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, Stephane Udry, Laura Affer, Aldo S. Bonomo, Lars A. Buchhave, Rosario Cosentino, Pedro Figueira, Aldo F. M. Fiorenzano, Avet Harutyunyan, Raphaelle 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 Segransan, Alessandro Sozzetti, Andrew Szentgyorgyi, Chris Watson

*Corresponding author for this work

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Kepler-93b is a 1.478 ± 0.019 R planet with a 4.7 day period around a bright (V = 10.2), astroseismically characterized 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 obtained with the HARPS-N  spectrograph on the Telescopio Nazionale Galileo and 32 archival Keck/HIRES observations, we present a precise mass estimate of 4.02 ± 0.68 M . The corresponding high density of 6.88 ± 1.18 g cm–3 is consistent with a rocky composition of primarily iron and magnesium silicate. We compare Kepler-93b to other dense planets with well-constrained parameters and find that between 1 and 6 M , all dense planets including the Earth and Venus are well-described by the same fixed ratio of iron to magnesium silicate. There are as of yet no examples of such planets with masses >6 M . All known planets in this mass regime have lower densities requiring significant fractions of volatiles or H/He gas. We also constrain the mass and period of the outer companion in the Kepler-93 system from the long-term radial velocity trend and archival adaptive optics images. As the sample of dense planets with well-constrained masses and radii continues to grow, we will be able to test whether the fixed compositional model found for the seven dense planets considered in this paper extends to the full population of 1-6 M planets.

Original languageEnglish
Article number135
Number of pages7
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 20 Feb 2015


  • Planetary systems
  • Planets and satellites: composition
  • Stars: individual (Kepler-93=KOI 69=KIC 3544595)
  • Techniques: radial velocities
  • 100 Earth masses
  • Super-Earths
  • Radius relationships
  • Extrasolar planets
  • Solar-systems
  • Stars
  • Abundances
  • Transits
  • Catalog
  • Orbits


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