Resonant Removal of Exomoons During Planetary Migration

TL;DR

This paper demonstrates that inward migration of giant exoplanets can lead to the destruction of their moons via a resonance mechanism, implying exomoon presence could reveal planetary migration histories.

Contribution

It introduces a dynamical mechanism, the evection resonance, explaining how migrating planets can naturally lose their moons, a novel insight into exomoon survival.

Findings

Moons within about 10 planetary radii are vulnerable to destruction.

The likelihood of moon loss depends on planetary mass, oblateness, and initial formation location.

Exomoon observations could inform us about planetary migration processes.

Abstract

Jupiter and Saturn play host to an impressive array of satellites, making it reasonable to suspect that similar systems of moons might exist around giant extrasolar planets. Furthermore, a significant population of such planets is known to reside at distances of several Astronomical Units (AU), leading to speculation that some moons thereof might support liquid water on their surfaces. However, giant planets are thought to undergo inward migration within their natal protoplanetary disks, suggesting that gas giants currently occupying their host star's habitable zone formed further out. Here we show that when a moon-hosting planet undergoes inward migration, dynamical interactions may naturally destroy the moon through capture into a so-called "evection resonance." Within this resonance, the lunar orbit's eccentricity grows until the moon eventually collides with the planet. Our work suggests that moons orbiting within about 10 planetary radii are susceptible to this mechanism, with the exact number dependent upon the planetary mass, oblateness and physical size. Whether moons survive or not is critically related to where the planet began its inward migration as well as the character of inter-lunar perturbations. For example, a Jupiter-like planet currently residing at 1AU could lose moons if it formed beyond 5AU. Cumulatively, we suggest that an observational census of exomoons could potentially inform us on the extent of inward planetary migration, for which no reliable observational proxy currently exists.