Gliese 581c exoplanet, illustration. Gliese 581 c is the second planet discovered in the system and the third in order from the star. With the mass at least 5.5 times that of Earth, it is classified as a super-Earth. Gliese 581c gained interest from astronomers because it was reported to be the first Earth-like planet in the habitable zone of its star, with temperature right for liquid water on its surface. It is tidally locked (always presents the same face to) its star, so if life had a chance to emerge, the best hope of survival would be the terminator zone.