Fate of a remnant solid disk around an eccentric giant planet

TL;DR

This study investigates the likelihood and extent of solid material accretion onto eccentric giant planets after protoplanetary disk dissipation, using simulations and analytical models to understand their heavy-element enrichment.

Contribution

It introduces a new analytical model and simulation results showing limited solid accretion onto eccentric giants post-disk, highlighting the importance of orbital dynamics in planetary composition.

Findings

Most solids are ejected or fall into the star, not accreted.

Eccentricity increases solid accretion, inclination decreases it.

Eccentric giants in outer disks accrete about 0.01-0.1 Earth masses of solids.

Abstract

The composition of giant planets' atmospheres is an important tracer of their formation history. While many theoretical studies investigate the heavy-element accretion within a gaseous protoplanetary disk, the possibility of solid accretion after disk dissipation has not been explored. Here, we focus on the case of a gas giant planet excited to an eccentric orbit and assess the likelihood of solid accretion after disk dissipation. We perform N-body simulations of planetesimals and embryos around an eccentric giant planet. We consider various sizes and orbits for the eccentric planet and determine the fate of planetesimals and embryos. We find that the orbital evolution of solids, such as planetesimals and embryos, is regulated by weak encounters with the eccentric planet rather than strong close encounters. Even in the region where the Safronov number is smaller than unity, most solid materials fall onto the central star or are ejected from the planetary system. We also develop an analytical model of the solid accretion along the orbital evolution of a giant planet, where the accretion probability is obtained as a function of the planetary mass, radius, semi-major axis, eccentricity, inclination, and solid disk thickness. Our model predicts that $\sim$0.01-0.1 $M_\oplus$ of solids is accreted onto an eccentric planet orbiting in the outer disk ($\sim10$ au). The accreted heavy-element mass increases (decreases) with the eccentricity (inclination) of the planet. We also discuss the possibility of collisions of terrestrial planets and find that $\sim10\%$ of the hot Jupiters formed via high-eccentric migration collide with a planet of $10M_\oplus$. However, we find that solid accretion and collisions with terrestrial planets are minor events for planets in the inner orbit, and a different accretion process is required to enrich eccentric giant planets with heavy elements.