Material dependency in the scaling of low-speed craters under microgravity with implications for small asteroids

Abstract

Small body surfaces are covered by granular material of varying particle sizes and depths. This material is observed to be easily mobilised from the surface through natural processes or spacecraft interaction. The material can escape or re-impact to the surface as a result of this process. The latter may be considered as a low-speed cratering activity under microgravity. In this paper, a set of simulations of normal impacts at 5–10 cm/s under 9.81 × 10⁻⁵m/s² is presented with gravel-type realistic material properties. The simulated craters are investigated for their qualitative impact outcomes, as well as quantitatively for the coefficient of restitution and crater and ejecta scaling properties. The results are compared with the results of impacts in glass beads type materials from authors’ previous work under the same conditions and wider literature experimental and observational literature. It was shown that most impacts result in a rebound with non-negligible coefficient of restitution values. The crater sizes are smaller compared to those in glass beads material and follows the crater scaling relationships across different impact energies with a μ coefficient of 0.55. Ejection is shown to continue beyond the final size with a significant quantity of material mobilised at speed below escape speed under the selected gravity level. The depth-to-diameter ratio of the craters is within the range of small craters of asteroid Bennu, with qualitative impact outcomes displaying similarities with those found in this paper. These results suggest a possible low-speed impact and secondary cratering activity in small bodies as a result of natural and artificial particle ejection events, such as in the case of Bennu and Didymos.