A 1.9 Earth Radius Rocky Planet and the Discovery of a Non-Transiting Planet in the Kepler-20 System*

Lars A. Buchhave, Courtney D. Dressing, Xavier Dumusque, Ken Rice, Andrew Vanderburg, Annelies Mortier, Mercedes Lopez-Morales, Eric Lopez, Mia S. Lundkvist, Hans Kjeldsen, Laura Affer, Aldo S. Bonomo, David Charbonneau, Andrew Collier Cameron, Rosario Cosentino, Pedro Figueira, Aldo F. M. Fiorenzano, Avet Harutyunyan, Raphaëlle D. Haywood, John Asher JohnsonDavid W. Latham, Christophe Lovis, Luca Malavolta, Michel Mayor, Giusi Micela, Emilio Molinari, Fatemeh Motalebi, Valerio Nascimbeni, Francesco Pepe, David F. Phillips, Giampaolo Piotto, Don Pollacco, Didier Queloz, Dimitar Sasselov, Damien Ségransan, Alessandro Sozzetti, Stéphane Udry, Chris Watson

Research output: Contribution to journalArticlepeer-review


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 (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 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 (Mstar = 0.948 ± 0.051 M and Rstar = 0.964 ± 0.018 R). Kepler-20b is a 1.868-0.034+0.066 R planet in a 3.7 day period with a mass of 9.70-1.44+1.41 M, 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. 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+3.08 M and an orbital period of ~34 days in the gap between Kepler-20f (P ~ 11 days) and Kepler-20d (P ~ 78 days).
* Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofísica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.
Original languageEnglish
Article number160
Number of pages12
JournalAstronomical Journal
Issue number6
Early online date11 Nov 2016
Publication statusPublished - Dec 2016


  • planetary systems
  • planets and satellites: composition
  • stars: individual
  • techniques: radial velocities


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