A potentially life-friendly, a planet must be relatively small and orbit in the “habitable zone” of its star, which is loosely defined as a location where water can exist in liquid form on a world’s surface.According to NASA, these are the closest contenders for the Earth 2.0
This exoplanet, which lies just 22 light-years from Earth, is at least 4.5 times as massive as Earth, and researchers aren’t sure whether or not it’s rocky. Gliese 667Cc completes one orbit around its host star in a mere 28 days, but that star is a red dwarf considerably cooler than the sun, so the exoplanet is thought to lie in the habitable zone.
Kepler-22b lies 600 light-years away. It was the first Kepler planet found in the habitable zone of its parent star, but the world is considerably larger than Earth — about 2.4 times our planet’s size. It’s unclear if this “super-Earth” planet is rocky, liquid or gaseous. Its orbit is about 290 days long.
Kepler-69c, which is about 2,700 light-years away, is about 70 percent larger than Earth. So, once again, researchers are unsure about its composition. The planet completes one orbit every 242 days, making its position within its solar system comparable to that of Venus within ours. However, Kepler-69c’s host star is about 80 percent as luminous as the sun, so the planet appears to be in the habitable zone.
This planet is about 40 percent larger than Earth and orbits a star much cooler than our sun. Its 267-day orbit, however, puts Kepler-62f squarely within the habitable zone. The Kepler-62 system lies about 1,200 light-years away.
This planet is at most 10 percent larger than Earth, and it also appears to reside in the habitable zone of its star, though on the zone’s outer edge; Kepler-186f receives just one-third of the energy from its star that Earth gets from the sun. Kepler-186f’s parent star is a red dwarf, so the alien world is not a true Earth twin. The planet lies about 500 light-years from Earth
This world, whose discovery was announced last month, is the most Earth-like planet found so far, NASA officials say. Its parent star is very similar to our sun, and the planet orbits in the habitable zone. At 1.6 times the size of Earth, Kepler-452b has a “better than even chance” of being rocky, its discoverers have said. Kepler-452b resides 1,400 light-years from Earth.