The Corot satellite strikes again with another fascinating planet discovery. This time, the newly discovered gas giant planet may have an interior that closely resembles those of Jupiter and Saturn in our own Solar System.
Very few planets are temperate enough to allow the presence of liquid water, but the newly discovered Corot-9b is one of them. It was found on 16 May 2008 and orbits its star every 95.274 days, a little longer than Mercury takes to go round the Sun.
More than 400 exoplanets have been discovered so far and 70 of them have been found by the ‘transit’ method. A transit is a kind of eclipse and occurs when a celestial body passes in front of its host star and blocks some but not all of the star’s light. This temporarily dims the apparent brightness of the star and enables the planet’s mass, diameter, density and temperature to be deduced. The time between similar transits gives the orbital period of the planet.
Corot-9b is the first transiting planet to have both a longer period and a near-circular orbit. Its orbit is slightly elliptical but at closest approach to its parent star it reaches a distance of 54 million kilometres. Although that is only about the distance of Mercury in our Solar System, it is by far the largest orbit of any transiting planet found so far. Because it orbits a star cooler than our Sun, calculations estimate that Corot-9b’s temperature could lie somewhere between –23°C and 157°C. Corot-9b has a radius around 1.05 times that of Jupiter but only 84% of the mass. This leads to a density of 0.90 g/cc, or 68% that of Jupiter. “Corot-9b is the first exoplanet that is definitely similar to a planet in our Solar System,” says Hans Deeg, a researcher at the Instituto de Astrofísica de Canarias, whose paper on the discovery is published today in Nature.