No sign of Avatar's blue-skinned Na'vi aliens, but Europe's CoRoT space telescope Wednesday yielded the discovery of a Jupiter-sized world orbiting a "temperate" distance from its star.
The discovery marks the first "transit" detection, where the dip in starlight caused by a planet orbiting in front of its star tips off astronomers to its existence.
"Our discovery proves that the transit-method is able to find also longer-period planets," says Spain's Hans Deeg of the Instituto de Astrofísica de Canarias in Tenerife, lead author of the report in the Nature journal. "The most exciting discoveries by transits are still to come."
First detected in 2008, the newly-reported planet, CoRot-9b, is about 0.84 times as heavy as Jupiter, and circles its star once every 95 days, meaning it experiences temperatures ranging from -10 to 314 degrees Fahrenheit, balmy by solar system standards. Several other worlds have been detected indirectly in such temperate orbits by measuring the gravitational wobbles they induce in their stars, but this is the first transit detection of one, says study co-author Didier Queloz of Switzerland's Observatoire de l'Universite´ de Geneve. That means CoRot-9b offers an opportunity to study its atmosphere by examination of the chemicals revealed in the spectra of its light.
"This one looks like another "warm Jupiter" on a relatively long period orbit," says planetary scientist Alan Boss of the Carnegie Institute of Washington (D.C.) "It is good to hear that CoRoT is still finding new transiting planets -- it has been a while since they have announced any new discoveries."
In theory, such a planet could have a moon with liquid water on its surface:
A moon could in principle be orbiting this planet; one can also calculate that is has to be on an orbit with a period shorter than 9 days. If such a moon would be very large (more than ~5 Earth radii), it should even have been detected in the current data; since this wasn't the case, we can exclude this. So, Titan-like moons are possible; though with surface temperatures that are much higher: the so-called effective temperature should be similar to the planet, (-20 to 150C, depending on the albedo) but real surface temperatures can be expected to be significantly higher due to Green-house effects; though a priori we can't exclude temperatures or conditions compatible with life on such a moon. "Sorry, I didn't see Avatar yet," Deeg adds. NASA's current Kepler space telescope mission, which will examine stars for transit planets out to about 3,000 light years away (one light year is about 5.9 trillion miles) in one direction of the Milky Way Galaxy, should yield many more planets resenbling CoRoT-9b, Deeg suggests, particularly given the positive results from the smaller CoRoT telescope.