Numerical Investigation of the Cohesive Strength Regime of the Bilobated Arrokoth after the Sky-crater-forming Impact Event

Abstract

In 2019, NASA’s New Horizons mission, using the Long Range Reconnaissance Imager, revealed Arrokoth’s bilobated shape and a large impact-crater-like region (“Sky”) on the small lobe, which is ∼7 km wide and ∼1 km deep. Given that this depression takes up ∼7% of the entire volume of the small lobe, Arrokoth’s neck, the most structurally sensitive area to failure, might have been subject to substantial structural modification if the Sky-crater-forming event occurred after the bilobate shape had formed. Using the π-scaling law, we quantified the linear momentum imparted to the small lobe by the Sky-crater-forming event, which was in the range of (2.4–4.0) × 1013 kg m s−1, depending on Arrokoth’s bulk density of 250–500 kg m−3 and impact speeds of 100 m s−1, 300 m s−1, and 1 km s−1. If the linear momentum was fully transferred to Arrokoth’s small lobe, it would have given the small lobe an impulse velocity of approximately 0.1 m s−1 relative to the large lobe. To assess the structural impact of this event, we used a finite-element modeling approach to simulate post-impact stress fields driven by the estimated impulse velocity on the small lobe and constrained the critical cohesive strength required to prevent structural failure. Based on the current parameter space, our results suggest that the Sky-crater-forming event could have required the critical cohesive strength of up to ∼20 kPa for Arrokoth’s neck to avoid structural failure, which is higher than the typical cohesive strength estimated for small bodies (usually less than 1 kPa for asteroids and comets).