Capture of planetesimals by waning circumplanetary gas disks

TL;DR

This study investigates how planetesimals are captured and evolve in waning circumplanetary gas disks, revealing conditions that allow long-term survival and implications for irregular satellite formation.

Contribution

It provides new insights into the capture process of planetesimals during disk dispersal, highlighting the effects of gas drag strength and dispersal timescale on orbital outcomes.

Findings

Captured planetesimals can survive long-term in weak gas drag conditions.

Their semi-major axes are typically less than one-third of the planet's Hill radius.

Final orbital eccentricities and inclinations are generally large, influenced by initial gas drag and dispersal timing.

Abstract

When gas giant protoplanets grow sufficiently massive, circumplanetary disks would form. While solid bodies captured by the circumplanetary disks likely contribute to the growth of the planets and regular satellites around them, some of captured bodies would remain in planet-centered orbits after the dispersal of the disk. We examine capture and subsequent orbital evolution of planetesimals in waning circumplanetary gas disks using three-body orbital integration. We find that some of captured planetesimals can survive in the circumplanetary disk for a long period of time under such weak gas drag. Captured planetesimals have semi-major axes smaller than about one third of the planet's Hill radius. Distributions of their eccentricities and inclinations after disk dispersal depend on the strength of gas drag and the timescale of disk dispersal, and initially strong gas drag and quick disk dispersal facilitates capture and survival of planetesimals. However, in such a case, final orbital eccentricities and inclinations of captured bodies remain rather large. Although our results suggest that some of the present irregular satellites of gas giant planets with small semi-major axes would have been captured by gas drag, other mechanisms are required to fully explain their current orbital characteristics.