Effects of Surface Topography on the Crater Formation Process of Rubble-Pile Asteroids

Abstract Introduction Hayabusa2, the Japanese asteroid exploration mission, conducted an impact experiment on the surface of asteroid Ryugu to create an artificial crater. An observed crater measuring 14 m in size, filled with boulders, formed in the gravity-dominated regime, even in the microgravity environment of ~10-5 G on Ryugu [1]. The study revealed that the artificial crater’s size was well reproduced by the crater size-scaling law for dry sand, suggesting that dry sand can simulate the surface of small rubble-pile bodies rich in boulders in terms of the crater formation process. NASA’s DART mission recently conducted a successful large-scale impact experiment on Dimorphos, a small satellite of asteroid Didymos (~200 m in diameter). The mission demonstrated a significant momentum transfer efficiency exceeding =3 during the impact of the DART spacecraft [2]. Considering Dimorphos’s boulder-covered surface, similar to Ryugu, the resulting crater may grow in the gravity-dominated regime. The  is theoretically sensitive to the momentum of ejecta during cratering and if the value is larger than 1, it strongly depends on the amount of ejecta and the velocity-mass relationship. In addition to the ground-based observation of the orbital period of Dimorphos [2], LICIA-Cube, following the impacting spacecraft, successfully made an in-situ observation of the DART impact event [3], and more the Hubble space observatory observed the ejecta curtain growth after the DART impact [4].