The shape and structure of small asteroids as a result of sub-catastrophic collisions

Abstract

The overall shape, internal structure and surface morphology of small bodies such as asteroids and comets are determined to a large degree by the last global-scale impact or disruption event. Depending on the specific energy, impacts lead to a large spectrum of outcomes. Sub-catastrophic disruptions take place in an energy range between cratering impacts and catastrophic disruptions. Although less energetic than catastrophic events, they can still significantly alter the overall shape and structure of the target body. This has been demonstrated recently in the case of bi-lobe cometary nuclei (Jutzi and Benz, 2017). Here we present results of a subsequent study on the shapes of asteroids resulting from such collisions. Sizes ranging from a few hundred meters to a few kilometers are considered.We show that impacts on elongated rotating asteroids frequently lead to the formation of contact binaries. Our results confirm that this mechanism is robust and works for a large range of asteroid sizes and impact velocities. Scaling-laws for the prediction of the size and velocity dependent specific energies required for successful bi-lobe formation are presented. Based on these scaling laws, the expected frequency of such sub-catastrophic impacts is calculated and is compared to the one of catastrophic disruptions, which require much higher specific energies and are more rare.Our analysis suggest that the shapes and structures of a large fraction of small asteroids as observed today may be the result of the last major sub-catastrophic impact.