  Many potential mechanisms for delivering planetary debris to within a few
Roche radii of white dwarfs rely on gravitational scattering events that
feature perturbers which are giant planets or terrestrial planets. However, the
population of these planets orbiting white dwarfs is still unknown, and for a
substantial fraction of white dwarfs the largest planetary survivors of stellar
evolution may be sub-terrestrial mass minor planets. Here, we attempt to
identify the smallest mass perturbers that could pollute white dwarfs. Through
computationally expensive numerical simulations of both unstable and stable
configurations of minor planets, we find that this critical lower bound equals
approximately one Luna mass. Further, we find that as this mass limit is
approached from above, the typical cooling age at which white dwarf pollution
occurs increases. Consequently, there is a two order-of-magnitude range of
perturber masses between Earth and its moon that has remained largely
unexplored in white dwarf pollution studies, despite the potential formation of
thousands of such Luna-sized objects in these systems.
