Kepler-20 is a solar-type star (V = 12.5) hosting a compact system of five transiting planets, all packed within the orbital distance of Mercury in our own solar system. A transition from rocky to gaseous planets with a planetary transition radius of ∼1.6 R⊕ has recently been proposed by several articles in the literature. Kepler-20b (∼ 1.9 R⊕) 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 ± 0.051 M⊙and = R∗ = 0.964 ± 0.018 R⊙). Kepler-20b is a 1.868-0.034+0.006 planet in a 3.7 day period with a mass of 9.70-1.44+1.41M⊕, resulting in a mean density of 8.2-1.3+1.5, indicating a rocky composition with an iron-to-silicate ratio consistent with that of the Earth. This makes Kepler-20b the most massive planet with a rocky composition found to date. Furthermore, we report the discovery of an additional non-transiting planet with a minimum mass of 19.96-3.61+3.08M⊕ and an orbital period of ∼34 days in the gap between Kepler-20f (P ∼ 11 days) and Kepler-20d (P ∼ 78 days).
- planetary systems
- planets and satellites: composition
- stars: individual
- techniques: radial velocities
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science