Regolith dynamics on small bodies in the Solar System

Many small bodies in the Solar System, such as near-Earth asteroids, are believed to be granular aggregates - rubble piles – held together mainly by low self-gravity, typically of the order of mms−2. Over their lifetime, the evolution of the spin state and shape of such bodies, as well as their bulk and surface differentiation, is affected by numerous geophysical processes that includes radiation, tides, impact cratering, surface activity, thermal cycling, degassing and electromagnetic forces. An ultimate goal is the development of a model that incorporates these processes and is able to follow the body’s development over its lifetime. Here, as a first step, we present a stochastic continuum model to investigate regolith dynamics on small rubble bodies, and its role in the rotational dynamics and reshaping of these bodies. We account for radiation torque and impactinduced landsliding, and couple the body’s rotation to its shape variations. We apply our model to investigate the shape and spin changes of a rubble asteroid over millions of years. An important finding is that the asteroid’s long-term dynamics appears to be controlled by global landsliding events, which has generally been ignored.