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

Journal
Date Issued
2019
Author(s)
Rice, K.
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Mayo, A.
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Mortier, A.
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Buchhave, L. A.
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Vanderburg, A.
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Lopez-Morales, M.
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Zeng, L.
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Collier Cameron, A.
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Coffinet, A.
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Latham, D. W.
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Bouchy, F.
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Charbonneau, D.
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Dumusque, X.
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Figueira, P.
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Martinez Fiorenzano, A. F.
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Haywood, R. D.
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Johnson, J. Asher
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Lopez, E.
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Lovis, C.
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Mayor, M.
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Nava, C.
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Pepe, F.
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Phillips, D. F.
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Piotto, G.
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Sasselov, D.
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Ségransan, D.
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•
Udry, S.
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Watson, C.
DOI
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.
Volume
484
Issue
3
Start page
3731
Uri
Url
Issn Identifier
0035-8711
Ads BibCode
2019MNRAS.484.3731R
Rights
open.access
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