Gliese 581c

In April 2007 the Geneva Observatory in Switzerland announced the discovery of a "super-earth" extrasolar planet orbiting the red dwarf star Gliese 581. Dubbed Gliese 581 c, it's been called a super-earth because it is one of the few known extrasolar planets that has a mass near Earth's, and the only one to occupy its sun's "habitable zone."

Gliese 581 c is believed to be about five times more massive than the Earth with a diameter about half-again as large as Earth's. Depending upon the planet's composition, whether mostly rock or a combination of rock a water, a visitor would experience a surface gravity between 1.25 to 2.2 times the Earth's. Gliese 581 c is about 20 light years away, a "next door neighbor" in stellar terms, but far beyond the reach of human visitors with today's technology.

There is special interest in Gliese 581 c because it is the only known extrasolar planet where liquid water--a necessary ingredient for life as we know it--could exist. Surface temperatures are believed to range between the freezing point of water to about 100° F. However, there are other factors that could affect these values, including the possibility that Gliese 581 c always keeps the same side facing its host star, with the result that one side would become extremely hot while the other extremely cold.

In this image from the surface of Gliese 581 c, its red dwarf host hangs low in the sky over a rocky and watery terrain. This sun has a diameter and radius about a third that of the earth's sun's and it is only about 1/100th as bright. It appears large in the sky because Gliese 581 c orbits relatively close to this red dwarf, completing an orbit in only 14 days.