Innocent Bystanders: Orbital Dynamics of Exomoons during Planet-Planet Scattering

Abstract

Planet-planet scattering is the leading mechanism to explain the broad eccentricity distribution of observed giant exoplanets. Here we study the orbital stability of primordial giant planet moons in this scenario. We use N-body simulations including realistic oblateness and evolving spin evolution for the giant planets. We find that the vast majority (80-90% across all our simulations) of orbital parameter space for moons is destabilized. There is a strong radial dependence, as moons past 0.1 Hill radii are systematically removed. Closer-in moons on Galilean-moon-like orbits (< 0.04 Hill radii) have a good ( 20-40%) chance of survival. Destabilized moons may undergo a collision with the star or a planet, be ejected from the system, be captured by another planet, be ejected but still orbiting its free-floating host planet, or survive on heliocentric orbits as "planets." The survival rate of moons increases with the host planet mass but is independent of the planet's final (post-scattering) orbits. Based on our simulations we predict the existence of an abundant galactic population of free- floating (former) moons.

15 pages, 9 figures, 1 table, accepted for publication in ApJ

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• On the Detection of Exomoons Transiting Isolated Planetary-Mass Objects
• Can close-in giant exoplanets preserve detectable moons?
• Presence of water on exomoons orbiting free-floating planets: a case study
• Microlensing due to free-floating moon-planet systems
• Dynamics of the clumps partially disrupted from a planet around a neutron star
• Capture of satellites during planetary encounters A case study of the Neptunian moons Triton and Nereid
• New Dynamical State and Habitability of the HD 45364 Planetary System