Astronomers have confirmed that a planet orbiting a distant star has a rocky structure similar to that of Earth, a find that shortens the odds on extraterrestrial life being discovered.

New observations of a planet named Corot-7b, which circles a star 500 light years away in the constellation Monoceros, or the Unicorn, have shown that its density is similar to the Earth’s, indicating that it is also a solid, rocky world.

The discovery is important for the prospects of discovering life elsewhere because Corot-7b is the first exoplanet — a planet beyond our solar system — orbiting another star that has been found to have the sort of solid structure that might harbour living things.

Although it is unlikely that the planet itself could be home to living organisms because it is so hot — it is so close to its parent star that scientists have likened it to Dante’s Inferno — the new research suggests that other rocky worlds are probably common.

The discovery of Corot-7b was announced in February after observations by the Corot planet-hunting space observatory. While its diameter was shown then to be about 80 per cent larger than the Earth’s, its mass and, hence, its density could not initially be calculated.

These values have now been worked out from data collected by the High Accuracy Radial Velocity Planet Searcher (Harps) instrument at the La Silla observatory of European Southern Observatory. The planet’s mass is about five times that of Earth, which means that its density is similar to that of our planet.

“This is science at its thrilling and amazing best,” said Didier Queloz, of the Geneva observatory in Switzerland, who led the research team. “We did everything we could to learn what the object discovered by the Corot satellite looks like and we found a unique system.”

Claire Montou, of the Marseilles astrophysics laboratory in France and another member of the team, said that the planet’s mass “is the smallest that has been precisely measured for an exoplanet”. She added: “Moreover, as we have both the radius and the mass, we can determine the density and get a better idea of the internal structure of this planet.”

Details of the planet’s mass and density were announced yesterday at the European Planetary Science Congress in Barcelona and will be published in the journal Astronomy and Astrophysics.

Corot-7b orbits 1.6 million miles (2.5 million km) from its parent star, which is 23 times closer than Mercury, the innermost planet in our solar system, is to the Sun.

“Corot-7b is so close that the place may well look like Dante’s Inferno, with a probable temperature on its ‘day-face’ above 2000C (3,600F) and minus 200C (minus 330F) on its ‘night face’,” Dr Queloz said.

“Theoretical models suggest that the planet may have lava or boiling oceans on its surface. With such extreme conditions, this planet is definitively not a place for life to develop.”

The confirmed existence of a planet with a rocky structure and a density like the Earth’s, however, increases the chances that similar worlds with more favourable conditions for life will be found.

The Corot probe and the Nasa Kepler planet-hunting observatory are currently in orbit looking for such planets.

Alan Boss, of the Carnegie Institution of Washington, who works on the Kepler project, said: “The evidence is becoming overwhelming that we live in a crowded Universe.”

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