1. Gliese 581g It was discovered in 2010, but there has been difficulty in getting it confirmed. It orbits its parent star, Gliese 581, about every 30 days in the constellation Libra.According to researchers it could sustain liquid water on its surface and could potentially host life similar to that on Earth.
It is the top candidate for alien life. It is about 20 light-years away from Earth's sun, and is two to three times as massive as Earth.