Axisymmetric landslides on small planetary bodies

We aim to understand how landslides affect the shape and rotational motion of small rubble planetary bodies. We limit ourselves to axisymmetric global landslides and take the primordial shape of the body to be axisymmetric as well. The landslides are modelled as shallow granular surface flows using depth averaging, while incorporating the effects of the body’s rotation, topographical changes from previous landslides, its non-uniform gravity field and possible surface mass shedding. The body’s rotational dynamics is coupled to its shape change due to the transport of regolith – surface grains – and also accounts for the influence of radiation torque. We utilise our framework to investigate regolith motion on idealised rubble bodies and actual asteroids. We then study the evolution of the shape and spin state of an initially spherical rubble asteroid undergoing multiple global landsliding events over millions of years – a time scale comparable to typical asteroidal lifetimes. We find that shape changes due to landsliding resist spin-up due to radiation torque and, in some instances, may even cause the body to spin down. Furthermore, rotational fission is delayed, and may even be suppressed, by regolith redistribution toward the body’s equator. Finally, top-shaped configurations may emerge rapidly, which may explain the prevalence of top-shaped asteroids in near-Earth orbits.