Surface of extrasolar planet Gliese 581c, artwork. An active volcano is at right, and the plant's parent star is seen in the sky. Gliese 581c is the most Earth-like alien planet yet discovered. It is one of three orbiting the red dwarf star Gliese 581 (the others are seen in the sky). Gliese 581c is 1.5 times Earth's diameter and five times its mass, and it lies in the star's habitable zone. This is a region around a star where the surface temperature of a planet is suitable for liquid water. Gliese 581c is fourteen times closer than Earth is to the Sun, but the low heat output of the red dwarf makes its habitable zone much closer to it than the Sun's. Gliese 581 lies about 20.5 light years from Earth in the constellation Libra. The planet's discovery was announced in 2007.