Simulating NASA DART impact: Insights into the interior of asteroid Dimorphos

Impacts are commonplace in our Solar System, constituting one of the key mechanisms that regulate the evolution of asteroids and comets. From small-scale Martian meteorites to large biosphere-forming collisions, e.g., the Chicxulub catastrophe at the end of the Cretaceous Period, impact events are essential to understanding the dynamic history of planetary bodies. In recent years, asteroid missions have made major advancements in characterizing the Near-Earth Objects (NEOs), from JAXA's Hayabusa2 sample-return mission on asteroid Ryugu to NASA’s recent DART space mission that performed the first kinetic deflection on asteroid Dimorphos [1]. The upcoming Hera mission by the European Space Agency (ESA) will characterize the DART impact during a rendezvous with Dimorphos in 2026. Meanwhile, numerical simulations have studied the potential impact cratering and ejecta plume outcomes in response to the DART-scale impactor [2]. Yet, interior features of near-Earth asteroids remain unknown. Understanding what lies inside Dimorphos, various interior scenarios are tested by combining shock physics modeling with the outputs of ejecta observations. The observed ejecta outcome makes it possible to groundtruth modeled ejecta. Therefore, a series of hypervelocity impact simulations are performed through the iSALE2D shock physics code [3-5], incorporating recent mechanical and material parameters [6,7]. Additionally, the DART spacecraft is approximated to be a porous aluminum sphere. The impactor vertically collides at a speed of 6.145 km/s, with Dimorphos taken as an axisymmetric ellipsoid. We test the DART impact within the low-to-intermediate strength regime (1 Pa - 1 kPa) with a wide porosity range (10 - 50%) for a homogeneous interior. This process is iterated for heterogeneous interiors consisting of multiple weak or strong inner layering with or without core formation and boulders. The model results provide new predictions for the plausible cratering formation, thus key insights into the interior of Dimorphos.