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Astrodynamics

Article Title

Structural analysis of rubble-pile asteroids applied to collisional evolution

Keywords

asteroids interior structure, geological processes, N -body simulations, gravitational aggregates, meteorite impacts

Abstract

Solar system small bodies come in a wide variety of shapes and sizes, which are achievedfollowing very individual evolutional paths through billions of years. Nevertheless, somecommon mechanisms can still be found during these processes, e.g., rubble-pile asteroidstend towards fluid equilibrium as they are reshaped by external disturbances. This paperfocuses on the reshaping process of rubble-pile asteroids driven by meteorite impacts. Amesoscale cluster of solid spheres is employed as the principal model for a rubble-pileasteroid, for which little is actually known about their interior structure. We take thissimple model as a rough guide to the qualitative aspects of the reshaping processes, andit can reveal, to some degree, the inner workings of rubble-pile asteroids. In our study,numerous possible equilibrium configurations are obtained via Monte Carlo simulation,and the structural stability of these configurations is determined via eigen analysis of thegeometric constructions. The eigen decomposition reveals a connection between the cluster’sreactions and the types of external disturbance. Numerical simulations are performed toverify the analytical results. The gravitational N -body code pkdgrav is used to mimicthe responses of the cluster under intermittent non-dispersive impacts. We statisticallyconfirm that the stability index IS, the total gravitational potential PG, and the volumeof inertia ellipsoid VE show consistent tendency of variation. A common regime is foundin which the clusters tend towards crystallization under intermittent impacts, i.e., onlythe configurations with high structural stability survive under the external disturbances.The results suggest the trivial non-disruptive impacts might play an important role in therearrangement of the constituent blocks, which may strengthen these rubble piles and helpto build a robust structure under impacts of similar magnitude. The final part of this studyconsists of systematic simulations over two parameters, the projectile momentum and therotational speed of the cluster. The results show a critical value exists for the projectilemomentum, as predicted by theory, below which all clusters become responseless to externaldisturbances; and the rotation proves to be significant for it exhibits an “enhancing” effecton loose-packed clusters, which coincides with the observation that several fast-spinningasteroids have low bulk densities.

Publisher

Tsinghua University Press

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