A universal scaling framework for granular asteroid strength and its application to the surface of asteroid Bennu

Granular asteroids exhibit surprising structural stability despite low gravity and high spin rates. Understanding the mechanisms behind their strength is essential for predicting their evolution and informing deflection strategies. Using 3D particle-dynamics simulations, we develop a scaling framework for the tensile strength of cohesive, self-gravitating regolith, examining how particle size and shape jointly control macroscopic behavior. We show that tensile strength can be scaled using either an equivalent particle diameter or particle shape, the latter through sphericity and its reference to an equivalent spherical packing. We apply this model to asteroid Bennu using data from samples returned by the OSIRIS-REx mission and derive a cohesive surface strength consistent with estimates below 1 Pa from remote sensing and sampling-event reconstructions. Our results indicate that Bennu’s extremely low strength arises from a scarcity of fine dust in its regolith. This study demonstrates how particle-level properties govern large-scale stability and heterogeneity in granular asteroids. Granular asteroids can remain stable despite weak gravity and rapid spin, but the origin of their strength is unclear. Here, the authors show particle size and shape control regolith cohesion and explain Bennu’s very low strength by a lack of fine dust.