Liberating exomoons in white dwarf planetary systems

Previous studies indicate that more than a quarter of all white dwarf (WD) atmospheres are polluted by remnant planetary material, with some WDs being observed to accrete the mass of Pluto in 106 yr. The short sinking time-scale for the pollutants indicates that the material must be frequently reple...

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Bibliographic Details
Published in:Monthly notices of the Royal Astronomical Society 2016-03, Vol.457 (1), p.217-231
Main Authors: Payne, Matthew J., Veras, Dimitri, Holman, Matthew J., Gänsicke, Boris T.
Format: Article
Language:English
Subjects:
Air pollution
Astronomy
Dynamical systems
Dynamics
Moons
Orbits
Planetary evolution
Planetary systems
Planets
Scattering
White dwarf stars
White dwarfs
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Summary:Previous studies indicate that more than a quarter of all white dwarf (WD) atmospheres are polluted by remnant planetary material, with some WDs being observed to accrete the mass of Pluto in 106 yr. The short sinking time-scale for the pollutants indicates that the material must be frequently replenished. Moons may contribute decisively to this pollution process if they are liberated from their parent planets during the post-main-sequence evolution of the planetary systems. Here, we demonstrate that gravitational scattering events amongst planets in WD systems easily trigger moon ejection. Repeated close encounters within tenths of planetary Hill radii are highly destructive to even the most massive, close-in moons. Consequently, scattering increases both the frequency of perturbing agents in WD systems, as well as the available mass of polluting material in those systems, thereby enhancing opportunities for collision and fragmentation and providing more dynamical pathways for smaller bodies to reach the WD. Moreover, during intense scattering, planets themselves have pericentres with respect to the WD of only a fraction of an astronomical unit, causing extreme Hill-sphere contraction, and the liberation of moons into WD-grazing orbits. Many of our results are directly applicable to exomoons orbiting planets around main-sequence stars.
ISSN:0035-8711
1365-2966
DOI:10.1093/mnras/stv2966