The Dimorphos Boulder Swarm

Abstract We present deep Hubble Space Telescope images taken to examine the ejecta from DART spacecraft impact into asteroid Dimorphos. The reveal an extensive population of comoving boulders, largest which is ∼7 m in diameter (geometric albedo 0.15 assumed). Measurements 37 boulders show a mean sky-plane velocity dispersion 0.30 ± 0.03 s −1 , only slightly larger than 0.24 gravitational escape Didymos–Dimorphos binary system. total boulder mass, M b ∼ 5 × 10 6 kg (density 2200 −3 assumed), corresponds about 0.1% mass Dimorphos, and collectively carry 3 −5 kinetic energy delivered by impact. distribution asymmetric, consistent with inhomogeneous, likely rubble-pile, body. Surface counts on Didymos that observed swarm could be ejected as little 2% surface Dimorphos (for example, circular crater at point 50 diameter). large, slow-moving are potential targets investigated situ upcoming ESA HERA mission.