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Astronomers spy an Earthlike planet, in theory

It's a blip of light, but distant 581 c stirs excitement

An illustration showed the possible configuration of the planetary system around the red dwarf Gliese 581 (right). (European Southern Observatory/associated press)

WASHINGTON -- For the first time, astronomers have discovered a planet outside our solar system that is potentially habitable, with Earth like temperatures, a find researchers described yesterday as a big step in the search for "life in the universe."

The planet is just the right size, might have water in liquid form, and in galactic terms is relatively nearby at 120 trillion miles away. But the star it closely orbits, known as a red dwarf, is much smaller, dimmer, and cooler than our sun.

There's still a lot that is unknown about the newly discovered planet, which could be deemed inhospitable to life once more is known about it. And it's worth noting that scientists' requirements for habitability count Mars in that category: a size relatively similar to Earth's with temperatures that would permit liquid water; however, this is the first body outside our solar system that meets those standards.

"It's a significant step on the way to finding possible life in the universe," said Michel Mayor, an astronomer at the University of Geneva and one of 11 European scientists on the team that found the planet. "It's a nice discovery. We still have a lot of questions."

The results of the discovery have not been published but have been submitted to the journal Astronomy and Astrophysics.

Alan Boss, who works at the Carnegie Institution of Washington, where a US team of astronomers competed in the hunt for an Earth like planet, called it "a major milestone in this business."

The planet was discovered by the European Southern Observatory's telescope in La Silla, Chile, which has a special instrument that splits light to find wobbles in different wave lengths. Those wobbles can reveal the existence of other worlds.

What they revealed is a planet circling the red dwarf star Gliese 581. Red dwarfs are low-energy, tiny stars that give off dim red light and last longer than stars like our sun. Until a few years ago, astronomers didn't consider these stars to be possible hosts of planets that might sustain life.

The discovery of the planet, named 581 c, is sure to fuel studies of planets circling similar dim stars. About 80 percent of the stars near Earth are red dwarfs.

The new planet is about five times heavier than Earth. Its discoverers aren't certain whether it is rocky like Earth or is a frozen ice ball with liquid water on the surface. If it is rocky, as the prevailing theory proposes, it has a diameter about 1.5 times that of Earth.

Based on theory, 581 c should have an atmosphere. The research team believes that its average temperature is somewhere between 32 and 104 degrees, and that hypothesis set off celebrations among astronomers.

Until now, all 220 planets that astronomers have found outside our solar system have had the "Goldilocks problem." They've been too hot, too cold, or too big and gaseous, like Jupiter.

The new planet seems just right -- or at least that's what scientists think.

The new planet's star system is a mere 20.5 light-years away, making Gliese 581 one of the 100 closest stars to Earth. It's so dim, you can't see it without a telescope, but it's in the constellation Libra, which is low in the southeastern sky at midevening in the Northern Hemisphere.