Masses and radii for the three super-Earths orbiting GJ 9827, and implications for the composition of small exoplanets. Issue 3 (12th January 2019)

• Record Type: Journal Article
• Authors: 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 Asher; 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;
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 484:Issue 3(2019)
• Page Start: 3731
• Page End: 3745
• Publication Date: 2019-01-12
• Subjects: techniques: radial velocities -- planets and satellites: composition -- planets and satellites: detection -- planets and satellites: fundamental parameters -- planets and satellites: general -- Stars: individual: GJ 9827 (2MASS J23270480−0117108, EPIC 246389858, HIP 115752); Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stz130
• Languages: English
• ISSNs: 0035-8711

Abstract

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