Gliese 581 (pronounced /ˈɡliːzə/) is a red dwarf star with spectral type M3V, located 20.3 light years away from Earth in the constellation Libra. Its estimated mass is about a third of that of the Sun, and it is the 89th closest known star system to the Sun. Observations suggested that the star has six planets: Gliese 581 e, b, c, g, d and f. Significantly, planet g would be close to the middle of the star's habitable zone.