Regolith resurfacing and shedding on spinning spheroidal asteroids: Dependence on the surface mechanical properties

Abstract

Context. The Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect has been shown to effectively alter the rotational status of asteroids. The spin-up of the asteroid leads to surface instability and eventually triggers regolith failure, followed by landslide and mass shedding on the asteroid’s surface. Aims. We explore the dynamics of the rotation-induced resurfacing and shedding, paying special attention to the dependence of post-shedding evolution on regolith mechanical properties, such as cohesion. Methods. We propose a qualitative semi-analytical model to explore the post-failure dynamics of a fast-rotating asteroid. We also consider the interaction between the surface mass rearrangement and the asteroid’s spin status. We used our model to investigate the surface region where the failure occurs, as well as the total mass shed from the surface and the spin-down of the asteroid in this process. Results. Based on our model, all the possible avalanche events following a regolith failure can be classified into four basic types: resurfacing (ReS), shedding and resurfacing (S&ReS), shed and bound (S-Bound), and shedding and escaping (S-Escp). Their corresponding regions in the parameter space are illustrated in this work. Our results show that although the regolith cohesion is very small (≲1–2 Pa), cohesion plays an important role in the onset of the avalanche. Moreover, our model qualitatively reconstructs the links between the regolith’s properties and the dynamical fates of the shed material. The timescale of YORP-induced shedding events is also discussed in this work.