The Mass of Kepler-93b and The Composition of Terrestrial Planets

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

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Kepler-93b is a 1.478 ± 0.019 R ⊕ planet with a4.7 day period around a bright (V = 10.2), astroseismicallycharacterized host star with a mass of 0.911 ± 0.033 M⊙ and a radius of 0.919 ± 0.011 R⊙. Based on 86 radial velocity observations obtainedwith the HARPS-N spectrograph on the Telescopio Nazionale Galileo and 32archival Keck/HIRES observations, we present a precise mass estimate of4.02 ± 0.68 M ⊕. The corresponding high densityof 6.88 ± 1.18 g cm-3 is consistent with a rockycomposition of primarily iron and magnesium silicate. We compareKepler-93b to other dense planets with well-constrained parameters andfind that between 1 and 6 M ⊕, all dense planetsincluding the Earth and Venus are well-described by the same fixed ratioof iron to magnesium silicate. There are as of yet no examples of suchplanets with masses >6 M ⊕. All known planets inthis mass regime have lower densities requiring significant fractions ofvolatiles or H/He gas. We also constrain the mass and period of theouter companion in the Kepler-93 system from the long-term radialvelocity trend and archival adaptive optics images. As the sample ofdense planets with well-constrained masses and radii continues to grow,we will be able to test whether the fixed compositional model found forthe seven dense planets considered in this paper extends to the fullpopulation of 1-6 M ⊕ planets.Based on observations made with the Italian Telescopio Nazionale Galileo(TNG) operated on the island of La Palma by the Fundación GalileoGalilei of the INAF (Istituto Nazionale di Astrofisica) at the SpanishObservatorio del Roque de los Muchachos of the Instituto de Astrofisicade Canarias.
Original languageEnglish
Pages (from-to)135
JournalThe Astrophysical Journal
Issue number2
Publication statusPublished - 20 Feb 2015


  • Planetary systems
  • planets and satellites: composition
  • stars: individual: Kepler-10 KOI-072 KIC 11904151
  • techniques: radial velocities

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