Exoplanets HD 85512 b, Gliese 581 d, Kepler-22 b, and Gliese 667C c are the only four current confirmed exoplanets that are potentially habitable.
Here compared with Earth and Mars using the Earth Similarity Index, or ESI (number below the names). This number is a measure of Earth-likeness where Earth is the standard of comparison with an ESI value equal to one. Exoplanets with values above 0.8 can be considered Earth-like planets but those with values down to about 0.7 might still be habitable by microbial life. HD 85512 b, Gliese 581 d, and Kepler-22 b are shown here with dense atmospheres covered with water clouds. Gliese 581 d and Gliese 667C c look redder because they orbit red dwarf stars. The habitability metrics used here only considered the possibility for surface life, as we know it, and not any potential subsurface life, hence Europa, Titan, and Enceladus are not included.
