First Habitable Planet Found Outside Solar System

[Greg]

A Habitable Exoplanet — for Real This Time
By Lisa Grossman September 29, 2010

After years of saying habitable exoplanets are just around the corner, planet hunters have finally found one. Gliese 581g is the first planet found to lie squarely in its star’s habitable zone, where the conditions are right for liquid water.

“The threshold has now been crossed,” said astronomer R. Paul Butler of the Carnegie Institution of Washington, one of the planet’s discoverers, in a press briefing September 29. “The data says this planet is at the right distance for liquid water, and the right mass to hold on to a substantial atmosphere.”

The discovery is both “incremental and monumental,” comments exoplanet expert Sara Seager of MIT, who was not involved in the new study. When a recent study predicted the first habitable world should show up by next May, Seager rightly said the real answer was more like “any day now.”

“We’ve found smaller and smaller planets that got closer and closer to the habitable zone,” she said. “But this is the first that’s in the habitable zone.”

The new planet is one of six orbiting the star Gliese 581, a red dwarf 20 light-years from Earth. Two of the planet’s siblings, dubbed planets c and d, have also been hailed as potentially habitable worlds. The two planets straddle the region around the star where liquid water could exist — 581c is too hot, and 581d is too cold. But 581g is just right. The discovery will be published in the Astrophysical Journal and online at arxiv.org.

The new planet is about 3 times the mass of Earth, which indicates it is probably rocky and has enough surface gravity to sustain a stable atmosphere. It orbits its star once every 36.6 days at a distance of just 13 million miles. . .


http://www.wired.com/wiredscience/2010/09/real-habitable-exoplanet/