This planet could have a life of its own
European astronomers announced Tuesday that they had discovered the first planet beyond our solar system that orbits in a "sweet spot" zone where life could exist.
The planet, about five times as massive as Earth, orbits Gliese 581, a red dwarf star about 20 light-years from our solar system.
The team of Swiss, French and Portuguese scientists who found the planet estimate its surface temperature at freezing to 104 degrees Fahrenheit, a range in which water can exist as a liquid.
"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," said Xavier Delfosse, an astronomer from Grenoble University in France.
"On the treasure map of the universe, one would be tempted to mark this planet with an X."
The discovery was made with the European Southern Observatory's 12-foot diameter telescope in La Silla, Chile. The planet was first detected by the telescope's HARPS Spectrograph, which analyzes light from distant astronomical objects.
Geoffrey Marcy, a UC Berkeley astronomer who has discovered most of the so-called exoplanets orbiting other stars, called it "a marvelous discovery
But Marcy and other scientists cautioned against reading too much into the discovery.
Eugene Chiang, a planetary specialist at UC Berkeley, said the Europeans had no proof the planet was rocky, or that their estimates of the surface temperature were accurate.
"This is a step beyond what's been done," he said. "But to say this planet is habitable is a real stretch."
If alien astronomers saw Venus from afar, for instance, they would not be able to tell that a runaway greenhouse effect had created an unlivable hell of a world, with temperatures of 750 degrees Fahrenheit.
"The surface temperature depends on the atmosphere, and they don't know what the atmosphere is made of," Chiang said of the new planet.
More than 200 exoplanets have been found, most by Marcy's team and the European team that announced this latest find.
The vast majority have been gas giants, orbiting so close to their home stars that anything alive, at least as we understand it, would be cooked.
Most exoplanets are too distant to be seen directly. Their existence must be inferred by observing the slight wobble they cause in their home stars.
