 Gliese 581 g has attracted attention because it would be near the middle of the habitable zone of its parent star . That means it could sustain liquid water on its surface and could potentially host life similar to that on Earth ( the planet is predicted to have temperatures around − 37 to − 11 ° C ) . If it is a rocky planet , favorable atmospheric conditions could permit the presence of liquid water , a necessity for all known life , on its surface . With an estimated mass of 2 @.@ 2 times Earth 's , Gliese 581 g would be considered a Super @-@ Earth and would be the planet closest in mass to Earth known in a habitable zone . This would make it one of the most Earth @-@ like Goldilocks planets found outside the Solar System and one of the exoplanets with the greatest recognized potential for harboring life . 
