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A Revised Modelling of the Strength of Regolith in Asteroids

Presentation #503.01 in the session Asteroids: Main Belt (Oral Presentation)

Published onOct 23, 2023
A Revised Modelling of the Strength of Regolith in Asteroids

The strength of granular asteroids has been the focus of many research efforts as it could explain why asteroids are observed to have high spin rates that exceed their self-gravity. About a decade ago, the source of this cohesive or tensile strength was traced back to the Van der Waals (VdW) forces that exist between any two particles in contact. These VdW forces would allow the small pebbles and dust in a small asteroid to act as a sort of cement that kept the larger rocks and boulders in place, providing the needed strength. This finding was based on granular dynamics simulations carried out with spherical particles, so they also carried the size dependency of the VdW forces with particle size, a first approximation that might not be true for real regolith particles.

New advances in simulation codes have allowed us to improve on those earlier simulation results. In this work, we used non-spherical particles to represent cohesive regolith and carried out the same granular-bridge simulations that are used to directly measure the tensile strength of a self-gravitating granular system. The particles vary in size, size distribution, and axis ratios. Additionally, having in mind that, as thought of many years ago, the roughness of the particles may dictate the magnitude of the cohesive forces, we removed the size dependency and made cohesive forces constant. We found that all these factors affect simulation outcomes, making it possible to obtain the same levels of tensile strength, but with particles larger than previously predicted.

In light of the imminent arrival of samples from the granular asteroid Bennu and their physical analysis by the OSIRIS-REx mission, our results should help us to better model and understand the source of the cohesive strength of the surface and interior of Bennu. Specifically, the OSIRIS-REx mission will conduct direct measurements of the cohesive forces between Bennu particles. Those results will help calibrate our models of the bulk strength properties of the asteroid itself.

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