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

K. Rice, 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
(Submitted on 18 Dec 2018)

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 ∼1.5R⊕, and ones that still retain a substantial atmosphere and/or volatile components, and have radii above ∼2R⊕. 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.

Comments:    16 pages, 9 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society
Subjects:    Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as:    arXiv:1812.07302 [astro-ph.EP] (or arXiv:1812.07302v1 [astro-ph.EP] for this version)
Submission history
From: W. K. M. Rice
[v1] Tue, 18 Dec 2018 11:18:16 UTC (2,379 KB)
https://arxiv.org/abs/1812.07302