  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.
