Though scientists aren't completely sure yet if other planets in our solar system are habitable, they're also looking beyond the solar system to find signs of extraterrestrial life. These exoplanets, or planets that orbit stars other than our sun, have been exciting discoveries in more ways than one.
One of the biggest questions humanity has asked itself is if we are indeed alone in the universe. Many sci-fi books, films, and TV series have explored what it would be like to make contact with extraterrestrial species. If aliens exist, however, where can we find them?
In August of last year, scientists discovered a possibly habitable planet orbiting our nearest neighboring star, the red dwarf star Proxima Centauri. Proxima b is roughly the size of the Earth and lies in the habitable zone of its star system.
This exoplanet is just 4.2 light years away from Earth, so it's basically right next door in cosmological terms. The problem, however, is that Proxima b is too close to its star and may also be tidally locked. This means that one side of the planet perpetually faces the star, making that side extremely hot while the other side is extremely cold.
Just earlier this month, scientists discovered that GJ 1123b has an atmosphere that contains water or methane, or both. This exoplanet orbits another red dwarf star 39 light years away from Earth.
It orbits its star quite closely, so while it's close to Earth in size, it's more like Venus. Scientists are skeptical that GJ 1132b is habitable, since its surface temperature can reach 370ºC. However, scientists did just discovere the planet's atmosphere. It may take more observations to determine how the atmosphere affects the planet's surface temperature. The atmosphere and the presence of water may make the planet cool enough to support life.
The TRAPPIST-1 system made waves when scientists discovered that it hosts at least seven exoplanets, some of which may be habitable. These planets are roughly the size of Earth and Venus, and three of them are in the habitable zone.
TRAPPIST-1 is an ultra-cool dwarf star about 39 light years away from Earth. It's less massive than our sun and is about the size of Jupiter. However, it also emits powerful x-ray and UV radiation flares, which can be quite dangerous. It's still possible that the planets in the habitable zone can support life, but their atmosphere would need to be quite thick.
Kepler 186f is the first among Earth-like exoplanets that scientists discovered. It was this discovery that confirmed to scientists that Earth-like planets exist in the habitable zones of other star systems. Its star, Kepler 186, is also quite similar to our sun.
The problem, however, is that the Kepler 186 system is 500 light years away from Earth. Thus, studying it more closely and looking for signs of life will be difficult even with our best telescopes. For now, we know is that Kepler 186f is 10% larger than Earth and has temperatures similar to those of Mars. Thus, certain microbes may be able to survive on the planet.
Of all the exoplanets on this list, LHS 1140b may have the best chances of supporting life. It orbits in the habitable zone around the red dwarf star LHS 1140, which lies 39 light years away from Earth. Scientists have been calling LHS 1140b a “super-Earth”, a planet that's bigger than Earth but smaller than Uranus or Neptune.
Its orbit is quite close to its star, but the planet has the right temperature for liquid water. Unlike TRAPPIST-1, LHS1140 doesn't produce harmful flares. All these factors make it possible that LHS 1140b is the best candidate for supporting life among possibly habitable exoplanets.
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