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                             Most Earthlike Planet Yet Found May Have Liquid Oceans






Kate Ravilious
for National Geographic News
April 21, 2009

It probably wouldn't feel exactly like home. But the planet known as Gliese 581d has a lot more in common with Earth than astronomers first thought.

New measurements of the planet's orbit place it firmly in a region where conditions would be right for liquid water, and thus life as we know it, astronomer Michel Mayor, from Geneva University in Switzerland, announced today.
 


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"It lies in the [life-supporting] habitable zone, and it could have an ocean at its surface," Mayor said during the European Week of Astronomy and Space Science conference, being held this week at the University of Hertfordshire in the U.K.

First discovered in 2007, Gliese 581d was originally calculated to be too far away from its host star—and therefore too cold—to support an ocean.

But Mayor and colleagues now show that the extrasolar planet, or exoplanet, orbits its host in 66.8 days, putting it just inside the cool star's habitable zone.

At the same time, Mayor and colleagues announced that they have spotted a fourth planet orbiting in the Gliese 581 star system—and it's the lightest exoplanet found so far.

The planet, dubbed Gliese 581e, is only about twice the mass of Earth and is the closest planet to the star, completing its orbit in about 3.15 days.

"It brings down the mass [of the lightest known exoplanet] by more than a factor of two. The previous smallest was around five Earth masses," said Andrew Collier Cameron, an astronomer at the University of Saint Andrews in the U.K. who was not involved in the find.



(Related: "Mysterious 'Super Earth' Is Smallest Known Exoplanet?")