Predictions for the interior of asteroid Dimorphos through the DART-scale impact modeling

In recent years, space missions have made significant progress in characterizing Near-Earth Asteroids (NEAs), from JAXA's Hayabusa2 mission on Ryugu to NASA's Double Asteroid Redirection Test (DART) mission, which demonstrated a successful kinetic impact on Dimorphos, the secondary of 65803 Didymos binary asteroid system [1]. In the seconds before the impact, the DART spacecraft imagery captured a boulder-strewn surface of Dimorphos. Numerical impact simulations, meanwhile, studied the aftermath of the DART impact to understand the potential cratering and ejecta outcomes through shock physics modeling [2], nevertheless the subsurface remains largely unknown. To explore the internal features of Dimorphos, we simulated a series of DART-scale hypervelocity impacts using the two-dimensional axisymmetric (2DC) version of the iSALE shock physics code [3-5]. Impacts were modeled over longer timeframes on half-spheroidal targets to resolve the surface curvature effect on Dimorphos, incorporating recent mechanical and material constraints from the DART impact [6,7]. Various internal scenarios were tested, ranging from simplified homogeneous to layered heterogeneous interiors with multiple boulders near the impact site. The time evolution of the crater size, ejecta, and momentum transfer efficiency, β, were tracked across simulated scenarios. The results suggest plausible interior scenarios for Dimorphos, whether homogeneous or heterogeneous, that align with the observed β range for the DART impact [8]. Simulations of homogeneous interiors with low cohesions (10-50 Pa) fell within the reference β range when the coefficient of internal friction was set at 0.5, assuming Dimorphos has the same bulk density as the binary system. In addition, decreasing porosity or increasing the friction coefficient led to cohesion values that matched the reference β, approaching 1 Pa. In heterogeneous scenarios, a double-layered interior containing a loose outer layer atop a weak core and a three-layered interior with multiple boulders concentrated at the impact site produced β aligning with the reference β, indicating the potential for diverse interiors in Dimorphos. These findings offer new predictions for the cratering and interior structure of Dimorphos, which the ESA Hera mission will probe [9] during a rendez-vous from a unique proximity in late 2026.

References

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