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, rho(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(star) = 1.35 M(circle dot) and R(star) = 1.84R(circle dot), and must be near the end of its life on the main sequence.