Lunar collision rate with primordial black holes

A recent letter studied cratering during collisions between rocky bodies and primordial black holes. Hydrodynamic simulations in that work showed that ejecta blankets from these collisions are steeper because the black holes completely penetrate the target, potentially making these craters distinguishable from traditional point-like impactors. This may allow us to use lunar craters to constrain primordial black holes in the asteroid-mass window, about 10(17)-10(19) g. In this work, we calculate the lunar dark matter flux from the Galactic halo and several models for a dark disc. We consider several effects that may enhance the dark matter flux, such as gravitational focusing on the Solar system and historical modulations due to the Solar system's galactic orbit. We find that non-detection of novel craters on the Moon can constrain relativistic compact MACHO dark matter up to 10(17) g at 95 per cent confidence, motivating a detailed search through lunar surface scans. In addition, we show that fluxes near Earth from dark discs may be significantly enhanced by gravitational focusing and that the relative velocity between the disc and the Sun can result in annual modulations out of phase with the annual modulations from the halo.