News : Scientists say Super-Earth has rocky surface

LONDON (Reuters) - Detailed data about the smallest planet ever found outside our solar system suggest it is a rocky "super-Earth" world very like our own, European astronomers said on Wednesday.

The so-called exoplanet, whose initial discovery was announced in February, has a mass five times that of Earth, which when combined with its radius suggests it has a solid surface and a density similar to our terrestrial home.

"This is science at its thrilling and amazing best," said Swiss astronomer Didier Queloz, the leader of the team that made the observations.

About 330 exoplanets have been found orbiting other stars besides the Earth's sun, most of which are gas giants with characteristics similar to Neptune, which has a mass 17 times that of earth.

But the planet at the center of Wednesday's study -- called CoRoT-7b -- is different. It orbits only 2.5 million kilometres from its star once every 20 hours and has a high temperature between 1,000 and 1,500 Celsius, meaning no life could survive there. Its radius is about 80 percent greater than Earth's.

In a report in the Astronomy and Astrophysics journal, the scientists said their findings put CoRoT-7b into the category of "super-Earth" exoplanets.

About a dozen such "super-Earths" have been detected, but this is the first time that the density has been measured for such a small exoplanet, they said.

The findings are important because they represent the first solid evidence about the mass and density of such a small planet.

To get their measurements, the astronomers used what they dubbed "the best exoplanet-hunting device in the world," called a high accuracy radial velocity planet searcher (HARPS) -- which is a spectrograph attached to the European Southern Observatory's telescope at the La Silla observatory in Chile.

"Even though HARPS is certainly unbeaten when it comes to detecting small exoplanets, the measurements of CoRoT-7b proved to be so demanding that we had to gather 70 hours of observations," said Francois Bouchy, another of the European-wide group of scientists who conducted the study.

Fellow astronomer Artie Hatzes said the work represented a "tour de force" of astronomical measurements.

(Reporting by Kate Kelland; editing by Ben Hirschler)