Planet of distant star found, could support life

European astronomers announced Tuesday that they have 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 ranges from freezing to 104 degrees Fahrenheit, the crucial 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.

The discovery was made with the European Southern Observatory’s 12-foot diameter telescope in La Silla, Chile.

Geoffrey Marcy, a University of California at Berkeley astronomer who has discovered most of the so-called exoplanets orbiting other stars, called it “a marvelous discovery … the best case for a habitable planet” so far.

But Marcy and other scientists cautioned against reading too much into the discovery.

Eugene Chiang, a planetary specialist at UC Berkeley, said the Europeans have no proof the planet is rocky or that their estimates of the surface temperature are accurate. “This is a step beyond what’s been done,” he said. “But to say this planet is habitable is a real stretch.”

So far, 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. Because of this, most of the known exoplanets are huge and very close to their stars.

The Holy Grail for planet hunters is finding a rocky planet about the size of Earth orbiting a star similar to the sun in the so-called Goldilocks zone – not too hot, not too cold.

The European team said the new planet is the closest match so far. Even though the planet is closer to its star than Mercury is to our sun, Gliese 581 is a much cooler star.

The new planet, which completes one orbit every 13 days, is the third found around Gliese 581, including one Neptune-size world that completes an orbit every five days.

Xavier Bonfils, of Lisbon University, said red dwarfs are ideal targets for planet-finding efforts “because they emit less light, and the habitable zone is thus much closer than it is around the sun.”

Gliese 581 is among the 100 stars closest to our solar system. The vast majority are red dwarfs. The sun is a medium-size yellow star.