It's Earth, but not as we know it

from correspondents in Paris
April 25, 2007 12:28pm

ASTRONOMERS say they have discovered a "super-Earth" more than 20 light years away that is the most intriguing world found so far in the search for extraterrestrial life.

About five times the mass of Earth, the planet orbits a cool, dim red dwarf' star in the constellation of Libra, the team from the European Southern Observatory (ESO) said.

The star, Gliese 581, has already been identified as hosting a planet similar in size to Neptune, the frigid gas giant on the edge of our own solar system.

The new planet is 14 times closer to Gliese 581 than Earth is to the sun. But because Gliese 581 is so cool, the planet is not scorched by solar radiation. It zips around the star at express speed, making just 13 days to complete an orbit.

"We have estimated that the mean temperature of this super-Earth lies between 0 and 40 degrees Celsius, and water would thus be liquid,'' said lead researcher Stephane Udry of Switzerland's Geneva University.

"Moreover, its radius should be only 1.5 times the Earth's radius, and models predict that the planet should be either rocky - like our Earth - or covered with oceans.''

"Liquid water is critical to life as we know it,'' said Xavier Delfosse, a team member from France's Grenoble University.

"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 extra terrestrial life," he said.

"On the treasure map of the Universe, one would be tempted to mark this planet with an X.''

In 1995, two astronomers, also at Geneva, spotted the first extrasolar planet, a term for a planet orbiting a star other than our own. Since then, 227 such planets have been spotted, according to the Extrasolar Planets Encyclopaedia.

Gliese 581 is among the 100 closest stars to us. Its red dwarf monicker comes from the fact that it is only a third of the mass of the sun.

Because such stars emit far less heat, they offer a far greater chance of having planets in the so-called Goldilocks zone where liquid water - and thus the potential for life - can exist.

Even though Gliese 581 offers such promise, it would be impossible for mankind to reach it - or even send an unmanned scout probe - using current technology.

Chemical rockets generate only a fraction of the light speed needed to get there within a human timescale.

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