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 = 4.886days, and the host star is not much hotter than the Sun, T _eff = 6000K. 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.