impacts into granular media at low surface gravity from drop towers include those by @goldman08 [@Sunday_2016; @murdoch17] and in aircraft those by @brisset18. These experiments studied normal impacts so they did not study the sensitivity of the projectile deceleration profile and stopping depth to impact angle. However debris that is orbiting an asteroid that later hits the asteroid surface would be unlikely to only have high or nearly normal impact angles. Grazing impacts of spherical projectiles on sand or water are more likely to bounce or ricochet (e.g., @birkhoff44 [@soliman76; @daneshi77; @bai81]). Simulations by @maurel18 show that this is also true for non-spherical, low velocity projectiles, such as a lander, in low surface gravity.

Images of asteroids 101995 Bennu and 162173 Ryugu show large (10–50 m) boulders that look as if they were perched on the surface [@sugita19; @walsh19]. See Figure \[fig:bennu\] for a boulder that might unstable if perturbed by large amplitude vibrations. Possible explanations for boulders on the surface of a rubble pile asteroids include the Brazil nut effect (e.g., @matsumura14), which drives previous buried boulders to the surface, and boulder stranding that occurs during landing of ejecta that is launched by an impact generated pressure pulse [@wright19]. 