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

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 $0.1-10\mathrm{au}$. Additionally, we determine the long-term evolution of the planets that had no runaway gas accretion phase after disc dispersal. We find: (i) Planets with $5{\mathrm{M}}_{\oplus }$ cores never undergo runaway accretion. The most massive envelope contained $2.8{\mathrm{M}}_{\oplus }$ with the planet orbiting at $10\mathrm{au}$. (ii) Accretion is more efficient onto $10{\mathrm{M}}_{\oplus }$ and $15{\mathrm{M}}_{\oplus }$ cores. For orbital radii $a_{\mathrm{p}}\ge 0.5\mathrm{au}$, $15{\mathrm{M}}_{\oplus }$ cores always experienced runaway gas accretion. For $a_{\mathrm{p}}\ge 5\mathrm{au}$, all but one of the $10{\mathrm{M}}_{\oplus }$ cores experienced runaway gas accretion. No planets experienced runaway growth at $a_{\mathrm{p}}=0.1\mathrm{au}$. (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 $\lesssim 15{\mathrm{M}}_{\oplus }$ at $\lesssim 0.1\mathrm{au}$ 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.

15 Pages, 9 Figures. Accepted for publication in MNRAS

References in corpus (9)

• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• Make Super-Earths, Not Jupiters: Accreting Nebular Gas onto Solid Cores at 0.1 AU and Beyond
• Formation of Jupiter using opacities based on detailed grain physics
• On the formation of planetary systems via oligarchic growth in thermally evolving viscous discs
• Ab initio equations of state for hydrogen (H-REOS.3) and helium (He-REOS.3) and their implications for the interior of Brown Dwarfs
• Global Models of Planet Formation and Evolution
• Minimum Core Masses for Giant Planet Formation With Realistic Equations of State and Opacities
• Occurrence and core-envelope structure of 1--4x Earth-size planets around Sun-like stars
• Grain opacity and the bulk composition of extrasolar planets. I. Results from scaling the ISM opacity

Cited by in corpus (20)

• The nature and origins of sub-Neptune size planets
• Hydrodynamics of embedded planets' first atmospheres - III. The role of radiation transport for super-Earth planets
• How planets grow by pebble accretion. III. Emergence of an interior composition gradient
• Radial-velocity discovery of a second planet in the TOI-1338/BEBOP-1 circumbinary system
• Pebbles versus planetesimals: the outcomes of population synthesis models
• Exploring the formation by core accretion and the luminosity evolution of directly imaged planets: The case of HIP 65426 b
• Planet formation via pebble accretion in externally photoevaporating discs
• Microlensing events indicate that super-Earth exoplanets are common in Jupiter-like orbits
• Formation of compact systems of super-Earths via dynamical instabilities and giant impacts
• The influence of infall on the properties of protoplanetary discs
• In situ formation of hot Jupiters with companion super-Earths
• From Dust to Planets I: Planetesimal and Embryo Formation
• Peter Pan Discs: finding Neverland's parameters
• TOI-1268b: the youngest, hot, Saturn-mass transiting exoplanet
• Global N-body simulations of circumbinary planet formation around Kepler-16 and -34 analogues I: Exploring the pebble accretion scenario
• Sub-Neptunes Are Drier Than They Seem: Rethinking the Origins of Water-Rich Worlds
• Combined Effects of Disk Winds and Turbulence-Driven Accretion on Planet Populations
• Circumplanetary Disk Candidate in the Disk of HD 163296 Traced by Localized Emission from Simple Organics
• Planet formation: key mechanisms and global models
• A Multi-Planet System's Sole Super-Puff: Exploring Allowable Physical Parameters for the Cold Super-Puff HIP 41378 f