The dynamic corridor of regolith transportation near a spinning-up asteroid

Abstract

The transport of regolith material has been confirmed by in situ exploration missions to asteroids like Itokawa, Ryugu and Bennu, providing evidences for the topographic evolution of these minor planets. This paper studies the migration of disturbed regolith materials across the asteroid surface from the viewpoint of nonlinear dynamics. We propose a simplified two-dimensional model that captures the dynamics of the regolith migration in a strongly perturbed environment, considering the non-spherical gravitational field induced by a massive body of irregular shape. We choose the shape of the equatorial cross-section of asteroid (101955) Bennu as a representative case. The transport paths of surface particles in terms of the spin-up process are identified. By checking the accessible/forbidden regions in the vicinity of the asteroid, we find that at low spin rates, regolith particles are confined to the vicinity of their initial positions and the motion area is sketched by the boundary of the zero-velocity curve. As the spin rate increases, we observe the formation of a notch that connects the two divided parts of the accessible regions, which creates a C-shaped corridor. Through this corridor, particles can enter cycling orbits around the asteroid, forming a continuous flow of mass movement. The long-term transport tendency of the surface material is found to be governed by this corridor. A higher spin rate enhances the occurrence of large-scale transport of particles across the asteroid surface. Using the methodology developed in this paper, we provide a perspective on the long-term transport dynamics of regolith materials, and it helps us to achieve a macro-analysis of the mass redistribution during the slow spin-up process of an asteroid.