Earthlike planet is found

Published 9:00 pm Tuesday, April 24, 2007

WASHINGTON – For the first time astronomers have discovered a planet outside our solar system that is potentially habitable, with Earthlike temperatures, a find researchers described Tuesday as a big step in the search for “life in the universe.”

The planet, named 581 c, 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 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 outside our solar system that meets those standards.

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

Alan Boss, who works at the Carnegie Institution of Washington where a U.S. team of astronomers competed in the hunt for an Earthlike planet, called it “a major milestone in this business.”

The planet, discovered by the European Southern Observatory’s telescope in La Silla, Chile, circles 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 as possible hosts of planets that might sustain life.

The planet is about five times heavier than Earth. Its discoverers aren’t certain if it is rocky like Earth or if its a frozen ice ball with liquid water on the surface.

If it is rocky like Earth, which is what the prevailing theory proposes, it has a diameter about 1 1/2 times bigger than our planet. If it is an iceball, as Mayor suggests, it would be even bigger.

Based on theory, 581 c should have an atmosphere, but what’s in that atmosphere is still a mystery and if it’s too thick that could make the planet’s surface temperature too hot, Mayor said.

However, the research team believes the average temperature to be somewhere between 32 and 104 degrees, and that set off celebrations among astronomers.

Besides having the right temperature, 581 c is probably full of liquid water, hypothesizes Geneva astronomer Stephane Udry, the discovery team’s lead author.

But that is based on theory about how planets form, not on any evidence, he said.