Earth-sized planet found

HATFIELD (England) - IN A discovery that one expert called 'extraordinary', European astronomers reported finding one planet close to Earth's size in a different solar system and realizing that another planet could possibly sustain a large ocean.

European researchers said on Tuesday that not only had they found the smallest exoplanet ever, called Gliese 581 e, but they realized that a neighbouring planet discovered earlier, Gliese 581 d, was in the prime habitable zone for potential life.

'The Holy Grail of current exoplanet research is the detection of a rocky, Earth-like planet in the 'habitable zone,'' said Michel Mayor, an astrophysicist at Geneva University in Switzerland.

Exoplanets are planets outside our solar system. Gliese 581 e is only 1.9 times the size of Earth - while previous planets found outside our solar system are closer to the size of massive Jupiter, which NASA says could swallow more than 1,000 Earths.

Gliese 581 e sits close to the nearest star, making it too hot to support life. Still, Mr Mayor said its discovery in a solar system 20 light years away from Earth is a 'good example that we are progressing in the detection of Earth-like planets.'

Scientists also discovered that the orbit of planet Gliese 581 d, which was found in 2007, was located within the 'habitable zone' - a region around a sun-like star that would allow water to be liquid on the planet's surface, Mr Mayor said.

He spoke at a news conference on Tuesday at the University of Hertfordshire during the European Week of Astronomy and Space Science.

Fellow astronomer and team member Stephane Udry said Gliese 581 d is probably too large to be made only of rocky material, adding it was possible the planet had a 'large and deep' ocean.

'It is the first serious 'water-world' candidate,' Mr Udry said. Mr Mayor's main planet-hunting competitor, Geoff Marcy of the University of California, Berkeley, praised the find of Gliese 581 e as 'the most exciting discovery' so far of exoplanets.

'This discovery is absolutely extraordinary,' Mr Marcy told The Associated Press by e-mail, calling the discoveries a significant step in the search for Earth-like planets. -- AP.