  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.
