The boulder size-frequency distribution derived from DART/DRACO images of Dimorphos: Preliminary results

On 26 September 2022, the Double Asteroid Redirection Test (DART) spacecraft impacted the surface of Dimorphos, the ~150 m size satellite of the near-Earth binary asteroid (NEA) (65803) Didymos (~780 m-size, [1]). Numerical models of asteroid disruption, the analyses of asteroids' shapes, and in situ observations, support the interpretation that small asteroids (0.2-10 km size range) are reaccumulated remnants from disrupted parent bodies, also called rubble-piles (e.g. [2, 3]). Surface boulders, therefore, represent directly the fragments of those parent-body disruptions followed by some evolutionary process such as cratering and thermal breakdown, followed by the size-sorting and migration of granular materials when an asteroid's regolith is mobilized. Hence, the observed size-frequency distribution (SFD) of boulders on the surface of a NEA and the corresponding fitting indices is a powerful tool for understanding the initial formation of boulders and their subsequent evolution. The boulder SFD is also important in understanding the conditions of the surface for any kinetic deflection experiment such as DART.