Goldilocks' planet may be just right for life

• 00:01 25 April 2007
• NewScientist.com news service
• Hazel Muir

Audio: Hear Stéphane Udry discuss this feature as part of SciPod, New Scientist’s weekly podcast.

For the first time, astronomers have spotted a cosy alien planet that might be hospitable to life. The planet is not much bigger than the Earth, and it enjoys balmy temperatures of about 20° C (68° F) as well as spectacular scarlet sunsets.

"It's the smallest, lightest planet known at this time," says Stéphane Udry from the Geneva Observatory in Switzerland. "And it's just at the right distance from its star for liquid water to possibly exist on its surface."

Udry and colleagues discovered the planet using the European Southern Observatory's 3.6-metre telescope in Chile. They monitored a small, dim "red dwarf" star called Gliese 581, which lies 20.5 light years away, and is already known to have a Neptune-class planet.

Subtle "wobbles" of the star suggested that it has two additional planets. One is about eight times as massive as the Earth and orbits once every 84 days. The other may be only five times as massive as the Earth, making it the smallest planet ever found around a normal star.

Just right

Theory predicts that the small planet should be about 50% wider than the Earth and have a rocky surface. It orbits its dim star every 13 days, and the astronomers calculate that it has a pleasant surface temperature of about 0 to 40°C – just right for liquid water, so the planet might be habitable.

"If you take an average value for the amount of starlight heating the planet, you get something like 20° C," Udry told New Scientist. That's similar to the average temperature in New York City, US, in June.

Astronomers have discovered "super-Earths" slightly larger than this one before. However, they are either too hot or too cold for liquid water to exist. The smallest world circling Gliese 581 is a "Goldilocks" planet with the conditions just right for potential life.

Spectacular sunsets

Sunrises and sunsets on the planet must be spectacular. If you could stand on its surface, you would see its red host star looming 10 times wider in the sky than our own Sun appears.

Team member Xavier Delfosse from Grenoble University in France says he hopes that spacecraft missions will probe the world for signs of life over the next decade or two.

"On the treasure map of the universe, one would be tempted to mark this planet with an X," says Delfosse. "Because of its temperature and relative proximity, this planet will most probably be a very important target of the future space missions dedicated to the search for extraterrestrial life."

reposted from: NS
my: highlights / emphasis / key points / comments