A Universal Scaling Framework for Granular Asteroid Strength and its Application to Bennu's Surface

Granular asteroids can exhibit unexpected structural stability despite their low gravity and rapid spin rates. Understanding the physical mechanisms underlying their strength is crucial for predicting asteroid evolution and designing deflection strategies. Here, using three-dimensional particle dynamics simulations, we develop a scaling framework for the tensile strength of cohesive, self-gravitating regolith matrices, focusing on the combined effects of particle size and shape. Surprisingly, we find that the tensile strength of granular systems can be effectively described by a single parameter—either equivalent diameter or sphericity—despite the geometric complexity of the constituent particles. We then apply our model to the granular asteroid Bennu by using physical data from regolith samples returned by the OSIRIS-REx mission. We find a cohesive surface strength that is consistent with estimates (< 1 Pa) based on remote sensing and reconstruction of the sampling event. Our analysis suggests that a scarcity of dust in Bennu’s regolith drives its low surface strength. This work provides broad insights into how particle-level properties influence macroscopic stability, shedding light on the structural integrity and heterogeneity of granular asteroids.