  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 years. The short sinking
timescale for the pollutants indicate 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 among planets in WD systems easily triggers moon ejection. Repeated
close encounters within tenths of a 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 pericenters with respect to the WD of only a fraction of an AU,
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.
