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They believe the new world, called Corot-9b, could become a "Rosetta stone" helping them to understand other "exoplanets" elsewhere in the galaxy.

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Dr Hans Deeg, one of the scientists from the Institute of Astrophysics of the Canaries in Tenerife, said: "Corot-9b is the first exoplanet that really does resemble planets in our solar system. It has the size of Jupiter and an orbit similar to that of Mercury."

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The planet was detected by the CoRoT space telescope operated by the French space agency, CNES.

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Its Sun-like parent star, Corot-9, is 1,500 light years from Earth in the constellation of Serpens, the Snake.

More than 400 exoplanets have been discovered to date, but most are so-called "hot Jupiters" - gas giants that hug their parent stars in close orbits and have surface temperatures of 1,000C or more.

These are the easiest planets to find using the common method of measuring the "wobble" their gravity gives their parent stars.

About 70 exoplanets have been found using a different method which relies on the planet passing in front of its star, or "transiting". The planet reveals itself by blotting out some of the star's light causing it to dim.

Corot-9b was identified by the transit method. The planet took eight hours to pass in front of its star, which provided astronomers with a lot of information.

The planet turned out to be unusual because it was not a "hot" Jupiter. Depending on the extent of reflective clouds in its atmosphere, it has a surface temperature of between minus 20 and 160C.

Dr Didier Queloz, from the University of Geneva in Switzerland and co-author of the research published today in the journal Nature, said: "Our analysis has provided more information on Corot-9b than for other exoplanets of the same type.

"It may open up a new field of research to understand the atmospheres of moderate and low-temperature planets, and in particular a completely new window in our understanding of low-temperature chemistry."

Dr Claire Moutou, from the Astrophysical Laboratory of Marseille, France, another member of the 60-strong international team, said: "It is bound to become a Rosetta stone in exoplanet research."

The planet was spotted by CoRoT in 2008. Land-based astronomers manning the 3.6 metre European Southern Observatory at La Silla, Chile, followed up the discovery by looking in detail at the star system.

Using an instrument called HARP which measures light wavelengths they confirmed that Corot-9b was an exoplanet about 80% as massive as Jupiter.