4.7 Article

Liberating exomoons in white dwarf planetary systems

Journal

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 457, Issue 1, Pages 217-231

Publisher

OXFORD UNIV PRESS
DOI: 10.1093/mnras/stv2966

Keywords

methods: numerical; celestial mechanics; minor planets, asteroids: general; Moon; planets and satellites: dynamical evolution and stability; white dwarfs

Funding

  1. Royal Society [IE140641]
  2. NASA Origins of Solar Systems Program [NNX13A124G, NNX10AH40G, 1312645088477]
  3. BSF [2012384]
  4. European Union through ERC [320964]
  5. Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics
  6. NASA [NNX10AH40G, 133283] Funding Source: Federal RePORTER

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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 10(6) 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.

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