Posted: July 24, 2008
The discovery of a Jupiter-sized planet was announced earlier today at the international ‘Cool Stars, Stellar Systems and the Sun’ conference hosted by the University of St Andrews in Scotland.
The planet has been given the designation CoRoT-Exo-4b having been discovered using the CoRoT (Convection, Rotation and planetary Transits) space telescope led by the French space agency CNES. CoRoT uses the transit method to search for planets, by seeking out the tiny dips in a star’s brightness as a planet passes in front of it, temporarily blocking out some of its light.
Artist impression of CoRoT flying above the Earth. Image: CNES.
The newly discovered planet is slightly larger than our Sun and takes 9.2 days to orbit its host star. Although this may sound like an extremely short ‘year’, it is in fact one of the longest orbiting periods of any transiting planet found to date, with many ‘hot-Jupiters’ orbiting their parent stars in just a few hours.
Thanks to continuous coverage over several months, including follow up observations from a variety of ground based instruments on telescopes across the world (SOPHIE on the 180- centimetre telescope at the Observatoire de Haute Provence (France), HARPS on the 3.6-metre telescope at La Silla observatory (Chile) and UVES on the 8.2-metre Very Large Telescope at Paranal observatory (Chile), the 1-metre telescope at the Wise Observatory in Israel, the 1-metre Euler telescope at La Silla, and the 3.6-metre Canada-France-Hawaii telescope), the research team was also able to monitor variations in the host star's brightness between transits. And by tracking the motion of dark spots fixed on the star’s surface, its rotation period could be determined, revealing the surprising result that it is rotating at the same rate as its planet’s orbit. The astronomers presumed that the planet had insufficient mass and was located too distant from its star to have had much effect on its rotation, providing a reason for the theories of planet formation to be adapted yet again.
"We don’t know if CoRoT-Exo-4b and its star have always been rotating in synch since their formation about 1 billion years ago, or if the star became synchronized later,” says Dr Suzanne Aigrain from the University of Exeter, who led the analysis of the photometric data and spoke of the finding during the conference this morning. “CoRoT will no doubt find many more transiting planets, and by systematically measuring their host stars' rotation periods we will gain valuable insight into how stars interact with their planets."
CoRoT, which was launched at the end of 2006, is the first space-based mission dedicated to searching for extrasolar planets and has now harvested six new exoplanets. Most of these are gas giants, but one puzzling object has a mass that places it between that of a planet and a brown dwarf. Furthermore, CoRoT has found a tiny signal in its observations that, if caused by a transit, could be due to a planet just 1.7 times the radius of the Earth. The CoRoT planet-hunter will certainly be the one to watch in the coming months.