Planetesimal Accretion onto Growing Proto-Gas-Giant Planets

TL;DR

This paper investigates how planetesimal dynamics influence gas accretion onto proto-gas-giant cores, potentially explaining the diversity in their internal structures and metallicities observed in the solar system and exoplanets.

Contribution

It introduces a new mechanism where resonance trapping and subsequent destabilization of planetesimals affect gas accretion and core composition in giant planet formation.

Findings

Planetesimals cannot easily pass through core resonances, reducing bombardment during early growth.

Resonance overlap causes dynamical instability and increased eccentricity of planetesimals.

Gas drag induces planetesimal migration and collision, leading to a surge in bombardment during later stages.

Abstract

The solar and extra solar gas giants appear to have diverse internal structure and metallicities. We examine a potential cause for these dispersions in the context of the conventional sequential accretion formation scenario. In principle, gas accretion onto cores with masses below several times that of the Earth is suppressed by the energy released from the bombardment of residual planetesimals. We show that these planetesimals generally cannot pass through the mean motion resonances of the cores, and the suppression of planetesimal bombardment rate enables the cores to accrete gas with little interruption. During growth from the cores to protoplanets, as the resonances overlap with each other, the trapped planetesimals become dynamically unstable and their eccentricity excitation is strongly enhanced. Subsequent gas drag induces the planetesimals to migrate and collide with the protoplanet. This process leads to the resumption and a surge of planetesimal bombardment during the advanced stage of the protoplanet growth. This mechanism may account for the diversity of the core-envelope structure between Jupiter, Saturn and the metallicity dispersion inferred from the transiting extra solar planets.