 2 probe

Where it is: 2.8 billion miles (4.5 billion kilometers) from the sun

When it was taken: Aug. 25, 1989

When it was shared: Aug. 19, 2024

Why it's so special: Only one spacecraft has ever visited the eighth and most distant planet from the sun.

On Aug. 25, 1989, NASA's Voyager 2 spacecraft took the first-ever close-up images of Neptune. This one — among the last full-disk photos taken before the probe ended its "Grand Tour" of the planets — became one of the most iconic. It revealed Neptune as a deep azure blue, which colored the public's perception of the planet for decades. (That is, until a new treatment of Voyager 2's images earlier this year revealed Neptune's true color to be a much lighter blue green.)

Voyager 2's original images were taken in false color using filters — a standard technique used by planetary astronomers. In this case, blue and green filters were used alongside one that passes light at a wavelength absorbed by methane gas. According to scientists, hydrogen and helium dominate Neptune's atmosphere, but methane gives it its blue appearance by absorbing red light. The filters make methane look dark blue in this image, but they also reveal a semitransparent haze layer across the planet. The bright-red edge around Neptune is caused by the haze scattering sunlight at higher altitudes, above most of the methane.

Related: Uranus and Neptune aren't made of what we thought, new study hints

Voyager 2 took this shot almost precisely 12 years after it launched on a Titan-Centaur rocket from Cape Canaveral, Florida. Having visited Jupiter in 1979, Saturn in 1981 and Uranus in 1985, Voyager's closest approach to Neptune came on Aug. 25, 1989. During the flyby, Voyager also visited two of Neptune's moons, Triton and Nereid, and discovered six new moons and four rings.

Because Neptune is about 30 times farther from the sun than Earth is, it gets only a faction of a percent of Earth's sunlight, meaning Voyager 2 had to take long-exposure images. So engineers fired the fast-moving spacecraft's thrusters to have it rotate so the camera could remain focused.

Voyager 2's images from Neptune were its last, sent back as radio signals with 13-watt transmitters — about enough power to run a refrigerator light bulb, according to NASA — and took four hours to travel across the solar system to NASA's Deep Space Network of radio antennae across the world.

Neptune was Voyager 2's last stop before it traveled to the solar system's edge. The probe entered interstellar space on Nov. 5, 2018. Voyager 2 remains NASA's longest-running mission, even after encountering some communication problems last summer.

For more groovy space photos, check out our space photo of the week archives. New stories post every Sunday.

Some experts believe that we could be just a few years away from discovering the elusive "Planet Nine" — or ruling out the existence of the hypothetical world for good. 

But if we do find it, how long would it take for us to send a spacecraft to the far-flung world? And could humans ever make the trip?

Planet Nine is the name given to a proposed planet supposedly lurking near the edge of the solar system. If it exists, Planet Nine is likely a dark, gas or ice giant planet somewhere between five and 10 times the mass of Earth that circles the sun on a highly elliptical, or stretched, orbit — out of sync with the rest of the planets.

Researchers suspect Planet Nine is out there because around a dozen objects beyond the orbit of Neptune, move as if a large object is tugging on them. However, finding this missing world has proved to be extremely tricky.

But some astronomers believe Planet Nine could be discovered within the next few years once the state-of-the-art Vera C. Rubin Observatory starts to survey the night sky in late 2025. 

Related: Elusive Planet Nine could be surrounded by hot moons, and that's how we'd find it

If Planet Nine is ever detected, space agencies like NASA will want to send a probe to visit the distant world. But first, they will have to plan and get approval for such a mission. 

"This will take at least a decade or more," Andreas Hein, a space systems engineer at the University of Luxembourg, told Live Science in an email. This is mostly because missions have to go through a lengthy and rigorous government selection process, he added.

But this process could be sped up depending on how odd the world appears in initial readings, Manasvi Lingam, a theoretical astrobiologist at the Florida Institute of Technology, told Live Science in an email. "If Planet 9 is anomalous in some respect, there could be more interest in expediting such a mission."

It is also possible that a private space exploration company, such as SpaceX, could launch missions sooner — potentially as soon as five years after discovery — because they are not hindered by as much bureaucracy, Hein said.

Reaching Planet Nine

Once a probe is sent to Planet Nine, the next question is how long will it take to arrive?

In 2022, Hein, Lingam and part-time astronomer Adam Hibberd attempted to answer this question in a theoretical paper that was posted to the pre-print database arXiv. In this paper, which has not been peer-reviewed, the researchers estimated that it would likely take between 45 and 75 years for a spacecraft akin to NASA's Voyager probes to reach Planet Nine.

These calculations were based on the assumption that Planet Nine is around 400 astronomical units from the sun on average, or 400 times farther away from the sun than Earth. That's also around 13 times further away from the sun than Neptune, the farthest known planet in the solar system. 

But subsequent studies suggest that Planet Nine's true average distance from the sun is actually closer to 500 astronomical units. And the most recent survey, which narrowed down the elusive world's potential hiding place, also hints that the planet could currently be more than 550 astronomical units away, near its farthest point from the sun.

However, these developments don't dramatically alter the timeline laid out in the 2022 paper, Lingam said. The team's estimates were "conservative," meaning that the upper end of their uncertainty range "still seems tenable," he added.

Pushing boundaries

Seventy-five years may seem like a long time for a one-way trip. But this is quite fast compared to the journeys of existing probes; for example, Voyager 1 — the most distant spacecraft from Earth — has been traveling through space for 46 years and is only around 163 astronomical units from Earth, according to NASA. As a result, a Planet Nine probe would have to travel around three times faster than Voyager 1 to reach Planet Nine in the researcher's timeframe. 

This may seem unlikely but it is possible, Lingam said. 

Probes traveling toward the outer solar system must be gravitationally slingshotted around the sun, planets and their moons to propel them across the vast distances involved. Voyager 1's trajectory was carefully planned to allow it to fly closely past Jupiter, Saturn, Uranus and Neptune, as well as some of their respective moons. To do so, Voyager 1 had to also be slingshotted around objects to slow it down and redirect it to where it needed to go. However, a Planet Nine probe could go as directly as possible straight to the mysterious planet, allowing it to pick up more speed and travel much further in the same amount of time.

Related: Elusive Planet Nine could be an alternative form of gravity masquerading as a planet, study claims

Mike Brown, an astronomer at Caltech who co-proposed the Planet Nine hypothesis in 2016, originally estimated that a probe could potentially get to Planet Nine in as few as 20 years using a similar method. However, it is "difficult" to see how a probe could get to Planet Nine this fast using current technology, Lingam said. 

But it might be possible to reach Planet Nine quicker if we could crack more advanced propulsion technologies, such as light sails — giant sails that catch sunlight or lasers to accelerate spacecraft, Hein and Lingam said. 

In the 2022 study, the researchers suggested that a light sail could take as little as seven years to reach Planet Nine. However, it could take at least 20 years for light sails to become a reality, the team estimated. 

As a result, if we found Planet Nine tomorrow, it would be better to send a current probe than to wait for alternative technologies to become available, Lingam said. "Laser sails can be launched later, if and when they become practical and cost-effective."

As propulsion systems advance further, it may also be possible to send people to Planet Nine. But probably not anytime soon.

"I am confident that in the far future, humans will be able to visit Planet Nine," potentially even as they make their way to other stars, Hein said. 

A rare and stunning photo recently captured a "parade of planets," in which six planets in our solar system appeared together in the predawn sky.

The image shows Mercury, Mars, Jupiter, Saturn, Uranus and Neptune in alignment. Mars and Saturn are clearly visible near a crescent moon, while the positions of the remaining planets, which were too distant to be seen with the naked eye, were revealed by two composite long exposures. 

Astrophotographer Josh Dury captured the planetary parade on June 1 in the early hours of the morning from The Mendip Hills — a range of limestone hills in the county of Somerset in the U.K. on June 1. 

The annotated image shows Mars and Saturn clearly visible near a crescent moon, while the positions of the remaining planets (too distant to be seen with the naked eye but faintly visible in the image) were revealed by two composite long exposures.

"I thought no better than to climb Crooks Peak at the unearthly hour of 2am," Dury told Live Science via email. "As time passed, it was a really special experience. Being able to see one planet after another rising and being present in my images was fantastic and really encapsulated a sense of perspective of our place within the solar system, let alone the universe."

Related: Have all 8 planets ever aligned?

Planetary conjunctions occur when two or more planets appear to be close together in the sky. Of course, this is only from our perspective of the cosmos on Earth — in reality the planets remain extremely far apart.

These conjunctions aren't rare, but they do get rarer with each planet added to the chain. The three innermost planets  — Mercury, Venus and Earth — align within 3.6 degrees in the sky every 39.6 years. For all of the solar system's eight planets to align as closely, it would take 396 billion years — something that has never happened and won't happen before the sun becomes a red giant, consuming Mercury, Venus and likely Earth in the process, Live Science previously reported. 

If you'd like to see a planetary alignment for yourself, Time and Date and Stellarium are two great online tools for finding viewing dates and times based on where you are in the world.

I was once sitting with my father while Googling how far away various things in the solar system are from Earth. He was looking for exact numbers, and very obviously grew more invested with each new figure I shouted out. I was thrilled. The moon? On average, 238,855 miles (384,400 kilometers) away. The James Webb Space Telescope? Bump that up to about a million miles (1,609,344 km) away. The sun? 93 million miles (149,668,992 km) away. Neptune? 2.8 billion miles (4.5 billion km) away. "Well, wait until you hear about Voyager 1," I eventually said, assuming he was aware of what was coming. He was not.

"NASA's Voyager 1 interstellar spacecraft actually isn't even in the solar system anymore," I announced. "Nope, it's more than 15 billion miles (24 billion km) away from us — and it's getting even farther as we speak." I can't quite remember his response, but I do indeed recall an expression of sheer disbelief. There were immediate inquiries about how that's even physically possible. There were bewildered laughs, different ways of saying "wow," and mostly, there was a contagious sense of awe. And just like that, a new Voyager 1 fan was born.

It is easy to see why Voyager 1 is among the most beloved robotic space explorers we have — and it is thus easy to understand why so many people felt a pang to their hearts several months ago, when Voyager 1 stopped talking to us.

Related: After months of sending gibberish to NASA, Voyager 1 is finally making sense again

For reasons unknown at the time, this spacecraft began sending back gibberish in place of the neatly organized and data-rich 0's and 1's it had been providing since its launch in 1977. It was this classic computer language which allowed Voyager 1 to converse with its creators while earning the title of "farthest human made object." It's how the spacecraft relayed vital insight that led to the discovery of new Jovian moons and, thanks to this sort of binary podcast, scientists incredibly identified a new ring of Saturn and created the solar system's first and only "family portrait." This code, in essence, is crucial to Voyager 1's very being.

Plus, to make matters worse, the issue behind the glitch turned out to be associated with the craft's Flight Data System, which is literally the system that transmits information about Voyager 1's health so scientists can correct any issues that arise. Issues like this one. Furthermore, because of the spacecraft's immense distance from its operators on Earth, it takes about 22.5 hours for a transmission to reach the spacecraft, and then 22.5 hours to receive a transmission back. Alas, things weren't looking good for a while — for about five months, to be precise.

But then, on April 20, Voyager 1 finally phoned home with legible 0's and legible 1's.

"The team had gathered early on a weekend morning to see whether telemetry would return," Bob Rasmussen, a member of the Voyager flight team, told Space.com. "It was nice to have everyone assembled in one place like this to share in the moment of learning that our efforts had been successful. Our cheer was both for the intrepid spacecraft and for the comradery that enabled its recovery."

And then, on May 22, Voyager scientists released the welcome announcement that the spacecraft has successfully resumed returning science data from two of its four instruments, the plasma wave subsystem and magnetometer instrument. They're now working on getting the other two, the cosmic ray subsystem and low energy charged particle instrument, back online as well. Though there technically are six other instruments onboard Voyager, those had been out of commission for some time.

The comeback

Rasmussen was actually a member of the Voyager team in the 1970s, having worked on the project as a computer engineer before leaving for other missions including Cassini, which launched the spacecraft that taught us almost everything we currently know about Saturn. In 2022, however, he returned to Voyager because of a separate dilemma with the mission — and has remained on the team ever since.

"There are many of the original people who were there when Voyager launched, or even before, who were part of both the flight team and the science team," Linda Spilker, a planetary scientist at NASA's Jet Propulsion Laboratory, who also worked on the Voyager mission, told Space.com in the This Week from Space podcast on the TWiT network. "It's a real tribute to Voyager — the longevity not only of the spacecraft, but of the people on the team."

To get Voyager 1 back online, in rather cinematic fashion, the team devised a complex workaround that prompted the FDS to send a copy of its memory back to Earth. Within that memory readout, operators managed to discover the crux of the problem — a corrupted code spanning a single chip — which was then remedied through another (honestly, super interesting) process to modify the code. On the day Voyager 1 finally spoke again, "you could have heard a pin drop in the room," Spilker said. "It was very silent. Everybody's looking at the screen, waiting and watching." 

Of course, Spilker also brought in some peanuts for the team to munch on — but not just any peanuts. Lucky peanuts. 

It's a longstanding tradition at JPL to have a peanut feast before major mission events like launches, milestones and, well, the possible resurrection of Voyager 1. It began in the 1960s, when the agency was trying to launch the Ranger 7 mission that was meant to take pictures of and collect data about the moon's surface. Rangers 1 through 6 had all failed, so Ranger 7 was a big deal. As such, the mission's trajectory engineer, Dick Wallace, brought lots of peanuts for the team to nibble on and relax. Sure enough, Ranger 7 was a success and, as Wallace once said, "the rest is history." 

Voyager 1 needed some of those positive snacky vibes. 

"It'd been five months since we'd had any information," Spilker explained. So, in this room of silence besides peanut-eating-noises, Voyager 1 operators sat at their respective system screens, waiting. 

"All of a sudden it started to populate — the data," Spilker said. That's when the programmers who had been staring at those screens in anticipation leapt out of their seats and began to cheer: "They were the happiest people in the room, I think, and there was just a sense of joy that we had Voyager 1 back."

Eventually, Rasmussen says the team was able to conclude that the failure probably occurred due to a combination of aging and radiation damage by which energetic particles in space bombarded the craft. This is also why he believes it wouldn't be terribly surprising to see a similar failure occur in the future, seeing as Voyager 1 is still roaming beyond the distant boundaries of our stellar neighborhood just like its spacecraft twin, Voyager 2.

To be sure, the spacecraft isn't fully fixed yet — but it's lovely to know things are finally looking up, especially with the recent news that some of its science instruments are back on track. And, at the very least, Rasmussen assures that nothing the team has learned so far has been alarming. "We're confident that we understand the problem well," he said, "and we remain optimistic about getting everything back to normal — but we also expect this won't be the last."

In fact, as Rasmussen explains, Voyager 1 operators first became optimistic about the situation just after the root cause of the glitch had been determined with certainty. He also emphasizes that the team's spirits were never down. "We knew from indirect evidence that we had a spacecraft that was mostly healthy," he said. "Saying goodbye was not on our minds."

"Rather," he continued, "we wanted to push toward a solution as quickly as possible so other matters on board that had been neglected for months could be addressed. We're now calmly moving toward that goal."

The future of Voyager's voyage

It can't be ignored that, over the last few months, there has been an air of anxiety and fear across the public sphere that Voyager 1 was slowly moving toward sending us its final 0 and final 1. Headlines all over the internet, one written by myself included, have carried clear, negative weight. I think it's because even if Voyager 2 could technically carry the interstellar torch post-Voyager 1, the prospect of losing Voyager 1 felt like the prospect of losing a piece of history. 

"We've crossed this boundary called the heliopause," Spilker explained of the Voyagers. "Voyager 1 crossed this boundary in 2012; Voyager 2 crossed it in 2018 — and, since that time, were the first spacecraft ever to make direct measurements of the interstellar medium." That medium basically refers to material that fills the space between stars. In this case, that's the space between other stars and our sun, which, though we don't always think of it as one, is simply another star in the universe. A drop in the cosmic ocean.

"JPL started building the two Voyager spacecraft in 1972," Spilker explained. "For context, that was only three years after we had the first human walk on the moon — and the reason we started that early is that we had this rare alignment of the planets that happens once every 176 years." It was this alignment that could promise the spacecraft checkpoints across the solar system, including at Jupiter, Saturn, Uranus and Neptune. Those checkpoints were important for the Voyagers in particular. Alongside planetary visits come gravity assists, and gravity assists can help fling stuff within the solar system — and, now we know, beyond.

As the first humanmade object to leave the solar system, as a relic of America's early space program, and as a testament to how robust even decades-old technology can be, Voyager 1 has carved out the kind of legacy usually reserved for remarkable things lost to time.

"Our scientists are eager to see what they’ve been missing," Rasmussen remarked. "Everyone on the team is self-motivated by their commitment to this unique and important project. That's where the real pressure comes from." 

Still, in terms of energy, the team's approach has been clinical and determined. 

"No one was ever especially excited or depressed," he said. "We're confident that we can get back to business as usual soon, but we also know that we're dealing with an aging spacecraft that is bound to have trouble again in the future. That's just a fact of life on this mission, so not worth getting worked up about."

Nonetheless, I imagine it's always a delight for Voyager 1's engineers to remember this robotic explorer occupies curious minds around the globe. (Including my dad's mind now, thanks to me and Google.)

As Rasmussen puts it: "It's wonderful to know how much the world appreciates this mission."

Originally posted on Space.com.

Six of the planets in our solar system — Mercury, Mars, Jupiter, Saturn, Uranus and Neptune — are about to align on June 3 in what some media outlets are dubbing a "parade of planets." The sight is predicted to be best visible an hour before sunrise on June 3 and June 4.

But, despite a flurry of breathless coverage promising otherwise, you won't be able to see all six planets as they rise before dawn. What you can see depends on a variety of factors, including how early you wake up, how much light pollution you have to contend with, and whether you've got a pair of stargazing binoculars or a good small telescope to aid you. 

With that in mind, up to four of the planets on display (Mercury, Jupiter, Uranus and Neptune) may either be too dim to see with the naked eye or masked by the glare of the rising sun, skywatching journalist Jamie Carter wrote for Forbes. 

The remaining planets — Mars and Saturn — will be visible, though they will likely  appear dim in the predawn hours, when the alignment is predicted to occur, Carter added. (Mars and Saturn have actually been visible just before dawn all month long, rising steadily higher each morning in May, Earthsky.com notes.)

Related: Have all 8 planets ever aligned?

However, in a recent video from the National Science Foundation, astrophysicist Joe Pesce paints a more optimistic picture of the alignment.

"It's likely that we'll be able to see Mercury, certainly Jupiter, Mars and Saturn," Pesce said. "Uranus and Neptune are also involved, but you'd need binoculars or a telescope to be able to see those two planets."

Pesce added that the alignment will be visible for a few days before and after June 3, also. And if you don't have a great view of this particular planetary parade, "there's another event in late August, and several predicted for 2025," Pesce said.

All of this means that it may be risky to get up at the crack of dawn to see the upcoming parade of planets, with as many as four of the six planets involved possibly obscured in some way. Take your local weather conditions and light pollution into account before making your plans.

For those who do sacrifice their sleep to catch a glimpse of the alignment, you won’t be entirely let down. That's because on the nights in question, a beautiful crescent moon will be visible near Mars and Saturn, Carter notes.

If you're curious about this alignment, or other upcoming ones, Time and Date and Stellarium are two great online tools for finding viewing dates and times based on where you are in the world, and will even show you the locations of the four hidden planets on June 3. On mobile phones, the Sky Tonight is a free app that will do the same job.

Editor's note: This article was updated on May 31 to include new predictions from the National Science Foundation.

Astronomers have long believed that the ice giants Uranus and Neptune are rich in frozen water. However, a new study suggests they may also have tons of methane ice.

The findings could help solve a puzzle about how these icy worlds formed.

Much about Uranus and Neptune remains unknown. These ice giant worlds have had just a single spacecraft visitor, Voyager 2, which flew past them in the 1980s. As a result, scientists have only a hazy idea of the ice giants' compositions — for example, that they contain significant amounts of oxygen, carbon and hydrogen.

To learn more about what Uranus and Neptune are made of, astronomers have devised models that match the physical properties that Voyager 2 and Earth-based telescopes have measured. Many models assume the planets have a thin hydrogen and helium envelope; an underlying layer of compressed, superionic water and ammonia; and a central rocky core. (The water is what gives them their "ice giant" tag.) Some estimates suggest Uranus and Neptune may each have 50,000 times the quantity of water in Earth's oceans.

But the authors of the new study say these models ignore the way the ice giants formed. As Uranus and Neptune coalesced from the dust cloud surrounding the young sun, they gobbled up, or accreted, objects called planetesimals. The team says these planetesimals resemble present-day comets such as 67P/Churyumov-Gerasimenko, which originate in the Kuiper Belt, the doughnut-shaped region of icy bodies beyond the orbit of Neptune.

Related: Where does the solar system end?

Unlike the supposedly water-rich ice giants, though, a large fraction of these planetesimal-like objects are rich in carbon. So "how is it possible to form an icy giant from ice-poor building blocks?" said Uri Malamud, the study's lead author and a planetary scientist at Technion – Israel Institute of Technology.

To resolve this apparent paradox, Malamud and his co-authors built hundreds of thousands of models of Uranus' and Neptune's interiors. The algorithm they used "starts matching a suitable composition for the surface of the planet, and it gradually works its way deeper into the central point of the planet." They considered several chemicals, including iron, water and methane, the main component of natural gas. Then, they tried to determine which model most resembled the actual ice giants in traits such as radius and mass.

Of the various models they built, the astronomers found that those with methane fit their criteria, with the methane — either in solid chunks or, given the pressure, in a mushy state — forming a thick layer between the hydrogen-helium envelope and the water layer. In some models, methane accounted for 10% of the planet's mass.

The team published their results, which have not yet been peer-reviewed, to the preprint server arXiv in March.

This methane holds the key to resolving the ice paradox. The ice could have formed when hydrogen in the growing planets chemically reacted with the carbon in the planetesimals the planets accreted, the researchers said. Such reactions happen under high temperatures and superhigh pressures — millions of times the air pressure we experience on Earth. These are the exact conditions scientists think existed in the developing planets.

The findings could provide greater insight into these little-understood planets, although verifying if they are actually rich in methane would be challenging, Malamud said. That would be a goal for one of several proposed missions from NASA and other space agencies that aim to explore Uranus.

As the solar system's planets rove around the sun, sometimes a few will appear to line up in the sky. But have all eight planets ever truly aligned?

The answer depends on how generous you are with the definition of "align" for the solar system's planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

To start with, the orbits of the planets are all tilted to different degrees with respect to the sun's equator. This means that, when planets appear to line up in the sky, in reality they are likely not positioned in a straight line in 3D space, Arthur Kosowsky, an astrophysicist at the University of Pittsburgh, told Live Science.

"The concept of planetary alignment is more about the visual appearance from our perspective on Earth rather than any significant physical alignment in space," Nikhita Madhanpall, an astrophysicist at Wits University in South Africa, told Live Science.

A planetary conjunction is when two or more planets appear close together from our perspective on Earth. It's important to note that the planets are never actually close together. Even when two planets appear lined up to a person on Earth, they are still extremely far apart in space, The Planetary Society notes.

Related: Which planet is closest to Earth? (Hint: There's more than 1 right answer.)

The definition of how close the planets can appear to be considered aligned is not well defined, Wayne Barkhouse, an astrophysicist at the University of North Dakota, told Live Science. Any such definition would involve "angular degrees," the way astronomers measure the apparent distance between two celestial objects in the sky.

If you measured the distance around the circle of the entire horizon, that would equal 360 degrees. To give an idea of the horizon's enormity, the full moon appears only half a degree across, according to Las Cumbres Observatory in Goleta, California.

In the book "Mathematical Astronomy Morsels" (Willmann-Bell, 1997), Jean Meeus, a Belgian meteorologist and amateur astronomer, calculated that the three innermost planets — Mercury, Venus and Earth — "line up within 3.6 degrees on average every 39.6 years," Barkhouse said.

Lining up more planets takes time. According to Meeus, "all eight planets will line up within 3.6 degrees, for example, every 396 billion years," Barkhouse said. "Which means it has never occurred and will not occur, since the sun will transform into a white dwarf in roughly 6 billion years from now. During this process, the sun will become a red giant and expand in size to swallow both Mercury and Venus, and probably the Earth as well. Thus, only five planets will remain in our solar system."

The chances are worse for all eight planets aligning within 1 degree of sky. According to Meeus, "this will occur, on average, every 13.4 trillion years," Barkhouse said. In comparison, the universe is about 13.8 billion years old.

If you consider the eight planets aligned if they are in the same 180-degree-wide patch of sky, the next time that will happen is May 6, 2492, according to Christopher Baird, an associate professor of physics at West Texas A&M University. The last time the eight planets were grouped within 30 degrees was Jan. 1, 1665, and the next time will be March 20, 2673, according to the National Solar Observatory's facility at Sacramento Peak, California.

Madhanpall noted that planetary alignments have virtually no significant physical effects on Earth. "The only impact to life on Earth during an alignment is the wonderful display visible in the sky," Barkhouse added. "There is no danger of enhanced earthquakes or anything like that. The change in the gravitational force that the Earth will experience due to any planetary alignment is negligible."

The solar system just got three new official residents — a trio of tiny moons, one of which orbits Uranus and two more that circle Neptune.

The three moons were all spotted several years ago but were recently confirmed by the International Astronomical Union's (IAU) Minor Planet Center — the organization responsible for naming new solar system objects such as moons, asteroids and comets. The new trio, which have been given numerical designations, will be given formal, literature and mythology-inspired names in the coming years.

Uranus' new moon, S/2023 U1, is only around 5 miles (8 kilometers) across, making it one of the smallest known moons around any of the eight planets in the solar system, alongside Mars' minute companion Deimos. The diminutive moon, which takes around 680 days to orbit around Uranus, brings the planet's total moon count to 28. Like the other Uranian moons, S/2023 U1 will eventually be named after a character from the plays of William Shakespeare, joining the likes of previously discovered moons such as Titania, Oberon and Puck.

Neptune's new satellites, S/2002 N5 and S/2021 N1, are around 14.3 miles (23 km) and 8.7 miles (14 km) wide respectively. S/2021 N1 takes around 9 years to orbit Neptune, while S/2002 N5 takes almost 27 years to orbit the furthest planet from the sun, which now has 16 known moons. Like other Neptunian moons, the newly recognized bodies will be named after the Nereids — the daughters of the sea god Nereus from Greek mythology.

The new moons were each spotted using ground-based telescopes, which is no mean feat considering their diminutive size and distance from our planet.

"The three newly discovered moons are the faintest ever found around these two ice giant planets using ground-based telescopes," Scott Sheppard, an astronomer at the Carnegie Institution for Science in Washington D.C. who was involved in all three discoveries, said in a statement. "It took special image processing to reveal such faint objects."

Related: 10 out-of-this-world solar system discoveries made in 2023

The new moons are so small and far away that their movements are normally too small to be noticeable in most ground-based images of Uranus or Neptune, especially compared to distant stars and galaxies in the background. To counteract this problem, the astronomers took long exposure images and stacked them together to create images where background objects, such as stars and galaxies, became blurred. This stacking made objects with relative motions to each planet stand out much more clearly.

This technique allowed the astronomers to "bring the moons out from behind the background noise in the images," Sheppard said.

The new trio aren't the only moons recently discovered around solar system planets. In February 2023, the IAU confirmed 12 new moons around Jupiter, bringing its total to 92 — the highest total of any planet at the time. But in May last year, the IAU confirmed a whopping 62 moons around Saturn, bringing its total to 145 and wrestling the title of most satellites back from Jupiter. A majority of these new moons, which mostly spanned just a few miles across, were also discovered using Earth-based telescopes.

The recent discoveries demonstrate how new techniques, such as the image stacking, and more powerful ground-based telescopes are allowing researchers to peer even further and with greater clarity into the outer reaches of our cosmic neighborhood.

The solar system ice giants Neptune and Uranus have finally revealed their true colors — thanks to images collected by Voyager 2 three decades ago that have been polished with data from the Hubble Space Telescope and the Very Large Telescope (VLT).

Neptune was previously thought to be a dark azure, while Uranus was supposedly a lighter blueish-green. However, the polished images reveal the ice giants are much closer in color to each other and are actually a lighter blue-green hue.

The images of Uranus, the seventh planet from the sun, and Neptune, the eighth planet, were collected in 1986 and 1989, respectively, as NASA's Voyager 2 spacecraft headed out of the solar system. A team of researchers recently reprocessed  the images, which were published Thursday (Jan. 4) in the Monthly Notices of the Royal Astronomical Society.

Related: Spiral galaxies like the Milky Way are surprisingly rare. Astronomers may finally know why.

"Applying our model to the original data, we have been able to reconstitute the most accurate representation yet of the color of both Neptune and Uranus," lead study author Patrick Irwin, a planetary physicist at the University of Oxford, said in a statement.

How Neptune and Uranus hid their true colors

Scientists knew the ice giants likely looked different than images suggested.That's because when missions like Voyager 2 — thus far the only spacecraft to visit the ice giants — observed Uranus and Neptune, they did so in single wavelengths of light at a time. As a result, all images of them were composites built from several single-color observations of the planets.

These composite images weren't always well-balanced enough to paint a true picture of the planets' colors. This was especially true in the case of Neptune. The contrast in many images of Neptune was enhanced to enable scientists to better see the bands that stretch across the ice giant, as well as its clouds and storms.

"Although the familiar Voyager 2 images of Uranus were published in a form closer to 'true' color, those of Neptune were, in fact, stretched and enhanced, and therefore made artificially too blue," Irwin said. "Even though the artificially saturated color was known at the time amongst planetary scientists — and the images were released with captions explaining it  —  that distinction had become lost over time."

Neptune is "less blue" now thanks to Hubble

To obtain true-color images of Neptune and Uranus, Irwin and colleagues turned to data collected by the Hubble Space Telescope's Imaging Spectrograph (STIS) and Wide Field Camera 3 (WFC3). The team also used data gathered by the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope (VLT) located in the Atacama Desert of northern Chile.

In the images taken by these instruments, each pixel is a continuous spectrum of colors, meaning the data they collected could be used to rebalance the composite images built by Voyager 2.

The results showed that both ice giants are a similar icy cool greenish blue, though Neptune is slightly bluer. The scientists think this is the result of Neptune having a thinner layer of haze surrounding it than Uranus does.

The research also explains why Uranus changes color slightly during its 84-Earth-year orbit of the sun. Previous observations showed that the ice giant appears a touch greener during its summer and winter solstices, when one of its poles is pointed towards the sun, than during its equinoxes, when the sun is above the ice giant's equator.

Irwin and colleagues think this is the result of a "hood" of icy methane increasing the reflection at green and red wavelengths at Uranus' poles. This hood is absent at the equator.

"This is the first study to match a quantitative model to imaging data to explain why the color of Uranus changes during its orbit," Irwin said. "In this way, we have demonstrated that Uranus is greener at the solstice due to the polar regions having reduced methane abundance but also an increased thickness of brightly scattering methane ice particles."

Heidi Hammel, vice president for science at the Association of Universities for Research in Astronomy (AURA), said the new images address lingering ice-giant puzzles.

"The misperception of Neptune's color, as well as the unusual color changes of Uranus, have bedeviled us for decades," Hammel said in the statement. "This comprehensive study should finally put both issues to rest."

Every year, we learn more about the intricacies of the solar system, and 2023 has been no different. This year, scientists shed more light on our cosmic neighborhood with some intriguing discoveries. From shrinking planets and new moons to an icy supervolcano and mysterious spots, here are the 10 wildest things we learned about the solar system in 2023. 

Mercury is shrinking 

Starting with the planet closest to the sun, Mercury, an October study revealed that the solar system's tiniest planet might be getting even smaller.

Experts have long known that Mercury has shrunk significantly since it first formed. Giant cracks, known as scarps, on the planet's surface were created as the planet contracted over long periods of cooling. 

Scientists originally thought these scarps were billions of years old, but the new research showed that some were just 300 million years old, which suggests the planet has been shrinking for most of its life — and it could still be happening today. 

This year, scientists also discovered that salty glaciers in some of Mercury's craters could provide the necessary conditions for some extreme life-forms to thrive.

Oxygen found on Venus 

Moving farther from the sun, researchers announced in November that oxygen had been detected in Venus' atmosphere for the second time, confirming that the element is present on the hellish planet. 

The thin layer of molecular oxygen (unbonded oxygen atoms) was spotted by NASA's Stratospheric Observatory for Infrared Astronomy, a telescope attached to a large plane that flew above most forms of interference in Earth's atmosphere between 2014 and 2022.

However, this oxygen is not a sign of life on Venus. Instead, researchers suspect the gas is created as solar radiation breaks down carbon dioxide and carbon monoxide molecules in the atmosphere. This oxygen would also be useless to future human colonists because it is not breathable and is found in low concentrations.

This year, scientists also discovered that Venus has thousands more volcanoes than we previously realized and that a majority of them could still be active.

The moon is older than we thought 

Closer to home, a study published in October revealed that the moon may be at least 40 million years older than we previously thought.

Researchers examined tiny impact crystals, known as zircon crystals, within lunar rock samples brought back by NASA's Apollo 17 mission. The new analysis revealed that these crystals,which were left by a colossal collision between Earth and a Mars-size planet that birthed the moon, were older than similar crystals found in other lunar samples.

"These crystals are the oldest known solids that formed after the giant impact," the researchers wrote, and they act as "an anchor for lunar chronology."

This year, astronomers also detected a mysterious heat-emitting blob on the moon's far side and spotted a separate chunk of the moon orbiting Earth.

Mars is spinning faster and faster

One of the biggest stories to come from Mars this year is that the Red Planet's spin has been getting quicker every year, and scientists don't know why.   

Data from NASA's InSight mission shows that Mars' rotation is accelerating at a rate of 4 milliarcseconds per year, which means its days are growing slightly shorter. (A milliarcsecond is one one-thousandth of an arcsecond, which is a unit of angularity.)

Two leading theories explain the speed-up. The first is that ice accumulation at the planet's poles is causing a slight change in how its mass is distributed, and the second is a phenomenon called postglacial rebound, where landmasses rise up after millennia buried under ice.

This year, scientists also solved the mystery of the planet's largest-ever "marsquake" and calculated the minimum number of people needed to start a Martian colony.

Jupiter has a dozen new moons 

This year, scientists confirmed the existence of 12 new moons around Jupiter, bringing the planet's satellite count to 92. At the time, this set a new solar system record.

The newly discovered Jovian moons are small, ranging from 0.6 to 2 miles (1 to 3.2 kilometers) wide, and most of them have wide orbits — nine of the 12 moons take more than 550 days to orbit Jupiter.

The moons were discovered in 2021 and 2022 but were just confirmed this year by the International Astronomical Union's Minor Planet Center.

This year, NASA's Juno spacecraft also discovered organic compounds on the surface of Jupiter's largest moon, Ganymede. The molecules likely came from the moon's subsurface ocean, hinting that it could sustain life.

But Saturn has even more moons

If you thought Jupiter gained lots of moons this year, just wait until you get a load of Saturn's new satellites. This year, scientists officially added 62 moons to the ringed planet's roster, bringing its total to 145 and setting a new record that is unlikely to be broken by Jupiter again. 

Some of the new moons were just 1.6 miles (2.5 km) wide. But all of the newly detected satellites are "irregular moons," meaning they follow distant, elliptical orbits around their host planet and often move in retrograde, meaning in the opposite direction of Saturn's rotation. Some are also clumped together, suggesting they were once a single body that broke apart.

This year, scientists also spotted a key organic compound shooting out of Saturn's icy ocean moon Enceladus, and researchers also worked out that the astronomer who discovered Saturn's largest moon, Titan, was probably nearsighted.  

Polar vortex spotted on Uranus 

Moving into the outer planets, new images of Uranus showed a gigantic "polar vortex" swirling around the ice giant's north pole, suggesting the planet's atmosphere is not as inert as we previously believed.

A polar vortex is a swirling ring of hot or cold air that circles a planet's polar region. These vortices have been spotted on Venus, Earth, Mars, Jupiter, Saturn and Neptune. And in 1986, NASA's Voyager 2 probe spotted a polar vortex around Uranus' south pole on its journey out of the solar system.

The swirling rings are thought to be caused by high-altitude atmospheric jet streams, although the mechanisms differ from planet to planet.

Earlier this year, scientists also spotted a polar vortex on the sun for the first time.

Neptune keeps growing mysterious spots 

This year, astronomers captured the first, clear image of one of Neptune's mysterious dark spots from Earth and photographed a never-before-seen bright spot at the same time.

Temporary dark spots have been documented on the solar system's most distant planet since 1989, when Voyager 2 spotted one as it passed by. Scientists think the dark spots are probably gigantic storms, like Jupiter's "Great Red Spot," but they are unsure why the spots appear so dark. 

The recent bright spot has never been seen before and lasted only a few weeks, so its origins are even more mysterious. But the different spots are likely linked, researchers said.

This year, astronomers also noticed that all of Neptune's clouds had suddenly vanished. The disappearing act is likely linked to a peak in solar activity as the sun reaches the explosive peak in its roughly 11-year solar cycle, known as the solar maximum. 

Pluto has an icy supervolcano 

Demoted planet Pluto has been hiding a gigantic cryovolcano the size of Yellowstone's supervolcano, an October study revealed.

Cryovolcanoes, also known as ice volcanoes, are simply volcanoes that erupt with cryomagma — ice, water and various gases — instead of molten rock. They've been found in several places across the solar system, including the dwarf planet Ceres and at the heart of explosive comets, such as the "devil comet."

Pluto's newly discovered volcano, named Kiladze Caldera, was originally pegged as a crater in images captured by NASA's New Horizons mission. But after taking a second look at the data, scientists detected traces of cryomagama around the depression, which is evidence that it has erupted multiple times.

Scientists don't know if it's still active, but if it is, it could produce enough cryomagma to cover Los Angeles.

Planet Nine might not exist (but it also might) 

Planet Nine is a hypothetical planet that is rumored to exist somewhere in the outer reaches of the solar system.

The Planet Nine hypothesis arose when astronomers detected gravitational anomalies in the Kuiper Belt — a group of comets and asteroids beyond the orbit of Neptune. These anomalies suggest that an invisible planet up to 10 times the size of Earth is lurking beyond the Kuiper Belt.

But in a preprint paper uploaded in September, scientists proposed that these gravitational anomalies could be explained by an alternative theory of gravity, known as modified Newtonian dynamics (MOND). 

MOND suggests that entities toward the edge of the Milky Way, such as the solar system, experience a greater gravitational tug from our galaxy's supermassive black hole heart than traditional gravity allows. Therefore, the Kuiper Belt object may be tugged away by our galaxy and not an elusive planet. However, MOND is not a universally accepted theory, so for now, our best guess is that Planet Nine does exist. 

When you're standing on Earth's surface, it's easy to forget that our planet is hurtling around the sun at more than 67,000 mph (107,800 km/h). And it's even easier to forget that there are seven other planets also making their way around our home star at similar breakneck speeds, or that all eight have been ceaselessly circling the solar system for billions of years. 

But what might really blow your mind is finding out how many trips around the sun each planet has under its belt. This may seem like a tricky thing to calculate, but because the planets' orbits have remained largely unaltered for most of their existence, all it takes is a bit of basic math.

Related: What's the maximum number of planets that could orbit the sun?

The solar system was born around 4.6 billion years ago, when the sun began to form from a cloud of dust left behind by prior stellar explosions. Around 4.59 billion years ago, the giant planets — Jupiter, Saturn, Uranus and Neptune — were born. And around 4.5 billion years ago, the smaller, rocky planets — Mercury, Venus, Earth and Mars — took shape, according to The Planetary Society.

But when the planets were born, their orbits around the sun were not the same as they are today (especially those of the giant planets). For around 100 million years after the first planets formed, there was a "dynamical instability" among them, which resulted in a gravitational tug-of-war between these large bodies and caused the rest of the outer solar system's planetary material, and even some emerging protoplanets, to be catapulted out of the solar system, Sean Raymond, an astronomer at the Bordeaux Astrophysics Laboratory in France and an expert on planetary systems, told Live Science in an email. 

However, once all of the planets had emerged and finished jostling with one another for their positions, they settled into consistent, stable orbits that haven't changed much since.

"For 98% to 99% of the solar system's lifetime, the planets' orbits have been nice and stable," Raymond said. As a result, you can use the planets' current orbital dynamics to make a pretty accurate guess at how many trips they have made around the sun, he added.

Take Earth, for example. Our planet takes a year to orbit the sun and has existed for 4.5 billion years, so it has taken roughly 4.5 billion trips around the solar system. 

However, the number of total orbits varies greatly among the other planets because their years are either shorter or longer than Earth's.

Mercury, the closest planet to the sun, takes only 88 days (or roughly 0.24 years, based on a year with 365.25 days) to travel around the sun once. So, over the past 4.5 billion years, it has completed around 18.7 billion solar orbits. But Neptune, the farthest planet from the sun, takes around 60,190 days (or 164.7 years) to complete an orbit, which means it has managed only about 27.9 million trips around the sun during its 4.59 billion years of existence. That means Mercury has orbited the sun around 18.7 billion times more than Neptune has.

Here is the full list of the planets, their year length and their total number of trips around the sun:

These sound like impressive numbers (and they are) but most of the planets could potentially double their number of orbits in their remaining lifetimes. 

In around 4.5 billion years, the sun will have swollen outward to reach Earth's orbit and transition into a red dwarf star, which will destroy Mercury, Venus and Earth. The other planets may live on for a time if they are not burned up but their orbits will likely be majorly altered.

Astronomers have observed a huge, mysterious dark spot on the surface of Neptune from Earth for the first time — and discovered a puzzling bright counterpart close to it. 

While scientists still don't comprehend the origins of this shadowy patch on the blue surface of the distant ice giant, new observations made using the Very Large Telescope (VLT) could help shed some light on this puzzling Neptunian feature. 

A dark spot on Neptune was first discovered by NASA's Voyager 2 spacecraft in 1989 when it flew by the eighth planet from the sun on its way out of the solar system. Dark spots on the surface of planets were familiar to astronomers already. Since the 1800s, they had been studying Jupiter's "Great Red Spot," a storm that has been raging on the gas giant for at least 200 years. The dark spot on Neptune was strange, however, because it disappeared after Voyager 2's observations. Then, in 2018, the Hubble Space Telescope detected several new Neptunian dark spots in both the planet's southern and northern hemispheres.

Related: All of Neptune's clouds have mysteriously disappeared, and the sun may be to blame

This piqued the interest of University of Oxford professor Patrick Irwin, who led a team to investigate Neptune with the VLT's Multi Unit Spectroscopic Explorer (MUSE), focusing on one of the spots in the planet’s northern hemisphere. By doing this, the researchers hoped to dismiss a previously proposed explanation, that the dark spots are caused by a clearing in clouds over the frozen surface of the ice giant.

"Dark spots are very large, 6,200 to 9,300 miles (10,000 – 15,000 km) in diameter and very mysterious,” Irwin, lead author of a paper published in the journal Science, told Live Science via email. “When the Great Dark Spot was observed by Voyager 2, there was some speculation that it might be similar to Jupiter's Great Red Spot, but we now know that Neptune's dark spots are very different. In addition to seeing a dark spot from Earth, we have also detected a deep, bright spot, labeled DBS-2019, next to the dark spot, which has never been seen before."

Still in the dark about the "spottiness" of Neptune

The team used MUSE to measure reflected light, broken down into component colors, from Neptune's dusky patch and found that this spot isn't darker than its surroundings due to the density of clouds above it. 

Instead, it is because the particles in this level of the atmosphere are themselves darker, emitting light at wavelengths of 700 nanometers  —  around the color red in the electromagnetic spectrum. 

The light spot seen by the astronomers, which is at the same level in the atmosphere as the dark spot, wasn't present in observations of Neptune conducted a few weeks before MUSE collected its data, and this seems to imply it is a short-lived feature.

"The fact that it's so close to the dark spot is interesting and suggests some connection, although what that connection is is not known," Irwin explained. 

The researchers also aren't yet sure what causes the dark spots on Neptune, but Irwin said they can put forward a few viable hypotheses for the origins of these shadowy patches. 

"We suggest it could be caused by the addition of darker particles from below," Irwin said. An alternative theory is that ultraviolet light is causing local heating, turning hydrogen sulfide ice straight from a solid to a gas, releasing a darker haze in the Neptunian atmosphere. "We need more observations and also more dynamical modeling to figure out what's going on here," Irwin added.

The ability to see features like this from Earth represents a massive step forward in planetary astronomy, but Irwin and the team now intend to look deeper with an instrument located off the surface of our planet, the James Webb Space Telescope (JWST).

"We're also part of a team set up to analyze recent observations of Neptune made with JWST," he concluded. "I can't wait to get cracking on these data!"

All of Neptune's clouds have vanished, and scientists think the sun is to blame.

The disappearance of the wispy, white strands of frozen methane that usually streak Neptune's azure face has been linked to changes in ultraviolet (UV) radiation as the sun's activity climbs to an 11-year maximum.

The clouds around the solar system's eighth and most distant planet — located roughly 2.8 billion miles (4.5 billion kilometers) from the sun — began fading in 2019 and were gone without a trace by 2020. The researchers who made the discovery will publish their findings in the Nov. 1 edition of the journal Icarus.

Related: Rare red asteroids around Neptune could reveal the secrets of the early solar system

"Even now, four years later, the most recent images we took this past June still show the clouds haven't returned to their former levels," Erandi Chavez, a graduate student at the Harvard-Smithsonian Center for Astrophysics who led the study as an undergraduate at the University of California, Berkeley, said in a statement. "This is extremely exciting and unexpected, especially since Neptune's previous period of low cloud activity was not nearly as dramatic and prolonged."

The sun's activity rises and falls in 11-year cycles, but recently, the sun has been far more active than expected, with sunspot appearances nearly double the number predicted by the National Oceanic and Atmospheric Administration's Space Weather Prediction Center. Scientists anticipate that the sun's activity, initially thought to reach its maximum in 2025, could peak as soon as the end of this year. 

Astronomers have pegged the loss of cloud cover to the effects of sunlight hitting Neptune's atmosphere. By analyzing data collected by the Hubble Space Telescope, the Keck Observatory in Hawaii, and the Lick Observatory in California, astronomers observed that, following a two-year delay, peaks in the sun's activity generate more cloud cover over Neptune, while lows cause it to dissipate.

What, exactly, is causing the change isn't known for certain. The most likely explanation is that UV light from the sun starts chemical reactions in Neptune's upper atmosphere, ultimately creating the clouds.

"It's fascinating to be able to use telescopes on Earth to study the climate of a world more than 2.5 billion miles away from us," study co-author Carlos Alvarez, a staff astronomer at the Keck Observatory, said in the statement. "Advances in technology and observations have enabled us to constrain Neptune's atmospheric models, which are key to understanding the correlation between the ice giant's climate and the solar cycle."

Astronomers have finally peered past the clouds on the exoplanet GJ 1214b, a mini-Neptune planet around a star about 40 light-years away. Mini-Neptunes, like a shrunken down version of the familiar gas giant, are a common type of planet in our galaxy — but because there isn't one in our own solar system, these worlds have largely remained a curiosity for scientists.

Previous observations of the distant planet were foiled by thick cloud layers, but the powerful James Webb Space Telescope's (JWST) infrared heat vision allowed astronomers to find a new view through the haze. The results, published May 10 in the journal Nature, reveal that GJ 1214b has an atmosphere made of steam, hinting at its past as a possible "water world," according to NASA researchers. 

Related: 35 Jaw-dropping James Webb Space Telescope images

"For the last almost decade, the only thing we really knew about this planet was that the atmosphere was cloudy or hazy," Rob Zellem, an exoplanet researcher at NASA's Jet Propulsion Lab, said in a statement. The team used JWST's Mid-Infrared Instrument (MIRI) to map the temperature of the planet as it moved through its orbit, capturing information on both its day and night sides and enabling astronomers to figure out what it's made of.

The temperature on GJ 1214b shifted dramatically from day to night, getting as hot as 535 degrees Fahrenheit (280 degrees Celsius) and then cooling down by more than 100 degrees F at night. Imagine a day on Earth with sweltering heat during the day, and then a blizzard overnight — that's what a 100-degree difference would look like here! On GJ 1214b, this huge temperature swing indicates that the planet's atmosphere can't be just light hydrogen molecules; instead, there has to be something else like water or methane. Researchers see this finding as an interesting clue into the planet's past, since the atmosphere doesn't match what the star is made of.

GJ 1214b "either lost a lot of hydrogen, if it started with a hydrogen-rich atmosphere, or it was formed from heavier elements to begin with — more icy, water-rich material," lead study author Eliza Kempton, a University of Maryland astronomer, said in the statement. "The simplest explanation, if you find a very water-rich planet, is that it formed farther away from the host star," she added.

Astronomers still have a lot left to figure out about GJ 1214b, but they hope to observe more mini-Neptunes with JWST in the near future. According to Kempton, they hope to figure out a "consistent story" for how mini-Neptunes are created, and how this particular one ended up with so much water.

Neptune is famously a vivid blue, but the asteroids orbiting near it are decidedly not. An international team of astronomers recently took a peek at Neptune's Trojan asteroids and found that they all seem to be some shade of red — far redder than most asteroids in the solar system. They published their results Feb. 14 in the journal Monthly Notices of the Royal Astronomical Society: Letters.

The Neptunian Trojans are a cloud of asteroids whose orbit around the sun parallels Neptune's. They hang out in the gravitationally stable points between Neptune and the sun, or between Neptune and the dwarf planet Pluto. First discovered in 2001, fewer than 50 of these rocky bodies have been described to date. 

The reason for this is not that Neptunian Trojans are rare; it's probably because it's difficult to spot space rocks that are so small and far away. These asteroids tend to be 31 to 62 miles (50 to 100 kilometers) across and orbit at a distance of 2.8 billion miles (4.5 billion km) from the sun. Prior to this research, astronomers had studied only a baker's dozen of these asteroids, and had to use some of Earth's largest and most powerful telescopes to do it. 

"In our new work, we have more than doubled the sample of Neptunian Trojans studied with large telescopes," Bryce Bolin, an astronomer at NASA's Goddard Space Flight Center and lead author of the study, said in a statement.

Bolin's team synthesized data collected by four telescopes — the Palomar Observatory telescope in California, the Gemini North and South telescopes in Hawaii and Chile and the Keck telescope in Hawaii — over two years. Researchers tracked 18 Neptunian Trojans and analyzed their color. They found that most were significantly redder than most asteroids, including four that were extremely red.

That crimson color indicates that the Neptunian Trojans are rich in volatile compounds such as ammonia and methanol. Ices made of these chemicals are very sensitive to heat and will rapidly turn to gas when exposed to enough solar radiation. Because of this, astronomers expect that asteroids closer to the sun to have far less of a red tinge; their ammonia and methanol have already boiled away. 

Sure enough, researchers have observed a sort of ombré progression of red asteroids, starting with slate gray rocks in the inner solar system and working out to dark red beyond Pluto's orbit.   

It's likely that some of Neptune's reddest asteroids formed even farther from the sun in the solar system's early days, before migrating inward and getting caught in Neptune's orbit, the researchers added. Studying them could open a window into how asteroids in the early solar system formed and how their composition has changed over the past 4.6 billion years.

Astronomers have discovered an entirely new ring system within the solar system, and it's located at such a great distance from its dwarf planet parent that it should be impossible. 

The ring surrounds Quaoar, which is around half the size of Pluto and located beyond Neptune. It is only the third ring to be found around a minor planet and the seventh ring system in the solar system, with the most famous and well-studied rings surrounding the giant planets Saturn, Jupiter, Neptune and Uranus.

"The six [previously known] planets with ring systems all have rings which are quite close to the surface of the planet. So this really challenges our ring formation theories," study co-author Vik Dhillon, a professor of physics and astronomy at the University of Sheffield in England, told Live Science. "It was previously thought to be impossible to have rings that far out, so in a nutshell, the ring of Quaoar is a real challenge to explain theoretically."

Related: Ghostly rings of Neptune shine in new James Webb Telescope images

The ring system is located at a distance of seven planetary radii away from Quaoar (that is, seven times Quaoar's radius), which is twice as far out as the theoretical maximum limit for a ring system, known as the Roche limit. For comparison, the main part of Saturn's rings sits at just three planetary radii from the gas giant. 

Previously, it was thought that rings past the Roche limit wouldn't be able to survive this far out from their parent body. 

"Rings that are formed outside Roche limits aren't meant to be stable; they should rapidly accrete into moonlets, using up all the ring material," Dhillon said. "With this discovery, we have a ring not just outside the Roche limit, but way beyond it."

The team's findings were published Feb. 8 in the journal Nature.

How a dwarf planet grew a distant ring

Dhillon and the team think Quaoar's ring formed similarly to other solar system rings: Collisions of moonlets orbiting the parent planet created debris that settled into a ring made of rock, ice and dust particles. 

These particles can't reform a moonlet if they are close to the planet and within the Roche limit, because tidal forces from the parent body constantly rip them apart and prevent them from clumping, according to the researchers. But that can't be the case with Quaoar's ring.

"We've got to find some way of stopping that moonlet forming that far out," Dhillon said. "The particles in the ring are colliding all the time, and if these collisions are elastic, it means the particles can't stick together to form a moonlet." (An elastic collision is one in which two colliding objects bounce away from each other rather than clumping together, like a rubber ball hitting a floor.)

Elastic collisions may be possible if the ring particles have an icy outer coating, Dhillon said — something that is plausible, given Quaoar's location at the edge of the solar system. However, more data are needed to confirm this idea. 

A chance discovery

The researchers discovered the ring system while  investigating whether Quaoar has an atmosphere. The team used the high-speed HiPERCAM instrument on the Gran Telescopio Canarias), a telescope in Spain's Canary Islands that can spot small variations in light from background stars. The ring became visible when it caused a roughly 5% to 10% dip in light from a background star, both before and after  the main body of Quaoar passed in front of the star. This event, known as an occultation, lasted less than a minute.

"The discovery came as a bit of a surprise," Dhillon said. "We knew there was a possibility we might find them, but we weren't really looking for them."

The ring of Quaoar is too small and too faint to be seen via direct imaging, even with an instrument as powerful as the Hubble Space Telescope. Dhillon added that other than occultation events, the only way to spot these dwarf planet rings would be to send a robotic probe to visit them. 

"This discovery shows you the amazing diversity of things that are in our own cosmic backyard," Dhillon said. "You don't have to look light-years away into the distant universe to find the unexpected. Surprises are still aplenty in our own solar system."

Archaeologists in war-torn Syria have unearthed a stunning mosaic from the Roman era that features events from the Trojan War, the chiseled muscles of the Roman demigod Hercules and the powerful ancient Roman god Neptune alongside 40 of his mistresses.  

The General Directorate of Antiquities and Museums, a Syrian government agency, discovered the 65.5-foot-long by 20-foot-wide (20 by 6 meters) mural in Rastan, a town in central Syria near Homs, a key battleground during the Syrian revolution, agency representatives announced on Wednesday (Oct. 12), according to the Associated Press (AP). 

The agency uncovered the well-preserved mural — painstakingly made in ancient times with colorful stones that each measured just 0.5 by 0.5 inches (1.2 by 1.2 centimeters) across — in a building that was held by civil war rebels until 2018, when Syrian government forces took the town, according to the BBC. The ancient ruins under the building are still undergoing excavation.

"We can't identify the type of the building, whether it's a public bathhouse or something else, because we have not finished excavating yet," Humam Saad, the associate director of excavation and archaeological research at the directorate, told the AP.

Related: UK man stumbles upon 800-square-foot Roman mosaic on his father's farm

The mural is a rare find that is "rich in details," and is easily the most important archaeological find in the country since the civil war started in 2011 during the Arab Spring, Saad added. 

The mural dates to the fourth century A.D., after the Western Roman Empire split from the Eastern Roman Empire (also known as the Byzantine Empire). Businessmen from Lebanon's Nabu Museum had originally purchased the building, and then donated it to the Syrian state, the AP reported.

The mural includes depictions of the Trojan War, a legendary war fought between the Greeks and Trojans in ancient Troy (modern-day Turkey), as described in the epic poems "The Iliad" and "The Odyssey," by Homer.

The mural also shows Hercules (known as Heracles to the Greeks) slaying Hippolyta, the queen of the Amazon warriors, after he went to retrieve her belt as the ninth of his 12 labors.

Many of Syria's artifacts have been destroyed and looted during the past 11 years of conflict. During its excavation, the mosaic faced an uncertain future

"Unfortunately, there were armed groups that tried to sell the mosaic at one point in 2017 and listed it on social media platforms," Saad told the AP.

When it comes to planetary rings, Saturn is the undisputed poster child. But now a new contender enters the, er, ring — courtesy of a stunning new image taken by the James Webb Space Telescope (JWST).

In the new picture, released today (Sept. 21) by the European Space Agency (ESA), our solar system's eighth planet Neptune shimmers like a glorious crystal ball, with a stack of gauzy rings wrapped magically around it.

Astronomers have known for several decades that the ice giant, located about 30 times farther from the sun than Earth, has five rings made chiefly of icy dust. The new image reveals those frigid rings in crisper detail than any survey has since the Voyager 2 probe passed within a few thousand miles of Neptune in 1989, according to the ESA.

"In addition to several bright narrow rings, the Webb images clearly show Neptune's fainter dust bands," ESA researchers wrote in a statement. "Webb's extremely stable and precise image quality permits these very faint rings to be detected so close to Neptune."

Floating near the edge of our solar system, Neptune is a world of near-permanent twilight, invisible to the naked eye. But in visible light images taken by Voyager 2 and the Hubble Space Telescope, Neptune appears a striking blue.

That coloration comes from methane in the planet's cloudy atmosphere, which likely stretches down to great depths within the planet before melding into a super-hot ocean of melted ice, ammonia and other compounds, according to NASA. To the JWST, which uses a special sensor to capture light at near-infrared wavelengths, those methane clouds shine eerily with reflected sunlight, giving the planet a more ghostly, white appearance.

Another striking feature in the new JWST image are Neptune's moons. Seven of the planet's 14 known moons are on display here, including its largest, Triton — seen as the severely spiky point of light in the upper left corner. While it looks like a bright star, Triton is actually just an extremely reflective, icy rock.

"Covered in a frozen sheen of condensed nitrogen, Triton reflects an average of 70 percent of the sunlight that hits it," according to the ESA. "It far outshines Neptune because the planet's atmosphere is darkened by methane absorption at Webb's wavelengths."

The JWST commenced operations on July 12, and has already released an array of spellbinding images of the cosmos, focusing on objects both near to Earth and mind-bogglingly far away. The telescope will continue observing both Neptune and Triton in the coming year, according to the ESA.

Originally published on Live Science.

Neptune is the farthest planet from the sun and one of two "ice giants" in our solar system. The cold, blue planet is about 30 times farther away from the sun than Earth and takes around 165 Earth years to complete a single orbit around our star. Neptune spins around its axis quicker than Earth, so a day on Neptune is only around 16 Earth hours.

When was Neptune discovered?

Scientists discovered Neptune in 1846, after they conducted orbit calculations for Uranus that indicated there was an unknown planet affecting Uranus's gravity, according to the Natural History Museum in London, U.K. Neptune isn't visible to the naked eye, but the researchers were able to confirm the planet's existence using a telescope. Astronomers had previously spotted Neptune through telescopes as early as 1612, but hadn't identified it as a planet, according to NASA. 

Only one of Earth's probes has ever reached Neptune — Voyager 2, which snapped the first images of the blue planet in 1989 on its way out of the solar system. Neptune appears blue, or blue-green, because of the methane in its atmosphere, according to Smithsonian National Air and Space Museum in Washington D.C. The name Neptune comes from the Roman god of the sea of the same name, according to Cool Cosmos, a website run by the Infrared Processing and Analysis Center at the California Institute of Technology. 

Related: Mercury probe snaps stunning photos of our planet during Earth flyby 

How long would it take to get to Neptune?

Neptune is the eighth planet from the sun and the final planet in the solar system, since scientists demoted Pluto from full planetary status to dwarf planet in 2006. Neptune is also the farthest planet in the solar system from Earth and orbits at a distance of between 2.7 billion miles (4.3 billion kilometers) and 2.9 billion miles (4.7 billion km) from our planet, depending on where the two planets are in their orbits, Live Science's sister site Space.com previously reported. The Voyager 2 probe took 12 years to reach Neptune, according to NASA's Jet Propulsion Laboratory. However, the probe was traveling at an average speed of 42,000 mph (about 68,000 km/h) — much faster than humans have ever traveled.

How cold is Neptune?

The temperature in Neptune's atmosphere is around minus 373 degrees Fahrenheit (minus 225 degrees Celsius), according to the National Air and Space Museum. Being farther away from the sun than Uranus, you might expect Neptune to be colder, but the two planets are about the same temperature. Neptune emits more than twice as much heat as it absorbs from the sun, similar to Jupiter and Saturn, Live Science previously reported. 

"The extra heat source on Neptune [and Jupiter and Saturn] is largely due to gravitational contraction," Joshua Tollefson, a data scientist formerly at the University of California, Berkeley, told All About Space magazine in 2019. "As the planet slowly gravitationally contracts, the material falling inward changes its potential energy into thermal energy, which is then released upwards out of the planet."

Neptune also has the strongest winds in the solar system, which can reach 1,200 mph (1,9301 km/h), according to Cool Cosmos. Seasons on Neptune last about 40 years each, and the planet's southern hemisphere is currently in the Earth equivalent of summer. However, a 2022 study published in The Planetary Science Journal used infrared images of the planet to determine that despite entering summer in 2005, Neptune's global temperature actually dropped by 14.4 F (8 C) between 2003 and 2018. The researchers speculated that the plummeting temperatures in Neptune's atmosphere could be caused by either an unidentified element, extreme weather or changes in solar radiation. 

"I think Neptune is itself very intriguing to many of us because we still know so little about it," study lead author Michael Roman, an astronomer at the University of Leicester in the U.K., said in a statement at the time. "This all points towards a more complicated picture of Neptune’s atmosphere and how it changes with time."

Related: The sun has blasted Mercury with a plasma wave

What is Neptune made of?

Neptune is mostly composed of water, ammonia and methane and could be hiding a "super hot" ocean under its chilly clouds, according to NASA. The planet doesn't have a solid surface, but does have a solid core like Earth. Along with Uranus, Neptune is called an "ice giant." The name distinguishes Neptune from the "gas giants" of Jupiter and Saturn because Neptune and Uranus have more ice-forming molecules, according to the Planetary Society.

Neptune and Uranus are famous for their "diamond rain." This is possible because the high atmospheric pressure on these planets — which is more than 200,000 times what it is on Earth — breaks up methane in the atmosphere to release carbon. The carbon then groups together in long chains to form crystalline patterns like diamonds. These "diamonds" sink through the mantle, where they are vaporized by even more extreme conditions — the innermost regions of these planets’ mantles likely hit around 12,140 F (6,727 C) with pressures 6 million times that of Earth — before floating back up for the process to repeat, Live Science previously reported.   

Does Neptune have moons?

Neptune has 14 moons and at least five rings. Triton, the largest of Neptune's moons, orbits in the opposite direction to the planet's spin. This reverse orbit indicates that Triton hasn't always been paired with Neptune, and scientists think it was pulled into Neptune's gravity from the Kuiper Belt millions of years ago, according to NASA.

Nereid, another of Neptune's moons, has an even more peculiar orbit, making it one of the weirdest moons in the solar system. This moon can swing in close to Neptune at a distance of 870,000 miles (1.4 million km) and swing out as far as 6 million miles (9.7 million km). One reason for this strange lunar orbit could be that when Triton was pulled toward Neptune, it threw off the orbits of Neptune's existing moons and sent most of them whizzing off into space. However, Nereid could be an original moon that clung on to the edge of Neptune's gravity to shape its current orbit.

Related: Neptune's wobbling moons are locked in a never-before-seen orbital dance 

Additional resources

To view images of Neptune taken by the Voyager 2 probe, check out NASA's Jet Propulsion Laboratory website. To learn more about diamond rain on Neptune and Uranus, watch this short YouTube video by astrophysicist and Live Science contributor Paul M. Sutter. For a children's book on Neptune, check out "The Secrets of Neptune" (Capstone Press, 2015).

Editor's note: This article was updated on Wednesday, May 25 at 9:00 a.m. EDT to note that Neptune, not Mercury, was analyzed in a 2022 study in The Planetary Science Journal.

Originally published on Live Science.

Astronomers have discovered a perplexing trend in Neptune's atmosphere: Ever since the planet's southern hemisphere summer began almost two decades ago, atmospheric temperatures in this region have plummeted, and scientists aren't sure why.

Neptune is the most distant planet in the solar system, around 30 times farther from the sun than Earth is. Just like every other planet orbiting the sun, Neptune has four distinct seasons: spring, summer, fall and winter. However, because Neptune takes around 165 years to orbit the sun, each of these seasons lasts around 40 years. Neptune's southern hemisphere has been experiencing summer, the period when it is tilted toward the sun, since 2005.

In a new study, researchers compiled infrared images of Neptune taken by a variety of ground and space based telescopes between 2003 and 2020. The team initially expected that temperatures in Neptune's southern hemisphere would increase as it entered summer. However, the images revealed that atmospheric temperatures in the southern hemisphere had dropped by 14.4 degrees Fahrenheit (8 degrees Celsius) between 2003 and 2018.

"This change was unexpected," lead author Michael Roman, an astronomer at the University of Leicester in the U.K., said in a statement. "Since we have been observing Neptune during its early southern summer, we expected temperatures to be slowly growing warmer, not colder."

Related: 'Diamond rain' on Uranus and Neptune seems likely 

Moreover, in the last two years of the study, temperatures around Neptune's south pole rose by 19.8 F (11 C) between 2018 and 2020. The researchers were puzzled by rapid and intense temperature change and cannot explain why this hotspot is bucking the overall trend in the southern hemisphere.   

"Our data cover less than half of a Neptune season," co-author Glenn Orton, a planetary scientist at NASA's Jet Propulsion Laboratory in California, said in the statement, "so no one was expecting to see large and rapid changes."

This is not the first time that Neptune's atmospheric temperatures have perplexed scientists. In 1989, NASA's Voyager 2 probe passed by Uranus and Neptune on its way out of the solar system and found that Neptune was warmer than its closest neighbor despite being farther away from the sun. Scientists have since discovered that this is likely due to gravitational differences between the two planets, Live Science previously reported. 

The researchers don't yet know what is causing the newly detected temperature fluctuations in Neptune's atmosphere, but they offered some potential explanations.

One possible reason is a change in atmospheric chemistry. Neptune's atmosphere is made mainly of hydrogen, as well as helium and methane. The methane gives Neptune and neighboring Uranus their blue color. However, Neptune's striking hues are more intense than those of Uranus, which likely means that another unidentified chemical lurks in Neptune's atmosphere, according to NASA. This mysterious compound or changes in the abundance of other elements could be responsible for these temperature changes, according to the statement. 

Extreme weather could also affect temperatures. Neptune has the strongest winds in the solar system; they can reach up to 1,200 mph (1,931 km/h), according to NASA. These winds push gusts of frozen methane through the planet's atmosphere, potentially affecting the temperature. Neptune also has frequent and massive storms. In 1989, Voyager 2 detected a massive storm near the planet's south pole. At its largest, the storm, known as the Great Dark Spot, was bigger than Earth, and  disappeared in 1994. 

The temperature changes may also result from the solar cycle, the researchers said. Every 11 years, the sun's magnetic field flips, altering levels of solar radiation, which scientists can measure by counting sunspots. There is a loose correlation between the temperature changes and the number of sunspots on the sun over time, but the relationship between the two is not strong enough to conclusively support this idea, according to the new study. 

Continued monitoring by ground-based telescopes and future surveys using NASA's new James Webb Space Telescope could shed light on this phenomenon, according to the statement. But for now, it remains a mystery.  

"I think Neptune is itself very intriguing to many of us because we still know so little about it," Roman said in the statement. "This all points towards a more complicated picture of Neptune’s atmosphere and how it changes with time."

The study was published April 11 in The Planetary Science Journal.

Originally published on Live Science.

The ice giants Uranus and Neptune don't get nearly enough press; all the attention goes to their larger siblings, mighty Jupiter and magnificent Saturn. 

At first glance, Uranus and Neptune are just bland, boring balls of uninteresting molecules. But hiding beneath the outer layers of those worlds, there may be something spectacular: a constant rain of diamonds.

Related: Icy planets' diamond rain created in laser laboratory

"ice giants" may conjure the image of a Tolkien-esque creature, but it's the name astronomers use to categorize the outermost planets of the solar system, Uranus and Neptune.

Confusingly, though, the name has nothing to do with ice in the sense you would normally recognize it — as in, say, ice cubes in your drink. The distinction comes from what these planets are made of. The gas giants of the system, Jupiter and Saturn, are made almost entirely of gas: hydrogen and helium. It's through the rapid accretion of those elements that these huge planets managed to swell to their current size.

In contrast, Uranus and Neptune are made mostly of water, ammonia and methane. Astronomers commonly call these molecules "ices," but there really isn't a good reason for it, except that when the planets first formed, those elements were likely in solid form. 

Into the (not so) icy depths

Deep beneath the green or blue cloud tops of Uranus and Neptune, there's a lot of water, ammonia and methane. But these ice giants likely have rocky cores surrounded by elements that are probably compressed into exotic quantum states. At some point, that quantum weirdness transitions into a super-pressurized "soup" that generally thins out the closer you get to the surface.

But truth be told, we don't know a lot about the interiors of the ice giants. The last time we got close-up data of those two worlds was three decades ago, when Voyager 2 whizzed by in its historic mission.

Since then, Jupiter and Saturn have played host to multiple orbiting probes, yet our views of Uranus and Neptune have been limited to telescope observations.

To try to understand what's inside those planets, astronomers and planetary scientists have to take that meager data and combine it with laboratory experiments that try to replicate the conditions of those planets' interiors. Plus, they use some good old-fashioned math — a lot of it. Mathematical modeling helps astronomers understand what's happening in a given situation based on limited data.

And it's through that combination of mathematical modeling and laboratory experiments that we realized Uranus and Neptune might have so-called diamond rain.

Related: Amazing photos of monster storm in Saturn's atmosphere

It's raining diamonds

The idea of diamond rain was first proposed before the Voyager 2 mission which launched in 1977. The reasoning was pretty simple: We know what Uranus and Neptune are made of, and we know that stuff gets hotter and denser the deeper into a planet you go. The mathematical modeling helps fill in the details, like that the innermost regions of the mantles of these planets likely have temperatures somewhere around 7,000 kelvins (12,140 degrees Fahrenheit, or 6,727 degrees Celsius) and pressures 6 million times that of Earth's atmosphere.

Those same models tell us that the outermost layers of the mantles are somewhat cooler — 2,000 K (3,140 F or 1,727 C — and somewhat less intensely pressurized (200,000 times Earth's atmospheric pressure). And so, it's natural to ask: What happens to water, ammonia and methane at those kinds of temperatures and pressures?

With methane, in particular, the intense pressures can break the molecule apart, releasing the carbon. The carbon then finds its brethren, forming long chains. The long chains then squeeze together to form crystalline patterns like diamonds.

The dense diamond formations then drop through the layers of the mantle until it gets too hot, where they vaporize and float back up and repeat the cycle — hence the term "diamond rain."

Lab-grown diamonds

The best way to validate this idea would be to send a spacecraft toUranus or Neptune. That won't be an option anytime soon, so we have to go with the second-best way: laboratory experiments.

On Earth, we can shoot powerful lasers at targets to very briefly replicate the temperatures and pressures found inside the ice giants. One experiment with polystyrene (aka Styrofoam) was able to make nano-sized diamonds. No, Uranus and Neptune don't contain vast quantities of polystyrene, but the plastic was much easier than methane to handle in the laboratory and, presumably, behaves very similarly.

Also, Uranus and Neptune can keep up those pressures for a lot longer than a laboratory laser, so the diamonds could presumably grow to be a lot larger than nano-sized.

The end result? Based on everything we know about the composition of the ice giants, their internal structures, results from laboratory experiments and our mathematical modeling, diamond rain is a very real thing.

Paul M. Sutter is an astrophysicist at SUNY Stony Brook and the Flatiron Institute, host of "Ask a Spaceman" and "Space Radio," and author of "How to Die in Space."

Learn more by listening to the "Ask A Spaceman" podcast, available on iTunes and askaspaceman.com. Ask your own question on Twitter using #AskASpaceman or by following Paul @PaulMattSutter and facebook.com/PaulMattSutter.

The NASA Lucy mission is an incredible space expedition that will explore the history of the solar system and reveal more about life on Earth.

The NASA Lucy launch took place on Oct. 16, 2021, and the spacecraft will fly 445 million miles away from Earth to explore swarms of asteroids that orbit the sun in two groups — one ahead of Jupiter, and one behind, according to NASA. They're called the Trojan asteroids, and no spacecraft ever paid them a visit.

These asteroid clusters have been orbiting the Sun for billions of years, and NASA's pre-mission tests show that they're probably made from the same ancient material that originally formed planets like Jupiter, Neptune and Saturn. In lunar terms, they're simple, but they’re time capsules that could give humanity some incredible insights into the birth of the solar system and the formation of life. 

Related: What's the difference between asteroids, comets and meteors?

What's the NASA Lucy mission plan?

The NASA Lucy mission's sheer distance means it’s a long-term journey — the probe will fly past Earth on Oct. 15, 2022 and use our planet's gravitational pull in several different phases so it can be flung towards the Trojan clusters, according to NASA. 

Lucy will arrive at the main solar system’s asteroid belt in April 2025, and it’ll analyze seven different Trojan asteroids between 2027 and 2033. And then, in March 2033, the Lucy mission will end. But Lucy won’t stop there – it will continue its solar orbit for millions of years.

NASA first mooted Lucy in 2015, and it was formally picked as a viable mission in 2017. Its first designs were approved in 2018, and it began assembly and testing in August 2020. The final NASA Lucy spacecraft arrived at Kennedy Space Center in Florida in July 2021 ahead of the autumn launch period, according to NASA’s Lucy mission webpage.

Lucy might seem an odd name for a space mission, but it's named after a fossilized skeleton called Lucy that was discovered in Ethiopia in 1974. That fossil is around 3 million years old, and it taught us loads of new things about the evolution of humanity, according to Arizona State University. So it's a fitting name for a space mission that NASA hopes will lead to similar discoveries from interstellar fossils.

Related: The James Webb Space Telescope: Origins, design and mission objectives

What will the NASA Lucy spacecraft test?

The NASA Lucy spacecraft will fly past seven Trojan asteroids and carry out remote testing with its range of advanced instruments. NASA plans to examine the geology on the surface of each asteroid to check out their age, structure and shape, and other tools will check each asteroid for minerals, ice and organic materials, according to NASA’s Lucy mission webpage. 

Other tools will measure the mass and density of each asteroid and will map their interior structures, too. 

NASA doesn’t quite know what Lucy will find — after all, no mission has ever been there. But the mission will supply vital information about the formation of our solar system, and this sort of exploration is a vital part of scientific discovery. 

Gravitational pull: Exploring Lucy’s orbits

The NASA Lucy spacecraft uses solar energy for power in deep space, but it will orbit Earth, Mars and the sun and rely on their gravitational pull to start its journey to the outer reaches of space, according to NASA’s Lucy mission webpage.

Lucy’s first task is to orbit the sun, and by October 2022 it'll hurtle back toward Earth and get a gravity-assisted boost that will speed up the spacecraft. This speed will take Lucy on a two-year orbit around Mars before it comes back to Earth in 2024 for another shot of gravitational help.

It’s this second shove that will propel Lucy toward the solar system’s main asteroid belt — and, beyond that, to the first cluster of Trojan asteroids. Once it has looped around those, Lucy will head back to Earth for its third gravitational boost, and this will push the spacecraft in the opposite direction, toward the second group of Trojan satellites.

Targets of the Lucy mission

Target 1: (52246) Donaldjohanson 

Lucy's smallest target is in the solar system's main asteroid belt, not the Trojan clusters. The target is 130 million years old, and NASA will use this asteroid to test Lucy's instruments. Estimated fly-by date: April 20, 2025

Target 2: (3548) Eurybates 

NASA suspects that this asteroid shares the same materials as some meteorites on Earth, and Eurybates has its own satellite — so Lucy can study two asteroids in the same visit.  Estimated fly-by date: Aug. 12, 2027

Target 3: (15094) Polymele 

This is Lucy's smallest target, at 13 miles (21 kilometers) across, and NASA believes that it's rich in organic material, and worth studying for insights into how life formed in the solar system. Estimated fly-by date: Sept. 15, 2027

Target 4: (11351) Leucus 

This slow-rotating asteroid has a day that lasts for 446 hours, and that slow day means it has huge temperature variations — so NASA can learn loads about the materials inside. Estimated fly-by date: April 18, 2028

Target 5: (21900) Orus 

This asteroid is similar to Leucus, so NASA hopes that tests on Orus will reveal more about the similar organic and carbon-based materials found here. Estimated fly-by date: Nov. 11, 2028

Target 6: (617) Patroclus and Menoetius 

These large, paired asteroids are thought to be left over from the early days of the solar system, and NASA reckons they will provide information about how planets were formed. Estimated fly-by date: March 3, 2033

Additional resources

• NASA: Solar System Exploration 
• Our Solar System: An Exploration of Planets, Moons, Asteroids, and Other Mysteries of Space by Lisa Reichley
• Asteroids (Kosmos) by Clifford J. Cunningham

A recent discovery of giant ammonia-rich hailstones, dubbed mushballs, on Jupiter might explain why Uranus and Neptune seem to have no ammonia in their atmospheres. 

Scientists have puzzled for years over the apparent absence of ammonia in the atmospheres of Uranus and Neptune.

Known for its unpleasant smell, ammonia is rather common in the universe. Since the atmospheres of Uranus and Neptune are rich in other chemical compounds known to be present in the primordial cloud from which planets formed, scientists had no good explanation for ammonia's absence in the ice giants' air. 

Related: Could a spaceship fly through a gas giant like Jupiter?

However, a recent discovery of giant ammonia-rich hailstones on Jupiter might shed some light on this mystery. Spoiler alert! The ammonia might not be missing at all; it may just be hidden in deeper layers of the planets' atmospheres, where current scientific instruments cannot reach. 

A possible key to solving this mystery was provided by NASA's Juno mission, which is currently orbiting Jupiter. 

"The Juno spacecraft has shown that in Jupiter, ammonia is present in abundance, but generally much deeper [in the atmosphere] than expected," Tristan Guillot, a researcher at the French National Centre for Scientific Research (CNRS) in Nice, said in a statement.

A study published last year in the journal Nature found that mushballs containing ammonia form high in the atmosphere of Jupiter during thunderstorms thanks to ammonia's ability to melt ice into liquid water even in extremely cold temperatures of around minus 162 degrees Fahrenheit (minus 90 degrees Celsius). 

As these mushballs fall through the atmosphere, they absorb more and more ammonia, eventually accumulating up to 2.2 pounds (1 kilogram) of mass. The ammonia gets transported deep into the atmosphere, where it remains locked below the cloud base. 

"What we have learned at Jupiter can be applied to provide a plausible solution to this mystery at Uranus and Neptune," said Guillot, who presented his theory at Europlanet Science Congress (EPSC) 2021, which was held virtually this year from Sept. 13 to Sept. 24. 

"Thermodynamic chemistry implies that this process is even more efficient in Uranus and Neptune, and the mushball seed region is extended and occurs at greater depths," Guillot added. 

That means that, just like on Jupiter, on Uranus and Neptune ammonia may be simply hidden deep in the atmosphere. Scientists currently measure the atmospheric composition of these distant planets of the solar system by analyzing the infrared and radio signatures of the atmospheres by Earth-based telescopes. 

Both of these planets have so far been visited very briefly by only one spacecraft: NASA's Voyager 2 in the late 1980s. 

The intrigues of the distant planets' atmospheres, Guillot suggests, provide an incentive for a dedicated mission that could enable scientists to fully uncover what's going on.

"To fully understand the processes, we need a dedicated mission to map the deep atmospheric structure and understand mixing in hydrogen atmospheres," said Guillot. "Neptune and Uranus are a critical link between giant planets, like Jupiter and Saturn, and ice giant exoplanets that we are discovering in the galaxy. We really need to go there!"

Follow Tereza Pultarova on Twitter @TerezaPultarova. Follow us on Twitter @Spacedotcom and on Facebook. 

Our solar system is home to some weird and wonderful weather, with storms more terrifying in scale than anything in Earth's recorded history. From centuries-old hurricanes on Jupiter to immense winds on Neptune, if you leave Earth you'll be shocked by what you find.

On Mars you will find immense dust storms that cover the entire planet, while Venus has an incredibly thick and fast-moving atmosphere that can form permanent vortices at its poles. On Jupiter and Saturn there are some huge storms — bigger than the diameter of multiple Earths — that have raged for decades or even centuries. On the ice giant Neptune you'll find the fastest winds in the solar system, and within Neptune and Uranus it may rain diamonds.

Thanks to recent missions into space, we have learned more about these fascinating weather systems than ever before. Scientists are also performing long-term studies of weather systems, such as storms erupting from the Sun that can have direct effects on Earth. As we continue to reach into the unknown, who knows what else there is to discover in the solar system?

Jupiter's Great Red Spot: An Earth-sized hurricane

This iconic storm has been raging on Jupiter for centuries, but it may not be around forever. The giant spinning storm is comparable to a hurricane on Earth, although it is considerably larger. It measures about 10,000 miles (16,000 kilometers across), which is roughly 1.3 times the width of our planet. Scientists think its roots go up to 100 times deeper into Jupiter than Earth's oceans. Recent evidence, however, suggests the storm may be shrinking, although it can devour other storms to gain a boost.

That's not the only extreme weather on Jupiter: Its north and south poles have strange arrays of cyclones arranged in a circle, while the intense radiation from the planet bathes some of its moons, such as Io and Europa.

NASA's Juno spacecraft, which entered orbit around Jupiter in 2016, has been collecting incredible data about this gas giant using an array of instruments. This includes a microwave radiometer to measure the deep atmosphere of Jupiter, ultraviolet and infrared cameras to take images of the planet's atmosphere and its aurorae, and JunoCam, which has also been busy snapping visible light images. 

Saturn's lightning: 10,000 times more powerful than Earth's

Amazingly we've not only seen lightning on Saturn, but we've also heard it. NASA's Cassini spacecraft, which orbited Saturn from 2004 to 2017, was able to spot lightning on the planet in the daytime, meaning it must have been incredibly intense — some bolts are thought to be 10,000 times more powerful than those on Earth, according to NASA. 

By observing radio emissions from the planet, Cassini was also able to 'hear' the storms discharging in the atmosphere. Saturn occasionally develops massive storms that extend more than 190,000 miles (300,000 kilometers), encircling almost the entire planet, while the gas giant's north pole plays host to a weird, permanent hexagon of clouds that extends deep into the planet.

Solar storms: Angry outbursts that knock out power grids

The sun can wreak havoc on our planet. Its solar storms consist of bursts of radiation and charged particles, which can seriously damage satellites that keep a close eye on the sun's activity and prepare for the worst, but occasionally, when a large storm heads our way, satellites and power grids need to be turned off so they can ride it out. 

Despite our best efforts, every now and again a violent solar outburst can catch us off guard. In 1859, a powerful solar flare named after astronomer Richard Carrington caused widespread interruptions to global telegraph communications. The Carrington Event of 1859 also sparked incredible aurora displays that were visible as far south as the Caribbean. 

In 1989 a solar flare ravaged the electric power transmission from the Hydro Québec generating station, causing a blackout that left six million people without electricity for nine hours. 

Solar activity has even been suggested to be a possible cause for the sinking of the Titanic. As new research suggests a solar storm behind the impressive northern light show at the time of the sinking could have disrupted the ship's navigation and communication systems and severely hindered rescue operations. 

Venus' vortex: A storm that moves faster than its planet

At the south pole of Venus is a large vortex the size of Europe swirling in the atmosphere. This vortex appears to have been around for a long time and is a result of some strange properties on the planet. The atmosphere on Venus moves faster than the planet, reaching speeds of up to 250 miles (400 kilometers) per hour — 60 times faster than the planet rotates, according to the European Space Agency. 

Venus is also the hottest planet in the solar system, but remarkably not the closest to the sun. Its hellishly dense atmosphere blankets the planet and traps heat in a runaway greenhouse effect. As a result, Venusian temperatures can reach 870 degrees Fahrenheit (465 degrees Celsius). 

Even the rain on Venus offers no relief from the heinous climate. Corrosive sulfuric acid falls from clouds and evaporates before even reaching the ground due to the extreme surface temperatures.  

Neptune's mega wind: Faster than the speed of sound

Neptune, the furthest planet from the Sun, has the fastest winds in the solar system. At the planet's highest altitudes, where methane gives Neptune its blue color, winds can reach speeds of more than 1,300 miles (2,100 kilometers) per hour or 1.6 times the speed of sound. These immense winds also give rise to some large storms, such as the famous "Great Dark Spot" seen by the Voyager 2 probe in 1989. 

Scientists are still intrigued as to the cause of this fleeting storm which had vanished by the time NASA's Hubble Space Telescope turned its gaze to Neptune some five years after Voyager 2.

Since then Hubble has kept a watchful eye on Neptune's turbulent storms which rotate clockwise due to the planet's rotation (unlike hurricanes on Earth which are low-pressure systems and rotate counterclockwise). Over the years Hubble has noted the arrival and demise of many Neptunian storms, one of which has recently perplexed scientists. 

This particular vortex had been observed sweeping southward toward Neptune's equator, following the path of various storms before it. Though unlike its predecessors this vortex made a sharp U-turn and began to drift back northwards, much to the surprise of researchers. 

Martian dust storms: Tornados visible from space

In 2018 a huge dust storm engulfed the surface of Mars, obscuring much of its surface from our view. These storms, known as "haboobs" when they occur on Earth, are fairly regular on Mars, occurring every few years, but this one was particularly large. They are caused by the sun heating the atmosphere of the planet, lifting dust off the ground — although scientists aren't sure how they grow so big, according to NASA. They pose problems for solar-powered rovers on the surface, which rely on the sun's light.

Mars also experiences dust devils — miniature tornadoes that form and move across the surface. This phenomenon is not exclusive to the Red Planet, in fact, they're also observed on Earth. 

Dust devils are formed when the ground heats up causing air close to the surface to also warm up and rise. Whilst the air rises it can come into contact with cooler small segments of air higher up which in turn cause the column of air to rotate. 

We can see these dust devils due to the dirt they kick up off the ground. They're so visible they can even be seen from space! In 2012, the Mars Reconnaissance Orbiter spotted a colossal Martian dust devil standing 2,600 feet (800 meters) tall and 98 feet (30 meters) wide. 

Titan's methane rain: You'd feel every drop

Saturn's largest moon Titan is one of the most enigmatic bodies in the solar system. This Earth-like body hosts liquid on its surface, possesses a truly bizarre climate, and has been intriguing scientists for years.

On Titan methane occasionally falls as rain, after it evaporates from the surface and forms thick clouds. Methane rain on the freezing-cold moon would fall very slowly, due to the low gravity and thick haze, so you'd feel every drop, physicist Rajani Dhingra at the University of Idaho told New Scientist in 2019.

Titan's hydrological cycle (where "hydro" relates to methane not water like on Earth), sculpts the landscape and feeds liquid methane and ethane into huge lakes such as Kraken Mare which is more than 1,000 feet (300 meters) deep. 

Astronomers have identified the most distant known object in our solar system —  a dwarf planet nicknamed Farfarout that orbits far beyond Pluto. This remote mini-planet swings so far away from the sun that from Farfarout's perspective Earth and Saturn look like neighbors. 

With an orbit that's an average of 132 times the distance between Earth and the sun, or 132 astronomical units (AU), it beats "Farout," the previous record holder for most-distant solar object; Farout orbits the sun at an average of 124 A.U. Farfarout's technical name is 2018 AG37, and it will likely get an official name as a dwarf planet down the road. 

While this space rock is big enough to take the classification "dwarf planet" and far, far out in the solar system, it's nowhere near massive enough to be Planet 9, the theoretical object astronomers were searching for when they found it. Planet 9 is believed to orbit well beyond Neptune, if it exists, and have a mass many times that of Earth's that has allowed it to stretch and warp the orbits of other outer-solar system objects with its gravity. Farfarout doesn't have the bulk to account for that stretching and warping.

Related: 5 reasons to care about asteroids

To get a sense of just how far away 132 AU is, consider the vast distance between Earth and Mars. As Live Science has reported, even during ideal conditions using a current NASA rocket the journey between the two planets would take months. But Mars orbits just 1.524 AU from the sun. Seen from Farfarout, the journey between Earth and Mars would look the same as a flight from Miami to Albuquerque would look to an observer on the moon.

Farfarout doesn't just hang out at 132 AU, however.

"A single orbit of Farfarout around the sun takes a millennium," David Tholen, an astronomer at the University of Hawaii and co-discoverer of Farfarout, said in a statement. "Because of this long orbital, it moves very slowly across the sky, requiring several years of observations to precisely determine its trajectory."

Two years of observations have revealed that Farfarout's path around the sun creates a long ellipse. At its closest, Farfarout plunges to a mere 24 AU from the sun, closer to the sun than the orbits of Pluto and Neptune. But at its farthest, it reaches deep into space, 175 AU from the sun. That's about 0.06% of the journey to the nearest star.

The researchers estimate that Farfarout is about 25 miles (400 km) wide, which would make it among the smallest of the dwarf planets. It's likely, the researchers said, that more such objects will turn up as technology for detecting dim, distant rocks improves and researchers continue hunting for the mysterious Planet Nine.

Originally published on Live Science.

Researchers are investigating an alien version of water inside the strange, icy interiors of Uranus and Neptune. 

In a new study, scientists have devised a theoretical computer model and used it to peer inside the ice giants Uranus and Neptune. With this tool, the team studied the thermal and electrical conductivity of the unusual water inside of these planets. In simulating these physical processes on the teeny-tiny atomic scale, the researchers hope that this new model will reveal information about the icy bodies' internal structure, magnetic fields, how they evolved and exactly how old they are. 

In studying Uranus and Neptune with this model, the researchers, who stem from the International School for Advanced Studies (SISSA) in Trieste, Italy and the University of California at Los Angeles, estimated that the two planets are likely primarily composed of water in some form and Uranus might even have a frozen core, according to a SISSA statement. 

Related: What is Uranus made of? 

"Hydrogen and oxygen are the most common elements in the Universe, together with helium. It is easy to deduce that water is one of the major constituents of many celestial bodies," the researchers said in the same statement. 

The team looked at three different phases of water that could exist in these planets interiors: ice, liquid and superionic (superionic water exists at extremely high temperatures and pressures.) But, as the researchers explained in the statement, water on (and inside of) an alien planet is far different from water on Earth. 

"In such exotic physical conditions, we cannot think of ice as we are used to," SISSA professors and study co-authors Federico Grasselli and Stefano Baroni said in the statement. "Even water is actually different, denser, with several molecules dissociated into positive and negative ions, thus carrying an electrical charge. Superionic water lies somewhere between the liquid and solid phases." 

So what did they find about the water inside of these ice giants? The researchers hypothesize, they explained in the statement, that Uranus might actually have a frozen core. This would explain why the planet isn't very luminous, as a frozen core would mean that very little heat would move towards the planet's surface, according to the statement. 

The scientists also found that superionic water in Uranus and Neptune is more electrically conductive than water on Earth, and they think that superionic water could compose a large portion of the dense inner layers of these gas giants. These results further our understanding of exactly how the two bodies are composed and how they came to be, the study suggests. 

As the two scientists said in the statement, "Thermal and electrical conduction dictates a "planet's history, how and when it was formed, how it cooled down. It is therefore crucial to analyze them with the appropriate tools, like the one we have developed."

This work was published July 17 in the journal Nature Communications. 

Email Chelsea Gohd at cgohd@space.com or follow her on Twitter @chelsea_gohd. Follow us on Twitter @Spacedotcom and on Facebook.

For the past few years, the possibility of a new (and big!) planet hanging around in the outermost regions of the solar system has tantalized scientists and the public alike. But after years of searching, astronomers have found zero new planets in that realm. 

Is "Planet Nine" really out there, or not?

Related: The evidence for 'Planet Nine' in our solar system (gallery)

The deep dark

We've only been studying the region of the solar system past the orbit of Neptune for a few decades now, and after a moment of introspection it's easy to see why: astronomy out here is kind of challenging, because the objects we're trying to hunt down are a) very, very small and b) very, very far away. That makes them hard to spot.

Besides Pluto, discovered by basically blind luck in 1930, our understanding of the outer solar system was completely absent until 1992, when astronomers found their first Kuiper Belt object, a frozen little remnant from the formation of the solar system, lazily circling the sun in near perfect darkness beyond Neptune.

Since then, we've found thousands more such objects, categorizing and subcategorizing them as we go (as astronomers are wont to do). For the rest of our story, we'll be focusing on a class of characters known as extreme trans-neptunian objects, or eTNOs. If you've never heard that jargon term before, don't be scared: it's astronomese for "really, really far past the orbit of Neptune."

In 2003, astronomers discovered perhaps the strangest eTNO yet, Sedna. Sedna is big, about half the size of Pluto, but sits in a truly ridiculous orbit. Over the course of 11,000 years (twice that of all of recorded human history), Sedna swings from 76 astronomical units (AU; one AU is the distance between the sun and Earth) to over 900 AU, then back again.

Sedna is weird.

The case for nine

The orbit of Sedna is so weird that it demands explanation. How can such a massive almost-planet reach such a huge, detached orbit without getting completely ejected from the solar system altogether?

Perhaps there's something else out there, keeping Sedna on a leash.

More recently, a couple teams of astronomers began to notice some other funky eTNOs. Namely, a group of half a dozen objects with similar orbits — they had roughly the same amount of ellipticity, and those ellipses were clustered together.

Imagine picking up a random flower from a field and looking at the petals. You'd normally expect the petals to be distributed evenly around the flower, but if you saw them all clustered together you might think something suspicious was going on.

And the same goes for these strange eTNOs: there was no reason to expect these kinds of orbits by random chance. The best explanation, the astronomers claimed, was that a new planet, Planet Nine (until we come up with a better name), was shaping and shepherding them in their orbits.

Related: Planet Nine likely to be found within a decade

But still eight remain

It's not a bad argument. The inability to explain the orbit of Uranus led to the detection of Neptune, so there is some historical antecedent to the strategy. And since then, more eTNOs have been found in the same strange, clustered orbits.

But in the years since the claim of a ninth planet made headlines, astronomers haven't snagged a picture of it. Which isn't too worrisome, at least not yet: if Planet Nine exists, it is very small (relatively) and very far away, making it hard to spot.

And in that same time, other astronomers have weighed in, arguing that the special eTNOs aren't so special after all. It could be that because of the way our surveys are designed and conducted, we're simply more likely to spot eTNOs with these funky orbits, and not any of their friends with more normal orbits. In other words, these eTNOs aren't shepherded by some mysterious entity in the outer solar system. There's simply nothing to explain — they only look different because we haven't finished looking yet.

What's more, it's hard to square the existence of a ninth planet with the formation of the solar system as we currently understand it. Astronomers can, of course, work to fold in a ninth planet (say, by arguing that it's an ejected failed core of a planet or a captured rogue exoplanet), but the more complicated the scenario gets, the harder it is to swallow.

Without a smoking-gun picture of the planet, the astronomical community isn't going to be fully swayed by the wayward motion of a handful of iceballs in the outer solar system. So for now the search for a new planet continues. 

• Renowned string theorist proposes new way to hunt our solar system's mysterious 'Planet 9'
• Planet Nine? 'Extreme' objects hint at more evidence of possible unseen world
• When will we find Planet Nine?

Paul M. Sutter is an astrophysicist at SUNY Stony Brook and the Flatiron Institute, host of Ask a Spaceman and Space Radio, and author of "Your Place in the Universe." Sutter contributed this article to Space.com's Expert Voices: Op-Ed & Insights. 

Learn more by listening to the episode "Does Planet Nine Exist?" on the Ask A Spaceman podcast, available on iTunes and on the Web at http://www.askaspaceman.com. Thanks to Clyde V., Scott M. Matthew A., The Manly Astronaut, Scott Monte, Michael H., and Eric C. for the questions that led to this piece! Ask your own question on Twitter using #AskASpaceman or by following Paul @PaulMattSutter and facebook.com/PaulMattSutter.

Follow us on Twitter @Spacedotcom or Facebook. 

Astronomers have discovered an unusual pattern around Neptune. The gas giant's innermost moons are doing everything in their power to steer clear from one another in a weird, zigzagging pattern that astronomers are calling a "dance of avoidance."

Thalassa and Naiad's orbital paths sit no farther apart than Chicago and Miami, about 1,150 miles (1,850 kilometers). But their zigzagging path around each other as they orbit Neptune ensures that the moons themselves never get that close. Naiad moves faster than Thalassa, circling Neptune in 7 hours versus its twin's orbital time of 7.5 hours. Every time Naiad passes the slower moon, which is when the two would otherwise veer close together, they are in a distant spot in their zigzag dance. At that point, they're about 2,200 miles (3,540 km) apart, or the distance from Chicago to Costa Rica.

Related: What Does It Take to Be a Moon?

This bizarre dance results from a resonance in the twins' orbits that keeps the moons stable as they whirl above Neptune's frigid, blue clouds.

"Resonances work both ways; they can make orbits more or less stable," study co-author Marina Brozović, a NASA Jet Propulsion Laboratory astronomer, and co-author Imke de Pater, a University of California, Berkeley, astronomer, said in a joint email to Live Science. "For the case of Naiad and Thalassa, they are more stable because the resonance maximizes the distance between the moons every time they line up."

The researchers described this bizarre orbit in a paper to be published in a forthcoming issue of the journal Icarus.

Astronomers had never seen a dance quite like this around a planet before, the researchers said, likely because the choreography relies on Naiad's unusual, sharply tilted orbit. This weird pattern had remained hidden so long because it's quite difficult to study relatively little objects around the most distant planet in our solar system.

"They are small and orbit very close to the planet, so they get lost in a bright glare of Neptune," Brozović and de Pater said. "The Hubble Space Telescope just returned a treasure trove of data that were published in February, 2019, in [the journal] Nature, so we were able to calculate the best orbits yet."

For a viewer standing on either moon, the other satellite would appear to wiggle crazily across the sky as it passed. From Thalassa's northern end, you'd seed Naiad zip overhead once before traveling over the north again on its next pass. Then, you could zoom around to the other side of the moon (if you had a superfast vehicle) and see the twin moon pass once and then twice over the south.

It's not clear how long the two little moons, much smaller than Earth's and influenced by the gravity of a much larger planet, have been locked in this pattern, the researchers said. Too much is unknown, most importantly the precise mechanics of how energy from the moons' orbits gets transfered down to Neptune. (On Earth, we see the effects of such a transfer in our tides.) But for the moment, the unusual resonance seems to protect the moons from one another, keeping them at a comfortable, stable arm's length.

• The 9 Biggest Unsolved Mysteries in Physics
• The Large Numbers That Define the Universe
• Twisted Physics: 7 Mind-Blowing Findings

Originally published on Live Science.

When Voyager 2 reached Neptune in 1989, just 12 years after setting off on its historic journey through the solar system, it discovered six new moons, took the first images of the planet's rings and noted a particularly violent storm.

The storm was something of a surprise. In the southern hemisphere there was a swirling, counter-clockwise wind of up to 1,500 mph (2,414 km/h) — the strongest ever recorded. Astronomers called it the Great Dark Spot, and while it had gone by the time the Hubble Space Telescope looked at the planet five years later, they were keen to learn why the winds were so extreme.

Related: The 12 Strangest Objects in the Universe

They were also perplexed by another issue: Voyager 2 revealed that Neptune is warmer than Uranus, despite being farther from the sun. As physicist Brian Cox discussed in his BBC documentary, The Planets: "The source of this extra heat remains a mystery." But does that mean we have a double-puzzle on our hands, and can one mystery help to explain the other in some way?

Before we begin to address the two issues at hand, we must first look at what is actually meant by "warmer." Since Neptune is a gas giant, we cannot test the globally average temperature at ground level in the way that we could on the solid surface of Earth. Instead, with Neptune's core likely to be small, temperature measurements must be taken at an altitude. Trouble is, which one?

The trouble with temperature

"We can only measure temperatures in the outermost layers," said Michael Wong, a planetary scientist at the University of California, Berkeley, via email. In doing so we find that Neptune isn't actually hotter than Uranus in real terms — they're essentially at the same temperature. But since Neptune receives less solar illumination because it's farther from the sun, this shouldn't be the case.

What this similarity in temperature suggests is that Neptune is warmer in terms of how much heat it emits in comparison to the amount of heat it absorbs from the sun. "Voyager's measurements show Neptune emits more than twice as much heat as it absorbs from the sun, while Uranus does not," Anthony Del Genio of the NASA Goddard Institute for Space Studies (GISS) told All About Space. And this is where things become rather intriguing.

That's because Neptune is not unusual in this case. "Jupiter and Saturn also emit almost twice as much heat as they absorb, but Uranus does not," Del Genio said. "Uranus is the oddball." 

Related: How Did Uranus End Up On Its Side?

"The progression of temperature as you go farther away from the sun shows Jupiter to be the warmest of the gas giants, Saturn next, then Neptune. Uranus is the one that is out of place," Del Genio said. "Yet that unusual result is associated with the fact that Uranus does not have a significant internal heat source." Neptune is finding a way to warm itself up to the level of Uranus, while the latter is unable to generate any extra heat other than that gleaned from the sun.

But just what is an internal heat source? In simple terms it is heat left over from the birth of the solar system when these planets were formed. The heat contracts out of the primitive solar nebula — an effect known as the Kelvin-Helmholtz contraction.

"The extra heat source on Neptune [and Jupiter and Saturn] is largely due to gravitational contraction," said Joshua Tollefson, also of the University of California, Berkeley. "As the planet slowly gravitationally contracts, the material falling inward changes its potential energy into thermal energy, which is then released upwards out of the planet."

Yet there is no clear reason why Uranus does not have much of an internal heat source — or any at all. "Something must have stunted this process on Uranus — perhaps due to a collision in its early history that knocked the planet on its side," said Tollefson. "The question becomes, why does Neptune have an internal heat source but Uranus does not?"

Frozen planets that love to burp

There is a possibility that heat is not released from the interior at a steady rate but instead comes in "burps". "We may just be seeing Uranus in a quiescent period, whereas Neptune has burped more recently," said Tollefson. "The burps are convection, which may happen in discrete episodes separated by long time periods, but we may not know if it works this way for sure unless we see one of these convective episodes take place."

It could also be an issue of Uranus being an old-timer and Neptune a younger pup. "How much heat a planet radiates depends mostly on how old it is and how quickly or slowly it releases that heat," said Amy Simon, a NASA senior scientist for Planetary Atmosphere Research at the NASA Goddard Space Flight Center. "An older planet would be colder. How quickly they release depends on the interior structure and composition, cloud layers, convection and so on and that can be rather complicated."

Related: 10 Interesting Places in Our Solar System We'd Like to Visit

"On the gas giants there may be significant amounts of helium rain, changing the amount of heat released. For Uranus and Neptune it is possible that they are different ages or, more likely, the event that turned Uranus onto its side may have jumbled its interior structure and/or released heat faster," said Simon.

So what of those winds? They are undeniably fierce, and this may have something to do with temperature.

"We've speculated for a long time that the coldness of Neptune and Uranus might lead to near-frictionless conditions and so allow for faster winds," said Heidi Hammel, a planetary astronomer who has studied both planets extensively and who was part of the team imaging Neptune from Voyager 2.

By this she means there are no mountains, hills or other shapes across the Neptunian landscape slowing the winds. But is there any relation between the storms and the internal heat source? "Probably," said Hammel, "but there is also some delicate balance between the internal heat and the incoming sunlight."

It is difficult to quantify these effects because of the long timescales involved. "One year on Neptune is 165 Earth years so we have not had a chance to study the planet with modern tools for very much of its seasonal cycle," said Hammel. "You need a lot of patience — and trust in past and future generations of planetary scientists — to study the atmospheres of outer planets."

"I guess the theory was supposed to be the greater amount of solar energy, the more wind energy, but on Earth we've known for a long time that the amount of energy received by the sun and converted into kinetic energy in the atmosphere — that is, wind — is a tiny fraction,” said Del Genio.

Earth is a very inefficient heat engine, and it doesn't give you much bang for the buck. One reason is that it has a solid surface that dissipates wind energy by friction, whereas the gas giants do not, so that is one reason why all the giant planets have much stronger winds than Earth does.

Why are Neptune's winds so strong?

"Winds are probably generated deeper than sunlight can penetrate, so a combination of internal heat and rotation likely produces them," said Simon, raising the issue of why Uranus and Neptune's winds don't match, given they have similar rotation rates. "It tells us something is different between them: partially internal heat or something else," said Simon.

Uranus' winds can blow up to 560 mph and Neptune's 1,500 mph. "They're both extremely fast and peak at speeds faster than Jupiter," said Tollefson. NASA says Jupiter's Great Red Spot can blow at 384 mph. But he too says internal heat alone cannot explain the speeds, given Uranus does not generate extra heat.

The interior structure of the planets — their masses, core sizes and radial density profiles — is extremely important for understanding the winds as we see them. How the winds form and how deep they go are questions currently being answered for Jupiter and Saturn thanks to NASA's Juno and Cassini spacecraft. This is due to the extremely good gravitational data they've obtained, which means good models for the interior structure can be made.

Related: Jupiter's Great Red Spot: Our Solar System's Most Famous Storm

Computer simulations suggest that the winds of the ice giants are confined to shallow depths in the upper layers of their atmospheres. This may suggest that the fast winds we see on Uranus and Neptune are at least partly due to the latent heat release of condensation for materials like water.

Del Genio also questions the available data. He explains that when we measure winds on Neptune, we look at one specific altitude. "The winds at other altitudes may be slower or faster," said Del Genio. "We don't know because we have never dropped probes into the atmospheres of most of the outer planets."

What Neptune and Uranus show is that planets which form in similar conditions can provide two extremes. Simon says this helps us constrain models of how these planets form and give clues about the solar system's overall formation. "They should also help us better understand deeper circulation, given they are so far from the sun."

"It adds to our knowledge of the physics and chemistry in planetary atmospheres and helps us understand our own Earth a little better, since the physics and chemistry operate in the same way whether here on Earth or on distant Neptune," said Hammel.

Additional resources:

• The Greatest Mysteries of Neptune
• 11 Fascinating Facts About Our Milky Way Galaxy
• The 9 Most Intriguing Earth-Like Exoplanets

Solar system marvels

Yellowstone National Park may have stunning vistas that impress mere Earthlings, but they’re nothing compared to strange and fascinating locations elsewhere in our solar system. Jupiter's Great Red Spot is a colossal storm larger than Earth. Venus' surface temperature is hot enough to melt lead. The largest mountain on any planet in our solar system, Mars' Olympus Mons, is three times higher than Mount Everest. And while any space geek worth her Europan sea salt might know about these splendors, the marvels of the solar system are almost endless. Here, we take a look at some of the less-well-known spots in our cosmic neighborhood that we’d most like to visit.

Mercury's ice traps

Up close to the blazing sun is not a place most people would think to look for frozen ice. But as the little planet Mercury spins next to its fiery parent star, a few craters at the poles are permanently hidden deep in shadow. With an ambient temperature of minus 280 degrees Fahrenheit (minus 173 degrees Celsius), these "deep-freeze traps" are the perfect place for water ice to accumulate over the eons. All together, these ice traps could hold more water than similar deposits on the moon, Sean Solomon, director of the department of terrestrial magnetism at the Carnegie Institution of Washington, previously told Live Science.

Venus: Abode of life?

Bone-dry and hellishly hot, Venus seems unlikely to contain an oasis. Yet 30 miles (48 kilometers) above its infernal surface, there exists a cloud layer with downright balmy conditions. Temperatures and pressures here are not all that different from those found on the Earth's surface. The ample sunshine and complex chemicals could provide power to photo- and chemosynthetic organisms. The only downside? There's a fair amount of sulfuric acid in the clouds. But then again, extremophile microbes on Earth have endured much harsher environments.

Comet-Asteroid Phaethon

The space rock Phaethon sports a rare blue color and an extremely eccentric orbit that takes it close to the sun and then past Mars. Such an orbit is typical of icy comets, but when Phaethon approaches our solar system's central star, it doesn't produce the beautiful tail-like coma characteristic of nearly all comets.Therefore, many astronomers consider it to be more like an asteroid. Theories abound about what exactly is going on with this odd object, including the possibility that it is a dormant comet, or a comet that turned into an asteroid over time.

Ida and Dactyl

In 1993, the Galileo spacecraft was en route to Jupiter. Along the way, it stopped to photograph an unusual object—the asteroid Ida, which became only the second asteroid ever to be visited by a probe. Ida contained a tiny surprise for scientists: an itty-bitty moon named Dactyl, the first satellite discovered orbiting around an asteroid. Both objects are a bit strange in that they experience space-weathering from the sun that causes their surfaces to turn red over time. Scientists are still scratching their heads over exactly how old Ida is and how it got this little moon.

Janus and Epimetheus

The ringed beauty Saturn is host to a wide variety of wonderful moons. And two of its potato-shaped satellites, Janus and Empimetheus, have in a unique arrangement. These special partners share an orbit wherein one is 31 miles (50 km) closer to Saturn than the other is. Once about every four years, the more distant moon catches up to the closer one, and the two perform a gravitational do-si-do, switching places. No other moons in the solar system are known to have such interchanging orbital mechanics.

Yin-Yang Iapetus

Saturn's third-largest moon, Iapetus, is a walnut-shaped wonder, with a bulging equator and a bizarre black-and-white surface. One hemisphere of the satellite is coal-black, while its other side is far brighter. A raised mountain range encircles its equator, containing some of the highest peaks in the solar system. So far, no one has been able to explain Iapetus' two-tone appearance; some astronomers suggest that the murkier side could have been created by particles originating from another of Saturn’s moons, Phoebe, or perhaps by the eruption of dark hydrocarbons from ice volcanoes. There have even been conspiracy-like whispers that Iapetus is not a natural satellite, but rather something built or modified by an alien civilization, though that possibility is well outside mainstream scientific thinking.

Miranda's Gnarly Cliffs

The ice giant Uranus' moon Miranda is a spelunkers dream — its jagged surface is replete with canyons, scarps, terraced outcrops, and a cliff whose floor is approximately 12.4 miles (20 km) down, the highest known cliff in the solar system. Miranda's geological scars could be due to flowing ice from the moon's interior that, at some point, were pushed up to the surface. An even wilder theory proposes that the moon was shattered several times and came back together, creating its extremely uneven features.

Triton and Proteus

Triton is the largest of blue Neptune's moons, and the only round one.This moon is high on the list of researchers' places to send a spacecraft, because it sports so many strange qualities. Triton is on a "retrograde" orbit, revolving in the opposite direction of the planet and other moons, suggesting it could have been a captured, Pluto-like body. From its surface rise bizarre ice volcanoes, making it one of the farthest bodies in the solar system known to have active geophysics. Triton's sibling, Neptune’s second largest moon, Proteus, is also pretty unusual. Rather than being round, this moon is shaped like what mathematicians call an irregular "polyhedron" (a solid object with many plane faces), and what "Dungeons and Dragons" nerds know as a 20-sided dice. Proteus' surface is pinkish-red, perhaps the result of complex organic compounds like hydrocarbons.

Ultima Thule

After speeding by distant Pluto, NASA's New Horizons mission made a brief encounter with an even more out-there body. Nicknamed Ultima Thule, the frozen Kuiper belt object at first looked like two spheres stuck together, forming a celestial snowman. But after the spacecraft completed its flyby, Ultima Thule was revealed to be as flat as a pancake, more like two skipping stones that had somehow gotten wedged to one another. Scientists are likely to ponder this strange state of affairs for a long time.

The Sun's Tail

At the edge of the solar system, where the sun's influence is nearly depleted, lives a large structure called the heliotail. The tail drags behind the bullet-shaped heliosphere, a bubble surrounding our solar system that was created by the sun's wind and magnetic field. The comet-like heliotail had never been seen until NASA's Interstellar Boundary Explorer (IBEX) photographed it in 2013, finding what looked unexpectedly like a four-leaf clover. This quadratic shape arises from the fast solar wind shooting out from near the sun's poles and slower wind flowing from near the sun's equator, researchers told Live Science's sister site, Space.com.

A faint and frigid little moon doesn't have to go by "Neptune XIV" anymore.

Astronomers have given a name — "Hippocamp" — to the most recently discovered moon of Neptune, which also formerly went by S/2004 N1. They've figured out how big the satellite is as well, and teased out some interesting details about its past, a new study reports.

A team led by Mark Showalter, of the SETI (Search for Extraterrestrial Intelligence) Institute in Mountain View, California, announced the existence of S/2004 N1 in 2013. The scientists did so after analyzing photos taken by NASA's Hubble Space Telescope between 2004 and 2009. [See Photos of Neptune, The Mysterious Blue Planet]

Back then, the team determined that S/2004 N1 lies about 65,400 miles (105,250 kilometers) from its parent planet and completes one orbit every 23 hours or so. For comparison, Earth's own moon — at 2,160 miles wide (3,475 km) a giant compared with the Neptune satellite — orbits our planet at an average distance of about 239,000 miles (384,600 km). 

And the researchers pegged S/2004 N1 as the smallest of Neptune's 14 known moons, estimating its diameter to be no greater than 12 miles (19 km). 

But things have changed a bit since then, as the new study — also led by Showalter — reports. The team has updated its assessment of the moon, after incorporating new Hubble observations made in 2016.

But let's talk about the new name first. "Hippocamp" is a horse-headed, fish-tailed creature in Greek mythology. The moniker, which has been approved by the International Astronomical Union, is in keeping with naming conventions for the Neptune system, which demand an association with Greco-Roman mythology and the sea. (Neptune, of course, is the Roman god of the sea, the equivalent of the Greek Poseidon.)

But Hippocampus is also the genus name for real-life seahorses. And Showalter is a scuba diver who loves these beautiful and bizarre little creatures.

"So, officially, it's named after this mythological creature," Showalter told Space.com. "But partly, in my mind, it's named after seahorses, because I think they're cool."

In the new Hippocamp analysis, which was published today (Feb. 20) in the journal Nature, Showalter and his team employed a clever technique they devised a few years back (which allowed them to discover the moon in the first place). The scientists "transformed" eight sequential 5-minute Hubble exposures of the Neptune system, rearranging pixels so they could "stack" images of Hippocamp on top of each other despite the moon's orbital motion. 

Essentially, the researchers turned the eight individual exposures into a single 40-minute exposure.  

"We came really close to missing it entirely," Showalter said of Hippocamp. "It's too faint to see in a single Hubble [exposure]." [The Moons of Neptune Unmasked! (Infographic)]

This technique is powerful; applying it broadly "might result in the detection of other small moons around giant planets, or even planets that orbit distant stars," astronomer Anne Verbiscer of the University of Virginia, who was not part of Showalter's team, wrote in an accompanying "News and Views" piece in the same issue of Nature.

The new analysis describes a slightly larger world than previously thought: Hippocamp is now believed to have a diameter of about 21 miles (34 km), the researchers report. That's about the same size as Ultima Thule, the weird and distant object that NASA's New Horizons spacecraft flew by on New Year's Day. 

Hippocamp circles in the same general neighborhood as six moons discovered by NASA's Voyager 2 spacecraft during the probe's flyby of Neptune in 1989. Hippocamp is just 7,450 miles (12,000 km) interior to the largest and outermost of these other six, the 260-mile-wide (420 km) Proteus.

Like Earth's own moon, Proteus has been slowly spiraling away from its parent planet for eons — and so has Hippocamp, though at a much slower rate. About 4 billion years ago, Proteus was probably right next to Hippocamp and would therefore have gobbled the smaller moon up, Showalter said.

So, he and his colleagues suspect that Hippocamp is younger than Proteus. In fact, they believe the smaller moon was once part of its larger neighbor: Hippocamp likely coalesced from pieces of Proteus that were blasted into space by a long-ago comet impact, the researchers wrote in the new Nature paper.

Indeed, Hippocamp may trace its origin to the smashup that created Proteus' huge Pharos Crater. Hippocamp's total volume is about 2 percent of that ejected during the Pharos impact. It's not hard to imagine this small amount of material coalescing to form a moon, Showalter said.

In the 1980s and '90s, astronomers began to posit that the moons of the giant planets endured a number of comet collisions, which caused many of the satellites to break apart. The inferred origin of Hippocamp supports this view of the early solar system, said Showalter, who has played a key role in the discovery of many natural satellites over the years, including Saturn's "ravioli moon" Pan in the early 1990s.

"This is the first really great example of a moon that got created as a result of an impact," he said.

Showalter and his team also used the transformation-stacking technique to spot the Neptune moon Naiad, which hadn't been seen since its discovery by Voyager 2 in 1989. And the researchers set some limits on the possibility of finding other moons of the ice giant: Their analyses suggest there are no moons wider than 15 miles (24 km) interior to Proteus, and none at least 12.4 miles (20 km) wide beyond that same satellite, Verbiscer noted.

Mike Wall's book about the search for alien life, "Out There " (Grand Central Publishing, 2018; illustrated byKarl Tate is out now. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook. 

The weirdly clustered orbits of some far-flung bodies in our solar system can be explained without invoking a big, undiscovered "Planet Nine," a new study suggests. 

The shepherding gravitational pull could come from many fellow trans-Neptunian objects (TNOs) rather than a single massive world, according to the research.

"If you remove Planet Nine from the model, and instead allow for lots of small objects scattered across a wide area, collective attractions between those objects could just as easily account for the eccentric orbits we see in some TNOs," study lead author Antranik Sefilian, a doctoral student in the Department of Applied Mathematics and Theoretical Physics at Cambridge University in England, said in a statement. [The Evidence for 'Planet Nine' in Our Solar System (Gallery)]

The hunt for Planet Nine — or, as some prefer to call it, Planet X or Giant Planet Five — began in earnest in 2014. That year, astronomers Chad Trujillo and Scott Sheppard proposed the existence of a large, unseen "perturber" beyond Neptune, whose gravitational influence could explain oddities in the orbits of distant objects like the dwarf planets Sedna and 2012 VP113.

In January 2016, Konstantin Batygin and Mike Brown contributed more evidence, announcing that other TNOs also appeared to bear this gravitational imprint. Batygin and Brown estimated that the perturber is perhaps 10 times more massive than Earth and lies about 600 astronomical units (AU) from the sun on average. (One AU is the Earth-sun distance — about 93 million miles, or 150 million kilometers.)

The case has been building ever since, as astronomers have found more and more "clustered" TNOs; the tally is up to about 30 at the moment. 

But Planet Nine's existence isn't a slam dunk: Some astronomers think the orbit-shaping tug is more likely coming from many small bodies. The new study, which Sefilian conducted with Jihad Touma of the American University of Beirut, explores this latter scenario.

The duo's modeling work suggests that the strength-in-numbers explanation does indeed work — if the mass of the Kuiper Belt, the ring of bodies beyond Neptune, is a few to 10 times that of Earth. This is a pretty big "if," given that most estimates peg the Kuiper Belt's mass at less than 10 percent that of Earth (and one recent study put the figure at 0.02 Earth masses).

But other solar systems are known to harbor massive disks of material in their outer reaches, Sefilian and Touma noted. And our failure to spot one around our own sun doesn't mean it doesn't exist, they stressed.

"The problem is, when you're observing the disk from inside the system, it's almost impossible to see the whole thing at once. While we don't have direct observational evidence for the disk, neither do we have it for Planet Nine, which is why we're investigating other possibilities," Sefilian said.

"It's also possible that both things could be true — there could be a massive disk and a ninth planet," he added. "With the discovery of each new TNO, we gather more evidence that might help explain their behavior."

The new study has been accepted for publication in the Astronomical Journal. You can read it for free at the online preprint site arXiv.org.

Mike Wall's book about the search for alien life, "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate) is out now. Follow him on Twitter @michaeldwall. Follow us @Spacedotcom or Facebook. Originally published on Space.com. 

The Rosetta space probe's "rubber ducky" comet seems likely to have emerged from a gentle kiss in the cold black of outer space. And the comet might have a secret to tell about Neptune.

Comet 67P, where the European Space Agency (ESA) landed its Rosetta probe back in the summer of 2016, has a strange shape. It is fairly small, just about 2.5 miles (4.1 kilometers) at its widest point, and consists of two bulging lobes linked together by a narrow neck. In an unpublished paper awaiting peer review that appeared in the preprint journal arXiv, astronomers detailed how the comet may have formed and migrated into the orbit of Jupiter. And that history has important implications for the early history of the solar system, particularly for the planet Neptune, the researchers said. [Danger! Falling Rocks: Meteorites and Asteroids (Infographic)]

Astronomers don't have time machines; they can't travel to the past and see how 67P formed. But they can use the information they do have about the comet and our solar system to model the object's history. And that model has led to some fascinating conclusions about what the solar system looked like eons ago, when 67P likely formed.

The solar system is a roiling field of orbiting objects, tugging on one another with gravity. So, there are limits to how precisely astronomers can track 67P backward through time. Researchers already knew that the comet passed near Jupiter on Feb. 4, 1959, and Oct. 2, 1923. Peering further into the past, though, is much more difficult, the scientists said.

But by modeling dozens of paths that could have pointed the comet to its current position, the researchers concluded that the object likely moved into the inner solar system more than 1,000 years ago. That was after it formed and spent eons orbiting the sun 20 to 30 times farther away than planet Earth is located, in a giant cloud of rubble. 

But that trajectory poses a problem, because unless 67P broke off from a larger comet, it almost certainly wouldn't have survived the version of the early solar system that scientists have long imagined, the researchers in the new study said.

Most histories of the early solar system have a disk of dust and rubble orbiting at 20 to 30 times Earth's current distance from the sun. In this cloud of material, billions of years ago, little clumps of dirt formed and banged into one another, sometimes clumping together into larger objects and sometimes falling apart.

In the most common version of this story, that cloud lasted about 400 million years. But the astronomers in the new study found that if that were true, 67P almost certainly wouldn't have survived. Over all that time, the comet would have smashed into other objects and fallen apart, the researchers said.

So 67P's survival lends credence to another hypothesis: Perhaps Neptune, which once orbited much closer to the sun, drifted out through that disk of matter soon after the disk formed 4.5 billion years ago. Neptune's drifting could have caused the disk to disperse, saving 67P from collisions in the rough and tumble environment of the rubble disk that spawned the comet, the new study said.

If Neptune's bulk absorbed or dispersed most of the rubble just 10 million years after the disk formed, that might explain how 67P survived to the present, the study said. Four-hundred million years? Deadly. But 10 million? That's a short enough span of time spent in the dirt cloud for 67P to have survived intact, the researchers wrote in their study.

Cosmic kiss

The astronomers didn't offer a firm answer on how 67P itself was formed. It's possible, they wrote, that a mound of rubble just formed in its current, rubber-ducky shape from the beginning, though there are reasons to doubt that hypothesis.

 The two lobes could also have resulted from two smaller comets orbiting one another, called a binary, coming together, and there are two possibilities for how that might have happened, the study said. Maybe a slowly orbiting binary brushed past a planet and got nudged into forming a single comet. Or maybe tiny collisions with other rocks pushed the two lobes together until they met.

A brush with a planet pushing the binary together, the researchers found, is unlikely. Such a close encounter with a planet would likely destroy most comets.

But maybe, out in that rubble cloud, pebbles bashed into the two orbiting chunks of 67P over and over. Each of those collisions would have sapped a bit of energy from the binary orbit, slowing the orbiting chunks down, the study said.

The pieces would have already been moving pretty slowly, the authors wrote. The lightweight lobes of 67P would have orbited one another at just a few feet per second back then. As the chunks experienced collisions, that speed would have dropped over time, until the pieces came together relatively gently.

It seems very likely, then, that Rosetta's comet formed in this billions-of-years-old kiss, the two lobes locking together and drifting a long way through space before arriving in a spot where humans could reach out and touch them.

Originally published on Live Science.

It's both solid and liquid, it's 60 times denser than ordinary water ice, and it forms at temperatures almost as hot as the sun's surface.

It's superionic ice — and for the first time, scientists have made it in the lab.

This high-pressure form of water ice has long been thought to exist in the interiors of Uranus and Neptune. But until now, its existence was only theoretical.

"Our work provides experimental evidence for superionic ice and shows that these predictions were not due to artifacts in the simulations, but actually captured the extraordinary behavior of water at those conditions," Marius Millot, a physicist at Lawrence Livermore National Laboratory in California, said in a statement from the laboratory. Millot was the leader author of a new study describing the work.

Scientists first predicted the existence of a weird water phase that makes the substance both solid and liquid at the same time 30 years ago. It's also way denser than ordinary water ice because it forms only under extreme heat and pressure, such as those found inside giant planets. During the superionic phase, the hydrogen and oxygen within water molecules behave bizarrely; hydrogen ions move like a liquid, inside of a solid crystal lattice of oxygen. [The Surprisingly Strange Physics of Water]

Making the ice was complicated. First, the team compressed water into an ultrastrong cubic crystalline ice, in a different crystal form than what you see in ordinary ice cubes. To do that, the researchers used diamond anvil cells to apply 360,000 pounds per square inch (2.5 gigapascals (GPa) of pressure; that's about 25,000 times the atmospheric pressure on Earth). Next, the researchers heated and compressed the cells even further, using laser-driven shocks. Each crystal ice structure received up to six laser beams of more than 100 times that high pressure.

"Because we pre-compressed the water, there is less shock-heating than if we shock-compressed ambient liquid water," Millot said. The new method lets researchers "access much colder states at high pressure than in previous shock-compression studies."

Once the superionic ice was ready, the team moved quickly to analyze its optical and thermodynamic properties. They had only 10 to 20 nanoseconds to perform the work, before pressure waves released the compression, and the water dissolved. And the results were bizarre. They found that the ice melts at an extraordinary 8,540 degrees Fahrenheit (4,725 degrees Celsius ) at 29 million pounds per square inch (200 GPa) of pressure. That pressure is about 2 million times the atmospheric pressure on Earth.

"It's … mind-boggling that frozen water ice is present at thousands of degrees inside these planets, but that's what the experiments show," Raymond Jeanloz, a co-author of the study and planetary physicist at the University of California, Berkeley, said in the same statement.

The new findings could provide a peek inside the interiors of planets such as Uranus and Neptune. Planetary scientists suggest these worlds' innards are composed of up to 65 percent water by mass, plus some ammonia and methane.

Previous work suggested these planets would have "fully fluid" heat-transferring interiors, but the addition of superionic ice changes the picture. The new research instead proposes "a relatively thin layer of fluid and a large 'mantle' of superionic ice," the researchers said in the statement.

That picture of the mini-giant planets' interiors would confirm a computer simulation performed a decade ago that tried to explain the weird magnetic fields at Uranus and Neptune. Uranus' magnetic field is tilted 59 degrees away from the planet's axis. Neptune's magnetic poles have a roughly 47-degree tilt. This is extreme compared with Earth, which has only an 11-degree tilt. Their magnetic fields also may behave differently; for example, Uranus' field may turn on and off like a strobe.

More detailed study of these planets will have to wait until a spacecraft is available. Fortunately, NASA is proposing a Uranus and/or Neptune spacecraft that would zoom out to these planets sometime in the next few decades. Meanwhile, the experimenters plan to push their compression further to simulate conditions inside of even larger giant planets, such as Jupiter or Saturn.

A study based on the research was published in February in the journal Nature Physics.

Original article on Live Science.

Planet Nine is out there, and astronomers are determined to find it, according to a new statement from NASA. In fact, mounting evidence suggests it's hard to imagine our solar system without the unseen world. 

The hypothetical planet is believed to be about 10 times more massive than Earth and located in the dark, outer reaches of the solar system, approximately 20 times farther from the sun than Neptune is. While the mysterious world still has yet to be found, astronomers have discovered a number of strange features of our solar system that are best explained by the presence of a ninth planet, according to the NASA statement. 

"There are now five different lines of observational evidence pointing to the existence of Planet Nine," Konstantin Batygin, a planetary astrophysicist at the California Institute of Technology (Caltech) in Pasadena, said in the statement. "If you were to remove this explanation and imagine Planet Nine does not exist, then you generate more problems than you solve. All of a sudden, you have five different puzzles, and you must come up with five different theories to explain them." [The Evidence for 'Planet Nine' in Our Solar System (Gallery)]

In 2016, Batygin and co-author Mike Brown, an astronomer at Caltech, published a study that examined the elliptical orbits of six known objects in the Kuiper Belt, a distant region of icy bodies stretching from Neptune outward toward interstellar space. Their findings revealed that all of those Kuiper Belt objects have elliptical orbits that point in the same direction and are tilted about 30 degrees "downward" compared to the plane in which the eight official planets circle the sun, according to the statement. 

Using computer simulations of the solar system with a Planet Nine, Batygin and Brown also showed that there should be even more objects tilted a whopping 90 degrees with respect to the solar plane. Further investigation revealed that five such objects were already known to fit these parameters, the researchers said. 

Since then, the astronomers have found new evidence that further supports the existence of Planet Nine. With help from Elizabeth Bailey, an astrophysicist and planetary scientist at Caltech, the team showed that Planet Nine's influence might have tilted the planets of our solar system, which would explain why the zone in which the eight major planets orbit the sun is tilted by about 6 degrees compared to the sun's equator.

"Over long periods of time, Planet Nine will make the entire solar-system plane precess, or wobble, just like a top on a table," Batygin said in the statement. 

Finally, the researchers demonstrate how Planet Nine's presence could explain why Kuiper Belt objects orbit in the opposite direction from everything else in the solar system. 

"No other model can explain the weirdness of these high-inclination orbits," Batygin said in the statement. "It turns out that Planet Nine provides a natural avenue for their generation. These things have been twisted out of the solar system plane with help from Planet Nine and then scattered inward by Neptune."

Going forward, the researchers plan to use the Subaru Telescope at Mauna Kea Observatory in Hawaii to find Planet Nine, and then deduce where the mysterious world came from. 

The most common type of planets discovered around other stars in our galaxy has been what astronomers call "super Earths" — rocky worlds that are larger than Earth but smaller than Neptune. However, no such planet has yet been discovered in our solar system, meaning that Planet Nine could be our missing "super Earth," the researchers said. 

Follow Samantha Mathewson @Sam_Ashley13. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.

For the first time, the kind of diamond rain that scientists think falls within the icy giant planets of the solar system has been generated in the lab, a new study finds.

Thousands of miles below the surfaces of icy giant planets such as Neptune and Uranus, carbon and hydrogen are thought to compress under extreme heat and pressure to form diamonds, according to previous research going back 30 years. These diamonds are then thought to sink through the layers of the gas giant planets, creating a "diamond rain" that eventually settles around the planetary cores.

However, until now, scientists could not confirm whether, when and how such diamond rain could actually form in the chemistry, temperatures and pressures found deep within ice giants. [Our Solar System: A Photo Tour of the Planets]

Researchers simulated the interior of ice giants by creating shock waves in polystyrene (a kind of plastic) with an intense laser at SLAC National Accelerator Laboratory in Menlo Park, California. The polystyrene simulated molecules known as hydrocarbons that are derived from methane, the compound that gives Neptune its blue tint. These hydrocarbons are what diamonds are thought to form from in the high pressures and temperatures in the intermediate layers of ice giants.

The scientists used the laser to generate pairs of shock waves, with the first member of each pair overtaken by its stronger partner. When the shock waves overlapped, diamonds formed at temperatures of about 8,540 degrees Fahrenheit (4,725 degrees Celsius) and pressures about 1.48 million times greater than Earth's atmospheric pressure at sea level. Such conditions resemble the environments about 6,200 miles (10,000 kilometers) below the surfaces of Neptune and Uranus, the researchers said.

"It was very surprising that we got such a clear diamond signature and that the diamonds formed so quickly," said study lead author Dominik Kraus, an experimental laser-plasma physicist at the Helmholtz-Zentrum Dresden-Rossendorf research laboratory in Germany, told Space.com. "I was expecting to look for very tiny hints in the data, and our theorist co-workers actually predicted that it might be impossible to observe diamond formation in our experiment. I already prepared my team for a very difficult experiment and data analysis. But then, the data was just incredibly clear from the first moments in the experiment."

As the diamonds were born, the scientists analyzed them using intense, fast pulses of X-rays only 50 femtoseconds long — essentially, the "shutter speed" of this laser camera is 50 millionths of a billionth of a second, and can thus capture very-fast-moving chemical reactions. These X-ray snapshots helped capture the exact chemical composition and molecular structures of the diamonds as they formed.

In the experiments, the researchers saw that nearly every carbon atom of the plastic targets got incorporated into diamonds up to a few nanometers (billionths of a meter) wide. They predicted that if similar reactions happened within Neptune and Uranus, diamonds could become much larger, perhaps millions of carats large. (One carat is 200 milligrams, or 0.007 ounces.)

But don't expect these findings to generate a rush of diamond miners to Neptune or Uranus. 

"The diamonds created in ice giants and our experiment are certainly not gem-quality cut and polished brilliants," Kraus told Space.com. Instead, they are probably spherical diamonds loaded with impurities, he said.

The researchers suggested that over thousands of years, these diamonds would slowly sink through the icy layers within ice giants, assembling into a thick layer around the cores of these planets.

"Some models predict that the temperature around the core may be high enough that diamond would melt, forming underground seas of liquid metallic carbon, maybe with some diamond 'icebergs' swimming on top," Kraus said. "This could help to explain the unusual magnetic fields of Uranus and Neptune. However, most models suggest that diamond would remain solid around the cores of Neptune and Uranus."

As these diamonds rain downward, they are expected to generate heat, much as meteors burn as they plummet through Earth's atmosphere. This heat could help explain why Neptune is hotter than expected, Kraus said.

Moreover, these new findings could help shed light on the inner workings of distant planets outside the solar system and, in turn, help researchers better model and classify such exoplanets, Kraus said.

The researchers added that one day, the microscopic "nanodiamonds" they created could be harvested for commercial purposes, such as medicine and electronics. Currently, nanodiamonds are commercially produced using explosives, and "high-energy lasers may be able to provide a more elegant and controllable method," Kraus said. However, the lasers they use currently accelerate the diamonds they create to very high speeds of about 11,185 mph (18,000 km/h), "and we need to gently stop them," he said.

Furthermore, these findings could help researchers understand and improve experiments that seek to generate energy from nuclear fusion. In some of these experiments, hydrogen fuel is surrounded by a layer of plastic and is then blasted with lasers, and these new findings suggest "that considering chemical processes may be important for modeling some types of fusion implosions," Kraus said.

Future research can investigate the roles that other elements — such as oxygen, nitrogen and helium — might play in ice giants, Kraus said. He and his colleagues detailed their findings online Aug. 21 in the journal Nature Astronomy.

Follow Charles Q. Choi on Twitter @cqchoi. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.

As Earthlings, we have the privilege of ooohing and aaahing at total solar eclipses, those dazzling celestial events in which the moon blocks the sun's light from hitting our planet. But is Earth the only world in our solar system that experiences this spectacular phenomenon?

The answer is no. Total solar eclipses can happen on other planets too, as long as they have moons that are big enough to cover the sun's disk from the planet's perspective and orbit the planet on the same plane as the sun, astronomers told Live Science.

A total solar eclipse occurs when a planet, its moon and the sun are aligned along the same plane, and a substantially sized moon passes between the planet and its sun, totally blocking the sun's light from reaching the planet.

"To get a solar eclipse, the first thing you need is a moon," said Christa Van Laerhoven, a postdoctoral fellow of astronomy at the University of British Columbia in Canada. "This immediately rules out solar eclipses on Mercury or Venus" — two planets without moons, she said. [What Would Earth Be Like with Two Suns?]

Mars has two moons — Phobos and Deimos — but both are too small to create total solar eclipses that would be visible from the Red Planet. Rather, these moons can make partial eclipses for any potential life-form (or Mars rover) watching from the ground, Van Laerhoven said.

"The view from those little moons is more interesting: They see Mars eclipsing the sun very frequently, and during some seasons, it happens every day," astronomer Matija Cuk wrote on the Cornell University blog "Ask an Astronomer."

The gas giants — Jupiter, Saturn, Uranus and Neptune — can all have total solar eclipses, as they have large moons and the sun appears small to them, Cuk said. But because these planets are made of gas, it would be impossible to stand on them and see such solar eclipses, he said.

However, if you had a special spaceship that could hover near the swirling gas giants, you could very well glimpse a solar eclipse. Jupiter has up to 67 moons, including Ganymede, the largest moon in the solar system. Because Jupiter's moons orbit on the same plane as the sun, the planet can have solar eclipses, Cuk and Van Laerhoven said.

In fact, if you could land on one of Jupiter's moons, you could see its other moons eclipse the sun, the astronomers said.

But what about dwarf planets, such as Pluto? "Charon [Pluto's largest moon] is large enough and close enough to Pluto to produce total solar eclipses for Pluto," Van Laerhoven said. But because the same side of Pluto and Charon always face each other, "only one side of both Pluto and Charon will ever experience eclipses," Cuk wrote.

On Earth, the moon is almost perfectly suited to making eclipses. The moon is the right size — that is, it appears to be the same size or larger than the apparent size of the sun, as seen from Earth. "This means that when the moon passes in front of the sun, the photosphere [the sun's luminous outer shell] gets covered, but the corona [the sun's upper atmosphere] remains visible," Van Laerhoven said. [Why Total Solar Eclipses Are Total Coincidences]

She noted that Earth's moon is slowly moving farther away from our planet, so in the distant future, the moon's apparent size will be too small to entirely cover the sun, at least from Earth's perspective. This means that one day, the moon won't be able to cause total solar eclipses but only annular eclipses, in which a "ring" of the sun's disk is still visible, Van Laerhoven said. Experts speculate that Earth will experience its last total solar eclipse about 600 million years from now.

For now, however, the moon is in prime location to cause a total solar eclipse.

"The reason we don't get solar eclipses every month is because the moon's orbital plane is slightly misaligned from Earth's orbital plane around the sun," Van Laerhoven said. "If they are misaligned, that decreases your chances of having a solar eclipse. You only get it when things happen to be lined up."

REMEMBER: Looking directly at the sun, even when it is partially covered by the moon, can cause serious eye damage or blindness. NEVER look at a partial solar eclipse without proper eye protection. Our sister site Space.com has a complete guide for how to view an eclipse safely.

Original article on Live Science.

Pluto isn't quite as lonely as scientists had thought.

Astronomers have discovered another dwarf planet in the Kuiper Belt, the ring of icy objects beyond Neptune. But this newfound world, dubbed 2015 RR245, is much more distant than Pluto, orbiting the sun once every 700 Earth years, scientists said. (Pluto completes one lap around the sun every 248 Earth years.) You can see an animation of the new dwarf planet's orbit here.

"The icy worlds beyond Neptune trace how the giant planets formed and then moved out from the sun," discovery team member Michele Bannister, of the University of Victoria in British Columbia, said in a statement. "They let us piece together the history of our solar system." [Meet the Solar System's Dwarf Planets]

"But almost all of these icy worlds are painfully small and faint; it's really exciting to find one that's large and bright enough that we can study it in detail," Bannister added.

The exact size of 2015 RR245 is not yet known, but the researchers think it's about 435 miles (700 kilometers) wide. Pluto is the largest resident of the Kuiper Belt, with a diameter of 1,474 miles (2,371 km).

The research team first spotted 2015 RR245 in February of this year, while poring over images that the Canada-France-Hawaii Telescope in Hawaii took in September 2015 as part of the ongoing Outer Solar System Origins Survey (OSSOS).

"There it was on the screen — this dot of light moving so slowly that it had to be at least twice as far as Neptune from the sun," Bannister said.

OSSOS has discovered more than 500 objects beyond Neptune's orbit, but 2015 RR245 is the first dwarf planet that the survey has found, the scientists said.

Dwarf planets are massive enough to be crushed into spheres by their own gravity, but they have not "cleared their neighborhood" of other objects, which differentiates them from "normal" planets such as Earth and Saturn. This definition, which was devised by the International Astronomical Union in 2006, led to Pluto's controversial reclassification as a dwarf planet.

Astronomers are still working out the details of 2015 RR245's highly elliptical orbit, but the object appears to come as close to the sun as 34 astronomical units (AU), and farther away than 120 AU. (One AU is the average Earth-sun distance — about 93 million miles, or 150 million km.)

2015 RR245 — which will get a catchier, official name at some point — will make its closest approach to the sun in 2096, the researchers said.

Other confirmed dwarf planets in the Kuiper Belt region include Pluto, Eris, Haumea and Makemake. Several other objects in this distant realm, including Sedna, Quaoar and 2007 OR10, probably meet the dwarf-planet criteria as well, scientists have said.

Follow Mike Wall on Twitter @michaeldwall and Google+. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.