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Description
We report the discovery of CoRoT-8b, a dense small Saturn-class exoplanet that orbits a K1 dwarf in 6.2 days, and we derive its orbital parameters, mass, and radius. We analyzed two complementary data sets: the photometric transit curve of CoRoT-8b as measured by CoRoT and the radial velocity curve of CoRoT-8 as measured by the HARPS spectrometer. We find that CoRoT-8b is on a circular orbit with a semi-major axis of 0.063+/-0.001AU. It has a radius of 0.57+/-0.02RJ, a mass of 0.22+/-0.03MJ, and therefore a mean density 1.6+/-0.1g/cm^3^. With 67% of the size of Saturn and 72% of its mass, CoRoT-8b has a density comparable to that of Neptune (1.76g/cm^3^). We estimate its content in heavy elements to be 47-63 Earth masses, and the mass of its hydrogen-helium envelope to be 7-23 Earth masses. At 0.063AU, the thermal loss of hydrogen of CoRoT-8b should be no more than about 0.1% over an assumed integrated lifetime of 3Ga.
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