Survivability of Moon Systems Around Ejected Gas Giants

TL;DR

This study investigates the survivability and orbital characteristics of moons around gas giants ejected from planetary systems, revealing that many moons can survive, maintain resonances, and potentially support life even in rogue planet scenarios.

Contribution

It provides the first detailed numerical analysis of moon survival, orbital dynamics, and resonance stability during planetary ejection events.

Findings

Moons can survive beyond 200 planetary radii from their host planet.

Surviving moons exhibit a wide range of inclinations and eccentricities, including retrograde orbits.

Many moons in mean-motion resonances remain stable after planetary ejection.

Abstract

We examine the effects that planetary encounters have on the moon systems of ejected gas giant planets. We conduct a suite of numerical simulations of planetary systems containing three Jupiter-mass planets (with the innermost planet at 3 AU) up to the point where a planet is ejected from the system. The ejected planet has an initial system of 100 test-particle moons. We determine the survival probability of moons at different distances from their host planet, measure the final distribution of orbital elements, examine the stability of resonant configurations, and characterize the properties of moons that are stripped from the planets. We find that moons are likely to survive in orbits with semi-major axes out beyond 200 planetary radii (0.1 AU in our case). The orbital inclinations and eccentricities of the surviving moons are broadly distributed and include nearly hyperbolic orbits and retrograde orbits. We find that a large fraction of moons in two-body and three-body mean-motion resonances also survive planetary ejection with the resonance intact. The moon-planet interactions, especially in the presence of mean-motion resonance, can keep the interior of the moons molten for billions of years via tidal flexing, as is seen in the moons of the gas giant planets in the solar system. Given the possibility that life may exist in the subsurface ocean of the Galilean satellite Europa, these results have implications for life on the moons of rogue planets---planets that drift through the galaxy with no host star.