Ryugu's observed volatile loss did not arise from impact heating alone

TL;DR

This study investigates the causes of volatile loss in asteroid Ryugu, demonstrating that impact heating alone cannot explain the depletion, and suggests additional processes are involved.

Contribution

The paper provides experimental evidence that impact heating is insufficient to account for Ryugu's volatile loss, highlighting the need for alternative explanations.

Findings

Impact experiments show limited volatile loss from impacts.

Impact heating alone cannot explain Ryugu's volatile depletion.

Additional processes are likely involved in volatile loss.

Abstract

Carbonaceous asteroids, including Ryugu and Bennu, which have been explored by the Hayabusa2 and OSIRIS-REx missions, were probably important carriers of volatiles to the inner Solar System. However, Ryugu has experienced significant volatile loss, possibly from hypervelocity impact heating. Here we present impact experiments at speeds comparable to those expected in the main asteroid belt (3.7 km s-1 and 5.8 km s-1) and with analogue target materials. We find that loss of volatiles from the target material due to impacts is not sufficient to account for the observed volatile depletion of Ryugu. We propose that mutual collisions in the main asteroid belt are unlikely to be solely responsible for the loss of volatiles from Ryugu or its parent body. Instead, we suggest that additional processes, for example associated with the diversity in mechanisms and timing of their formation, are necessary to account for the variable volatile contents of carbonaceous asteroids.