A 1.9 Earth radius rocky planet and the discovery of a non-transiting planet in the Kepler-20 system
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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 publications in the literature (Rogers 2015; Weiss& Marcy 2014). Kepler-20b (Rp ∼ 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 Kepler-20 three of the planets in the Kepler-20 system 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+0.066 −0.034 R⊕ planet in a 3.7 day period with amass of 9.70+1.41 −1.44 M⊕ resulting in a mean density of 8.2 +1.5 −1.3 g cm−3 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+3.08 −3.61 M⊕ and an orbital period of ∼ 34 days in the gap between Kepler-20f (P ∼ 11 days) and Kepler-20d (P ∼78 days).
Buchhave , L A , Dressing , C D , Dumusque , X , Rice , K , Vanderburg , A , Mortier , A , Lopez-Morales , M , Lopez , E , Lundkvist , M S , Kjeldsen , H , Affer , L , Bonomo , A S , Charbonneau , D , Cameron , A C , Cosentino , R , Figueira , P , Fiorenzano , A F M , Harutyunyan , A , Haywood , R D , Johnson , J A , Latham , D W , Lovis , C , Malavolta , L , Mayor , M , Micela , G , Molinari , E , Motalebi , F , Nascimbeni , V , Pepe , F , Phillips , D F , Piotto , G , Pollacco , D , Queloz , D , Sasselov , D , Ségransan , D , Sozzetti , A , Udry , S & Watson , C 2016 , ' A 1.9 Earth radius rocky planet and the discovery of a non-transiting planet in the Kepler-20 system ' , Astronomical Journal , vol. 152 , no. 6 , 160 . https://doi.org/10.3847/0004-6256/152/6/160
© 2016, American Astronomical Society. This work is made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://dx.doi.org/10.3847/0004-6256/152/6/160