Gliese 581 c is a planet orbiting the red dwarf star Gliese 581. It is the second planet discovered in the system and the third in order from it's parent star. With a mass at least 5.6 times that of the Earth, it is classified as a super-Earth (a planet of 1 to 10 Earth masses). It was the smallest known extrasolar planet around a main sequence star, but on April 21, 2009, another planet orbiting Gliese 581, Gliese 581 e, was announced with a mass of 1.9 Earth masses, which is now the smallest known extrasolar planet around a main sequence star.
Gliese 581 c initially generated interest because it was originally reported to be the first potentially Earth-like planet in the habitable zone of its star, with a temperature and distance right for liquid water on its surface and potentially capable of supporting extremophile forms of Earth-like life. However, further research on the potential effects of the planetary atmosphere casts doubt upon the habitability of Gliese 581 c and indicates that the fourth planet in the system, Gliese 581 g, is a better candidate for habitability. In astronomical terms, the Gliese 581 system is relatively close to Earth, at 20 light years (192 trillion km or 119 trillion miles) in the direction of the constellation of Libra, it is the 87th closest known star system to the Sun.