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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.
Original language | English |
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Pages (from-to) | 3731-3745 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 484 |
Issue number | 3 |
Early online date | 12 Jan 2019 |
DOIs | |
Publication status | Published - 11 Apr 2019 |
Keywords
- 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)
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Astronomy at St Andrews 2015-2018: Astronomy at St Andrews 2015-2018
Jardine, M. M. (PI), Cameron, A. C. (CoI), Cyganowski, C. J. (CoI), Horne, K. D. (CoI) & Wood, K. (CoI)
Science & Technology Facilities Council
1/04/15 → 31/03/18
Project: Standard