Post-Capture Evolution of Potentially Habitable Exomoons

TL;DR

This paper models the dynamical evolution of potentially habitable exomoons captured by giant planets, showing many can settle into stable orbits and be detectable via transit variations.

Contribution

It provides the first detailed dynamical and observational analysis of captured terrestrial exomoons in habitable zones.

Findings

Approximately 50% of captured orbits become stable within a few million years.

Stable orbits are mostly low-inclination with no prograde/retrograde bias.

Detectable transit timing and duration variations for Earth-mass exomoons are predicted.

Abstract

The satellites of extrasolar planets (exomoons) have been recently proposed as astrobiological targets. Since giant planets in the habitable zone are thought to have migrated there, it is possible that they may have captured a former terrestrial planet or planetesimal. We therefore attempt to model the dynamical evolution of a terrestrial planet captured into orbit around a giant planet in the habitable zone of a star. We find that approximately half of loose elliptical orbits result in stable circular orbits over timescales of less than a few million years. We also find that those orbits are mostly low-inclination, but have no prograde/retrograde preference. In addition, we calculate the transit timing and duration variations for the resulting systems, and find that potentially habitable Earth-mass exomoons should be detectable.