WASP-29b: A sub-Saturn transiting exoplanet

We report the discovery of a Saturn-mass planet transiting a V = 11.3 K4 dwarf star every 3.9 d. WASP-29b has a mass of 0.25 M_Jup and a radius of 0.7–0.8 R_Jup , making it most similar to the well-studied planet HD 149026b. On a mass–radius plot WASP-29b now marks the lower-left boundary of the known Saturn- and Jupiter-like planets. WASP-29b  appears to have an above-Solar metallicity and fits a previous suggestion that the density of Saturn-mass planets is correlated with their metallicity. We suggest that WASP-29b has a larger core than the less-dense, Saturn-like planet HAT-P-12b.