Tidal Heating of Exomoons in Resonance and Implications for Detection

Abstract: The habitability of exoplanets can be strongly influenced by the presence of an exomoon, and in some cases the exomoon itself could be a possible place for life to develop. For moons outside of the habitable zone, significant tidal heating may raise their surface temperature enough to be considered habitable. Tidal heating of a moon depends on numerous factors such as eccentricity, semimajor axis, size of parent planet, and presence of additional moons. In this work, we explore the degree of tidal heating possible for multi-moon systems in resonance using a combination of semi-analytic and numerical models. This demonstrates that even for a moon with zero initial eccentricity, when it moves into resonance with an outer moon, it can generate significant eccentricity and associated tidal heating. Depending on the mass ratio of the two moons, this resonance can either be short-lived ($\leq200$ Myr) or continue to be driven by the tidal migration of the moons. This tidal heating can also assist in making the exomoons easier to discover, and we explore two scenarios: secondary eclipses and outgassing of volcanic species. We then consider hypothetical moons orbiting known planetary systems to identify which will be beast suited for finding exomoons with these methods. We conclude with a discussion of current and future instrumentation and missions to better understand how practical it will be to make exomoon discoveries in these ways.