KOI-152's Low Density Planets

Abstract: KOI-152 is among the first known systems of multiple transiting planetary candidates (Steffen et al. 2010) ranging in size from 3.5 to 7 times the size of the Earth, in a compact configuration with orbital periods near a 1:2:4:6 chain of commensurability, from 13.5 days to 81.1 days. All four planets exhibit transit timing variations with periods that are consistent with the distance of each planet to resonance with its neighbors. We perform a dynamical analysis of the system based on transit timing measurements over 1282 days of \textit{Kepler} photometry. Stellar parameters are obtained with a combination of spectral classification and the stellar density constraints provided by light curve analysis and orbital eccentricity solutions from our dynamical study. Our models provide tight constraints on the masses of all four transiting bodies, demonstrating that they are planets and that they orbit the same star. All four of KOI-152's transiting planets have low densities given their sizes, consistent with other studies of compact multiplanet transiting systems. The largest of the four, KOI-152.01, has the lowest bulk density yet determined amongst sub-Saturn mass planets.