Some of the surface boulders on Bennu are so large they probably instead landed on the surface during accumulation following a disruptive large collision of larger asteroids [@walsh19].

A low velocity boulder projectile with a shallow or grazing impact angle might bounce off the surface, landing distant from the site of first impact and from any depression in the surface resulting from material ejected during its first impact. We consider ricochets of low velocity impactors as a way to account for protruding boulders on Bennu and Ryugu’s surfaces. While Bennu and Ryugu might lack surface regions comprised primarily of fine grained material, other asteroids such as 433 Eros [@veverka01; @cheng02], 25143 Itokawa [@miyamoto07] and the moon exhibit smooth regions covered in regolith. The dynamics of low velocity grazing impacts into granular media is also relevant to interpretation of the surfaces of these bodies and for the design of landers that may be going to them. For a review of granular media in solar system bodies see @hestroffer19.

![A perched boulder is 47 ft (14.3 m) long on Bennu. From <https://www.asteroidmission.org/20190405-shelf/> This image was taken by the PolyCam camera on NASA’s OSIRIS-REx spacecraft on April 5 2019 from a distance of 