Newfound planet could foster life, astronomers say

April 25, 2007|By Dennis O'Brien | Dennis O'Brien,Sun reporter

European astronomers have found what could be the first habitable planet outside our solar system, a sphere a bit bigger than Earth covered by rocks or oceans, 20.5 light-years away.

Researchers aren't sure whether the planet has oxygen, carbon or other essential building blocks of life. But it orbits at the right distance from its star to make conditions ripe for an essential ingredient to life as we know it.

"The temperature is right to have water," said Stephane Udry, an astronomer at the Geneva Observatory in Switzerland and lead author of the report published today as a letter to the editor in the journal Astronomy and Astrophysics.

Experts say the discovery represents a breakthrough because even if life is not found on the planet, astronomers will soon find others like it.

"It's the dawn of the era of finding planets that are habitable," said Sara Seager, a planetary scientist at the Massachusetts Institute of Technology.

So little is known about the planet that it is difficult to speculate about the possibility of life there, scientists say. In fact, the search for extrasolar planets is a relatively new field for astronomers: The first weren't discovered until the 1990s.

Since then, more than 200 have been detected, but until now, none has been anything like Earth. Almost all are gas giants the size of Jupiter, but orbiting so close to their stars that their surfaces are as hot as skillets.

Seager cautioned that details about the size and temperature of the planet are based on computer models generated from data collected by observations of the star the planet orbits - and not by observing the planet itself. She put the odds of its being habitable at 50-50.

"Before you get too excited, you should call it `the first potentially habitable planet,'" she said.

The planet is designated as Gliese 581c, based on the red dwarf star in the constellation Libra that it orbits every 13 days. The planet's radius is about 50 percent greater than the Earth's, and its mass is five times greater.

The distance from Gliese 581c to the star it orbits is about 6.6 million miles. Earth, by comparison, is 93 million miles from the sun.

Because the red dwarf is dimmer and cooler than our sun, researchers estimate that temperatures on the planet range from 32 degrees to 104 degrees Fahrenheit. They estimate that the planet's gravity is about twice that on Earth.

That means your weight would double there - and that many creatures probably would be "stockier" than our life forms, said Frank Drake, director of the Search for Extra Terrestrial Life Institute's Center for the Study of Life in the Universe.

"Birds would have a harder time flying. They'd need larger wings," Drake said. "But fish would be largely unaffected."

"You wouldn't want to fall down in that gravity," said Marc Kuchner, who studies distant planets at the NASA Goddard Space Flight Center in Greenbelt. "Snakes would be OK."

The discovery of a potentially habitable planet orbiting a red dwarf is encouraging because scientists weren't sure whether the so-called "M Class" stars had orbiting planets.

"Because this planet was found orbiting a red dwarf, a common type of star, it increases the likelihood that there are other planets like it elsewhere in the universe," Drake said.

The planet's strong gravity probably gives it a slight advantage in fostering life, because that makes it more likely to retain water molecules and life-forming elements such as oxygen and carbon, said Dirk Schulze-Makuch, an astrobiologist at Washington State University. Mars, for example, lost most of its atmosphere in its youth because its small size meant less gravitational force, so that many life-forming molecules were dispersed into space.

But having an atmosphere doesn't necessarily mean a habitable planet, he said. Venus has a carbon dioxide atmosphere that produces such pronounced greenhouse effects that its surface is far too hot for life.

"This is a great discovery, a really great discovery," he said. "It has a potential for life to be there. But more has to be known for us to determine if life even exists there and what kind of life it may be."

The planet's proximity to its star also means that it could be tidally locked, keeping the same face toward it at all times. That would diminish - but not rule out - the chance of life.

"We've found that life finds a way to make it in some pretty extreme conditions," said Nancy Y. Kiang, a biometeorologist who has studied the potential color schemes of extraterrestrial plants at NASA's Goddard Institute for Space Studies.

With light from a red dwarf star, plants on Gliese 581c would have dark pigments that probably would look black or very dark to the human eye, Kiang said.

To harbor life, the planet would have to be a certain age. Photosynthesis started things brewing on Earth about 3.8 billion years ago, almost a billion years after our planet was formed, Kiang said.

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