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In situ accretion of gaseous envelopes on to planetary cores embedded in evolving protoplanetary discs

Accepted version
Peer-reviewed

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Authors

Coleman, Gavin AL 
Papaloizou, John CB 
Nelson, Richard P 

Abstract

The core accretion hypothesis posits that planets with significant gaseous envelopes accreted them from their protoplanetary discs after the formation of rocky/icy cores. Observations indicate that such exoplanets exist at a broad range of orbital radii, but it is not known whether they accreted their envelopes in situ, or originated elsewhere and migrated to their current locations. We consider the evolution of solid cores embedded in evolving viscous discs that undergo gaseous envelope accretion in situ with orbital radii in the range 0.1–10 au. Additionally, we determine the long-term evolution of the planets that had no runaway gas accretion phase after disc dispersal. We find the following. (i) Planets with 5 M⊕ cores never undergo runaway accretion. The most massive envelope contained 2.8 M⊕ with the planet orbiting at 10 au. (ii) Accretion is more efficient on to 10 M⊕ and 15 M⊕ cores. For orbital radii ap ≥ 0.5 au, 15 M⊕ cores always experienced runaway gas accretion. For ap ≥ 5 au, all but one of the 10 M⊕ cores experienced runaway gas accretion. No planets experienced runaway growth at ap = 0.1 au. (iii) We find that, after disc dispersal, planets with significant gaseous envelopes cool and contract on Gyr time-scales, the contraction time being sensitive to the opacity assumed. Our results indicate that Hot Jupiters with core masses ≲15 M⊕ at ≲0.1 au likely accreted their gaseous envelopes at larger distances and migrated inwards. Consistently with the known exoplanet population, super-Earths and mini-Neptunes at small radii during the disc lifetime, accrete only modest gaseous envelopes.

Description

Keywords

planets and satellites: atmospheres, planets and satellites: formation, planetdisc interactions, protoplanetary discs

Journal Title

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

Conference Name

Journal ISSN

0035-8711
1365-2966

Volume Title

470

Publisher

Oxford University Press
Sponsorship
The simulations presented in this paper utilized Queen Mary's MidPlus computational facilities, supported by QMUL Research-IT and funded by EPSRC grant EP/K000128/1. This research was supported in part by the National Science Foundation under Grant No. NSF PHY-1125915. We acknowledge the referee, Kaitlin Kratter, whose comments helped to improve this paper.