HARPS-N radial velocities of KOI-70

A transition from rocky to gaseous planets with a planetary transition radius of ~1.6R_{Earth}_ has recently been proposed by several articles in the literature. Kepler-20b (R_p_~1.9R_{Earth}_) has a size beyond this transition radius; however, previous mass measurements were not sufficiently precise to allow definite conclusions to be drawn regarding its composition.

We present new mass measurements of three of the planets in the Kepler-20 system that are facilitated by 104 radial velocity measurements from the HARPS-N spectrograph and 30 archival Keck/HIRES observations, as well as an updated photometric analysis of the Kepler data and an asteroseismic analysis of the host star (M_*_=0.948+/-0.051M_{Sun}_ and R_*_=0.964+/-0.018R_{Sun}_). Kepler-20b is a 1.868_-0.034_^+0.066^R_{Earth}_ planet in a 3.7day period with a mass of 9.70_-1.44_^+1.41^M_{Earth}_, resulting in a mean density of 8.2_-1.3_^+1.5^g/cm^3^, indicating a rocky composition with an iron-to-silicate ratio consistent with that of the Earth.