Infall of planetesimals onto growing giant planets: onset of runaway gas accretion and metallicity of their gas envelopes

Abstract

We have investigated the planetesimal accretion rate onto giant planets that are growing through gas accretion, using numerical simulations and analytical arguments. We derived the condition for gap opening in the planetesimal disk, which is determined by a competition between the expansion of the planet's Hill radius due to the planet growth and the damping of planetesimal eccentricity due to gas drag. We also derived the semi-analytical formula for the planetesimal accretion rate as a function of ratios of the rates of the Hill radius expansion, the damping, and planetesimal scattering by the planet. The predicted low planetesimal accretion rate due to gap opening in early gas accretion stages quantitatively shows that "phase 2," which is a long slow gas accretion phase before onset of runaway gas accretion, is not likely to occur. In late stages, rapid Hill radius expansion fills the gap, resulting in significant planetesimal accretion, which is as large as several $M_{\oplus }$ for Jupiter and Saturn. The efficient onset of runaway gas accretion and the late pollution may reconcile the ubiquity of extrasolar giant planets with metal-rich envelopes of Jupiter and Saturn inferred from interior structure models. These formulae will give deep insights into formation of extrasolar gas giants and the diversity in metallicity of transiting gas giants.

19 pages, 9 figures, accepted for publication in ApJ

References in corpus (4)

• Toward a Deterministic Model of Planetary Formation V. Accumulation Near the Ice Line
• On the Origin of HD149026b
• Planetesimal Accretion onto Growing Proto-Gas-Giant Planets
• Oligarchic planetesimal accretion and giant planet formation

Cited by in corpus (30)

• Separating gas-giant and ice-giant planets by halting pebble accretion
• Global Models of Planet Formation and Evolution
• Characterization of exoplanets from their formation III: The statistics of planetary luminosities
• Accretion and destruction of planetesimals in turbulent disks
• Grain opacity and the bulk composition of extrasolar planets. I. Results from scaling the ISM opacity
• The origin of the high metallicity of close-in giant exoplanets: Combined effect of the resonant and aerodynamic shepherding
• Breaking Degeneracies in Formation Histories by Measuring Refractory Content in Gas Giants
• Predicted diversity in water content of terrestrial exoplanets orbiting M dwarfs
• Jupiter's heavy-element enrichment expected from formation models
• Formation of moon systems around giant planets: Capture and ablation of planetesimals as foundation for a pebble accretion scenario
• Capture of Solids by Growing Proto-gas Giants: Effects of Gap Formation and Supply-limited Growth
• Planet Traps and Planetary Cores: Origins of the Planet-Metallicity Correlation
• Thermal torque effects on the migration of growing low-mass planets
• Exploring the conditions for forming cold gas giants through planetesimal accretion
• Dynamics and Accretion of Planetesimals
• Giant planet formation models with a self-consistent treatment of the heavy elements
• Setting the Stage: Planet formation and Volatile Delivery
• Embryo impacts and gas giant mergers II: Diversity of Hot Jupiters' internal structure
• The Bimodal Distribution in Exoplanet Radii: Considering Varying Core Compositions and ${\mathrm{H}}_2$ Envelope's Sizes
• Revising the Giant Planet Mass-Metallicity Relation: Deciphering the Formation Sequence of Giant Planets
• Enrichment of Jupiter's atmosphere by late planetesimal bombardment
• The origin of the high metallicity of close-in giant exoplanets II The nature of the sweet spot for accretion
• Formation of wide-orbit giant planets in protoplanetary disks with a decreasing pebble flux
• Super-Earths as Failed Cores in Orbital Migration Traps
• Orbital Circularization of a Planet Accreting Disk Gas: Formation of Distant Jupiters in Circular Orbits based on Core Accretion Model
• A low accretion efficiency of planetesimals formed at planetary gap edges
• Heavy-element Accretion by Proto-Jupiter in a Massive Planetesimal Disk, Revisited
• The Heavy-element Content Trend of Planets: A Tracer of their Formation Sites
• Solid Accretion onto Neptune-Mass Planets I: In-Situ Accretion and Constraints from the metallicity of Uranus and Neptune
• Detailed Calculations of the Efficiency of Planetesimal Accretion in the Core-Accretion Model -II: The effect of Saturn