The planet, found by astronomers at the University of California, Santa Cruz, and the Carnegie Institution of Washington, is orbiting in the middle of the "habitable zone" of the red dwarf star Gliese 581, which means it could have water on its surface.

Liquid water and an atmosphere are necessary for a planet to possibly sustain life, even it it might not be a great place to live, the scientists said.

The scientists determined that the planet, which they have called Gliese 581g, has a mass three to four times that of Earth and an orbital period of just under 37 days. Its mass indicates that it is probably a rocky planet and has enough gravity to hold on to an atmosphere, according to Steven Vogt, professor of astronomy and astrophysics at the University of California, Santa Cruz, and one of the leaders of the team that discovered the planet. [ YAHOO NEWS ]