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Masses and radii for the three super-Earths orbiting GJ 9827, and implications for the composition of small exoplanets

Research output: Contribution to journalArticle

  • L. Malavolta
  • A. Mayo
  • A. Mortier
  • L. A. Buchhave
  • L. Affer
  • A. Vanderburg
  • M. Lopez-Morales
  • E. Poretti
  • L. Zeng
  • A. C. Cameron
  • M. Damasso
  • A. Coffinet
  • D. W. Latham
  • A. S. Bonomo
  • F. Bouchy
  • D. Charbonneau
  • X. Dumusque
  • P. Figueira
  • A. F. Martinez Fiorenzano
  • R. D. Haywood
  • J. Asher Johnson
  • E. Lopez
  • C. Lovis
  • M. Mayor
  • G. Micela
  • E. Molinari
  • V. Nascimbeni
  • C. Nava
  • F. Pepe
  • D. F. Phillips
  • G. Piotto
  • D. Sasselov
  • D. Ségransan
  • A. Sozzetti
  • S. Udry
  • C. Watson

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Original languageEnglish
Pages (from-to)3731–3745
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Publication statusPublished - 12 Jan 2019


Super-Earths belong to a class of planet not found in the Solar System, but which appear common in the Galaxy. Given that some super-Earths are rocky, while others retain substantial atmospheres, their study can provide clues as to the formation of both rocky planets and gaseous planets, and - in particular - they can help to constrain the role of photo-evaporation in sculpting the exoplanet population. GJ 9827 is a system already known to host 3 super-Earths with orbital periods of 1.2, 3.6 and 6.2 days. Here we use new HARPS-N radial velocity measurements, together with previously published radial velocities, to better constrain the properties of the GJ 9827 planets. Our analysis can't place a strong constraint on the mass of GJ 9827 c, but does indicate that GJ 9827 b is rocky with a composition that is probably similar to that of the Earth, while GJ 9827 d almost certainly retains a volatile envelope. Therefore, GJ 9827 hosts planets on either side of the radius gap that appears to divide super-Earths into pre-dominantly rocky ones that have radii below $\sim 1.5 R_\oplus$, and ones that still retain a substantial atmosphere and/or volatile components, and have radii above $\sim 2 R_\oplus$. That the less heavily irradiated of the 3 planets still retains an atmosphere, may indicate that photoevaporation has played a key role in the evolution of the planets in this system.

    Research areas

  • astro-ph.EP, astro-ph.SR

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