CAPTURE OF PLANETESIMALS BY WANING CIRCUMPLANETARY GAS DISKS

Abstract

ABSTRACT Circumplanetary disks will form when gas-giant protoplanets grow sufficiently massive. While solid bodies captured by the circumplanetary disks likely contribute to the growth of the planets and regular satellites around them, some of the captured bodies will remain in planet-centered orbits after the dispersal of the disk. We examine the capture and subsequent orbital evolution of planetesimals in waning circumplanetary gas disks using three-body orbital integration. We find that some of the captured planetesimals can survive in the circumplanetary disk for a long period of time under such weak gas drag. Captured planetesimals have semimajor axes smaller than about one-third of the planet's Hill radius. The 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 facilitate capture and survival of planetesimals. However, in such cases, the 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 semimajor axes would have been captured by gas drag, other mechanisms are required to fully explain their current orbital characteristics.