Segregation on small rubble bodies due to impact-induced seismic shaking

We present a framework to study regolith segregation on rubble-pile asteroids—self-gravitating granular aggregates—due to seismic shaking induced by impacts sustained during their lifetimes. We first relate the amplitude and frequency of surface vibrations to the location and severity of an impact, and the rubble body’s geometry and bulk properties. For illustration, the body is taken to be an ellipsoid with size and spin close to that of Itokawa, although more complex asteroid shapes may be incorporated. We then model the body’s collisional history stochastically given the variability in the impact activity on an asteroid. Finally, we use discrete element simulations to investigate the regolith’s response to impacts. In these simulations, in any sample collisional history, every time an impact occurs, a bin filled with a grain mixture and located at the region of interest on the asteroid is vibrated at that impact’s associated amplitude and frequency. Using this framework, we find that impact-driven seismicity is sufficient to drive size segregation on small rubble-piles, but the segregation quality depends on several aspects, e.g. total impact energy supplied, placement of the region of interest, bulk wave speed and seismic diffusivity.