Masses and radii for the three super-Earths orbiting GJ 9827, and implications for the composition of small exoplanets
Abstract
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 and gaseous planets, and - in particular - they can help to constrain the role of photoevaporation in sculpting the exoplanet population. GJ 9827 is a system already known to host three super-Earths with orbital periods of 1.2, 3.6, and 6.2 d. 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 cannot 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 three planets still retains an atmosphere, may indicate that photoevaporation has played a key role in the evolution of the planets in this system.
Citation
Rice , K , Malavolta , L , Mayo , A , Mortier , A , Buchhave , L A , Affer , L , Vanderburg , A , Lopez-Morales , M , Poretti , E , Zeng , L , Cameron , A C , Damasso , M , Coffinet , A , Latham , D W , Bonomo , A S , Bouchy , F , Charbonneau , D , Dumusque , X , Figueira , P , Martinez Fiorenzano , A F , Haywood , R D , Johnson , J A , Lopez , E , Lovis , C , Mayor , M , Micela , G , Molinari , E , Nascimbeni , V , Nava , C , Pepe , F , Phillips , D F , Piotto , G , Sasselov , D , Ségransan , D , Sozzetti , A , Udry , S & Watson , C 2019 , ' Masses and radii for the three super-Earths orbiting GJ 9827, and implications for the composition of small exoplanets ' , Monthly Notices of the Royal Astronomical Society , vol. 484 , no. 3 , pp. 3731-3745 . https://doi.org/10.1093/mnras/stz130
Publication
Monthly Notices of the Royal Astronomical Society
Status
Peer reviewed
ISSN
0035-8711Type
Journal article
Description
Funding: UK STFC consolidated grant number ST/M001296/1 (ACC).Collections
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