The fate of moons of close-in giant exoplanets

TL;DR

This paper investigates how the migration of close-in giant exoplanets affects their moons, concluding that most moons are ejected or collide with the planet during migration, making in situ formation unlikely.

Contribution

It demonstrates that planetary migration destabilizes moons, suggesting captured retrograde moons are more probable than in situ formed ones around close-in giants.

Findings

Moons become unstable during planetary migration.

Most moons are ejected or collide with the planet.

Captured retrograde moons are more likely than in situ formation.

Abstract

We show that the fate of moons of a close-in giant planet is mainly determined by the migration history of the planet in the protoplanetary disk. As the planet migrates in the disk from beyond the snow line towards a multi-day period orbit, the formed and forming moons become unstable as the planet's sphere of influence shrinks. Disk-driven migration is faster than the moons' tidal orbital evolution. Moons are eventually ejected from around close-in exoplanets or forced into collision with them before tides from the star affect their orbits. If moons are detected around close-in exoplanets, they are unlikely to have been formed in situ, instead they were captured from the protoplanetary disk on retrograde orbits around the planets.