The year 2021 gave truth-seekers and alien hunters no shortage of mysteries to ponder. But it also gave them answers — from a hotly anticipated Pentagon report on military UFO sightings, to new insights on habitable exoplanets, to the truth about a so-called "alien signal" from the sun's nearest neighboring star. Here are 9 things we learned about aliens (and where to look for them) in 2021.
1. UFOs are real (and the government knows it)
In June, the Pentagon released a highly anticipated report detailing 144 UFO encounters between 2004 and 2021. The report was meant to assess "the threat posed by unidentified aerial phenomena (UAP)," and officially confirmed several UFO sightings that had, until then, only been shared through viral media. On one hand, the brief, 9-page assessment confirmed that "most of the UAP reported probably do represent physical objects," which range from birds and balloons to foreign surveillance equipment and top-secret U.S. government projects. However, anyone hoping for an acknowledgement of extraterrestrial intelligence may have been let down when the report failed to link any of the 144 encounters to alien activity.
2. Black holes could be alien powerhouses
While alien hunters spend plenty of time searching for habitable planets beyond our solar system, a study published in July in the journal Monthly Notices of the Royal Astronomical Society warns that scientists shouldn't overlook nature's most extreme objects: Black holes. Because black holes can radiate up to 100,000 times more energy than a star like our sun, they may make tempting targets for alien civilizations looking to power their interstellar enterprises, the study authors wrote. To do this, aliens could use high-tech structures called Dyson spheres (giant, energy-siphoning orbs first proposed in the 1960s) to steal energy from the disc of white-hot matter swirling around a black hole's horizon, then radiate that energy outward into space. That re-radiated energy would create a distinct wavelength signature that astronomers could detect from Earth, the study authors suggested. The researchers are currently developing algorithms to search through existing telescope data in search of those telltale signatures.
3. Alien planets may look nothing like Earth
Typically, the search for alien life begins with the search for Earth-like planets — but there may be another class of alien world that is just as conducive to life, a study published in the Astrophysical Journal in August contends. "Hycean" planets, which are up to 2.5 times larger than Earth and sport huge oceans of liquid water beneath hydrogen-rich atmospheres, could be the ideal spot for microbial life similar to the "extremophiles" that thrive in some of Earth's harshest environments (such as hydrothermal vents), the study authors said. Not only are these planets abundant in the Milky Way galaxy, but they are also incredibly diverse, some orbiting very close to their host star, others orbiting far away. Both could potentially host itty-bitty life beneath their waves, the authors wrote, meaning there may be a whole new avenue of exploration for alien planet hunters.
4. One of Saturn's moon still holds potential for life
The methane wafting from Enceladus, Saturn's sixth largest moon, may be a sign that life teems in the moon's subsurface sea, a June study found. In 2005, NASA's Cassini Saturn orbiter discovered geysers blasting particles of water ice into space from "tiger stripe" fractures near Enceladus' south pole. That material is thought to come from a huge ocean of liquid water that sloshes beneath the moon's icy shell — but it wasn't just water the orbiter found; numerous other compounds, including dihydrogen (H2) and a variety of carbon-containing organic compounds, including methane (CH4), also appeared in the geysers.
In the new study, researchers ran a series of models to determine whether those compounds could be evidence of microbes that "eat" dihydrogen and produce methane as waste. The team found that methane-farting microbes could indeed be contributing to the planet's gassy geysers — meaning life can't be ruled out on the icy moon.
5. Scientists may be ignoring "alien junk" in our own solar system
According to Harvard astrophysicist Avi Loeb's recent book "Extraterrestrial: The First Sign of Intelligent Life Beyond Earth" (published in January by Mariner Books), the strange, cigar-shaped object 'Oumuamua — which zoomed through our solar system in 2017 — is almost certainly a piece of alien technology. In his book, Loeb argues that the object's unusual, elongated shape (unlike any known comet), extreme brightness and apparent acceleration away from the sun suggest that 'Oumuamua is not natural in origin, but a piece of alien technology — possibly jettisoned into our solar system accidentally.
"A buoy. A grid of pods for communication… Other intelligent living organisms' defunct technology or discarded technological trash," Loeb wrote. "These all are plausible explanations for the 'Oumuamua mystery — plausible because here on Earth, humanity is already doing these things, albeit on a far more limited scale." (A majority of astronomers who have studied the object favor natural explanations, calling it a cosmic "dust bunny" or just a really odd comet).
6. Thousands of alien worlds could have watched humans grow up
While human efforts to find alien civilizations among the stars have only kicked off in the last century or so, more than 1,700 alien civilizations could have been watching us for thousands of years prior. According to a study published in June in the journal Nature, 1,715 nearby star systems have had a perfect viewing angle of Earth over the last 5,000 years — and more than 1,400 of them still have a clear view today.
All of these stars sit within about 300 light-years of our planet, and 75 of them orbit less than 100 light-years away. Given that humans have been transmitting radio signals for about 100 years, any of those 75 star systems are near enough that "our radio waves would have washed over them already," lead study author Lisa Kaltenegger, an associate professor of astronomy and director of the Carl Sagan Institute at Cornell University, told Live Science at the time. Whether or not any hypothetical civilizations living in those star systems want to communicate with us is another question.
7. There's no "best" way to communicate with aliens
If aliens are watching us from relatively closeby, what's the best way to tell them where we live? Live Science writer Joanna Thompson investigated this question in December, finding that no one method is flawless. On one hand, radio waves are a tempting way to communicate with extraterrestrials because these signals fit in a convenient gap in the electromagnetic spectrum called the "water hole" — a frequency between 1420 and 1720 megahertz that's relatively free of cosmic background noise.
On the other hand, radio waves broaden as they travel, meaning any message we send will become more diluted the farther from Earth it gets. Laser light does not have this problem — however, laser signals require incredible precision, and are unlikely to reach any alien observers unless we target our message directly to their star system. Both methods have their advantages — and neither are perfect.
8. Our own technology might be getting in the way
On April 29, 2019, astronomers detected a signal beaming toward Earth, it seemed, from Proxima Centauri — the nearest star system to our sun and home to at least one potentially habitable planet. Because the signal fell into a narrow band of radio waves that are rarely made by human aircraft or satellites, researchers interpreted it as a possible sign of alien technology. But the signal never repeated — and a study published this October in the journal Nature Astronomy explains why: The signal was actually coming from a malfunctioning computer or cellular device located near the telescope that detected it.
In the new study, the researchers looked over the 2019 data again and found several "lookalike" signals that seemed to be missing components of the so-called alien transmission; together, these signals fit a range of frequencies "consistent with common clock oscillator frequencies used in digital electronics," the researchers wrote. In other words, this alien message seems to have been a human computer on the fritz — but studying and identifying it still gives scientists valuable experience in separating real deep-space signals from Earthly noise.
9. Alien "abductions" could be lucid dreams
Lucid dreaming, in which people are partially aware and can control their dreams during sleep, could explain so-called alien abduction stories, a study from July suggests. Claims of such abductions date to the 19th century; the circumstances of the kidnappings often sound dreamlike and trigger feelings of terror and paralysis. Certain dream states are also known to produce such feelings, so Russian researchers wondered whether dream experiments could provide clues about alleged extraterrestrial experiences.
The scientists prompted 152 lucid dreamers to dream about encounters with aliens or UFOs, and found that a number of sleepers reported dreams that resembled actual descriptions of alleged alien abductions. Of those who described their dream encounters as "realistic," 24% also experienced sleep paralysis and intense fear. Such emotions often accompany reports of supposed alien abductions, and though individuals who describe being kidnapped by aliens might truly believe that what they experienced was real, these people were likely experiencing an extraterrestrial meeting while in a lucid dream, the study authors reported.
Originally published on Live Science.
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Brandon is the space/physics editor at Live Science. His writing has appeared in The Washington Post, Reader's Digest, CBS.com, the Richard Dawkins Foundation website and other outlets. He holds a bachelor's degree in creative writing from the University of Arizona, with minors in journalism and media arts. He enjoys writing most about space, geoscience and the mysteries of the universe.