  The Hayabusa2 mission impact experiment on asteroid Ryugu created an
unexpectedly large crater. The associated regime of low-gravity, low-strength
cratering remained largely unexplored so far, because these impact conditions
cannot be re-created in laboratory experiments on Earth. Here we show that the
target cohesion may be very low and the impact probably occurred in the
transitional cratering regime, between strength and gravity. For such
conditions, our numerical simulations are able to reproduce the outcome of the
impact on Ryugu, including the effects of boulders originally located near the
impact point. Consistent with most recent analysis of Ryugu and Bennu,
cratering scaling-laws derived from our results suggest that surfaces of small
asteroids must be very young. However, our results also show that the cratering
efficiency can be strongly affected by the presence of a very small amount of
cohesion. Consequently, the varying ages of different geological surface units
on Ryugu may be due to the influence of cohesion.
