A Second Earth?

Gliese581solarsystem: Three planets orbit the small red star Gliese 581, including the most Earthlike planet ever found outside our solar system, GL581c (in the foreground). Credit: ESO, artist's rendering.

GL581c: GL581c orbits its star at a distance of about 6 million miles. Our hot Sun would incinerate a planet at that distance, but red dwarf stars emit less energy, so even this close orbit should allow temperatures on the planet's surface to stay between 0ø and 40øC (32ø-104øF), the perfect range for liquid water. Credit: ESO, artist's rendering.

On April 25, astronomers from the Geneva Observatory identified a new planet orbiting a star in the constellation Libra. Since 1995, astronomers have found more than 230 planets orbiting distant stars, so this new discovery may have gone largely unnoticed if it weren't for one tantalizing detail-this particular planet is the most Earthlike body ever found outside our solar system.

Provisionally named GL581c, the planet orbits a small red star called Gliese 581 once every 13 days. It orbits within the "Goldilocks Zone," where temperatures are "just right" for water-and thus life-to exist. Although scientists don't yet know what GL581c is made of, its mass is about five times that of our planet. If it's a solid, rocky object like Earth, its diameter would be about 1.5 times that of Earth and it would have about twice the gravity.

Gliese581: Part of the constellation Libra, Gliese 581 is located only 20.5 light years away from Earth (about 120 trillion miles). Credit: Digital Sky Survey.