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Hunting for alien planetsFor years, astronomers have scoured the cosmos for Earth-like planets in alien star systems, in hopes of finding a habitable world where life could exist. This hunt has since turned up thousands of planetary candidates — some with conditions that could be similar to Earth, and others with more of a wild streak. Here are some of the most bizarre Earth-like planets.
Earth's seven sistersSlide 2 of 19
Earth's seven sisters
A motherlode of exoplanets (seven, to be clear) were unveiled in February 2017 in the journal Nature. An international team of astronomers discovered the seven-planet system, located just 40 light-years away from Earth, orbiting their parent star, an ultracool dwarf star known as TRAPPIST-1. At least three of these rocky orbs support oceans on their surface, the discoverers said.
The astronomers discovered the planets using the so-called transit method, measuring the dip in the parent star's light output as each of the seven planets passed in front of it. The method revealed that at least the six inner planets in the system are comparable in size and temperature to Earth.
"This is an amazing planetary system — not only because we have found so many planets, but because they are all surprisingly similar in size to the Earth," lead study author Michael Gillon, of the STAR Institute at the University of Liege in Belgium, said in a statement.
The discovery also has implications for how astronomers view the Milky Way.
"In the past few years, evidence has been mounting that Earth-sized planets are abundant in the galaxy, but Gillon and collaborators' findings indicate that these planets are even more common than previously thought," Ignas Snellen, an astrophysicist at Leiden University in the Netherlands wrote in a related News and Views piece published in the same issue of Nature.Slide 3 of 19
Proxima Centauri bSlide 4 of 19
Proxima Centauri bScientists reported strong evidence of a newfound planet in our own backyard (well, sort of). The alien planet orbits Proxima Centauri, the closest star to our sun. Located just 4.2 light-years away, the planet is close, but it took a lot of creative analysis to make it visible to scientists. [Video: Alien World 'Proxima b' Around Nearest Star Could Be Earth-Like]
Proxima Centauri sometimes approaches Earth, and other times, it moves away, at roughly human walking speed of 3.1 mph (5 km/h). Researchers analyzed the tiny Doppler effect, or change in the frequency of the star's signal as it moved toward and away from Earth. The signal revealed a potential planet about 1.3 times the size of Earth.
Proxima Centauri is an active star with solar flares that can disguise themselves as planetary activity, making it challenging for astronomers to study the system. The team said it has accounted for that by excluding data from when the star was most active.Slide 5 of 19
The TRAPPIST-1 planetsSlide 6 of 19
The TRAPPIST-1 planetsAn ultracool star called TRAPPIST-1 (also known as 2MASS J23062928-0502285) hosts at least three Earth-like planets, according to a recent study published May 2 in the journal Nature. The worlds are similar in size and temperature to Venus and Earth, and are located just 40 light-years away.
The scientists spotted the infrared signal from TRAPPIST-1 fading and brightening regularly, which suggested that several objects might be passing in between the star and our planet. The three planets orbit the parent star every 1.5 Earth days, 2.4 Earth days, and four to 73 Earth days, respectively.
When the planets were discovered, study co-author Julien de Wit, a postdoctoral student at MIT, said in a statement that they are so close to Earth that scientists may be able to probe the planets' atmospheres.Slide 7 of 19
Kepler-438bSlide 8 of 19