They believe the new world, called Corot-9b, could become a ''Rosetta stone'' helping them to understand other ''exoplanets'' elsewhere in the galaxy. The planet was detected by the CoRoT space telescope operated by the French space agency, CNES. 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. 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.