KEPLER-7b: A TRANSITING PLANET WITH UNUSUALLY LOW DENSITY

We report on the discovery and confirmation of Kepler-7b, a transiting planet with unusually low density. The mass is less than half that of Jupiter, M P = 0.43 M J , but the radius is 50% larger, R P = 1.48 R J . The resulting density, ρ P = 0.17 g cm −3 , is the second lowest reported so far for an extrasolar planet. The orbital period is fairly long, P = 4.886 days, and the host star is not much hotter than the Sun, T eff = 6000 K. However, it is more massive and considerably larger than the Sun, M ⋆ = 1.35 M ☉ and R ⋆ = 1.84 R ☉ , and must be near the end of its life on the main sequence.