  From small seeds falling from trees to asteroids colliding with planets and
moons, the impact of projectiles onto granular targets occurs in nature at
different scales. In this paper, we investigate open questions in the mechanics
of granular cratering, in particular the forces acting on the projectile, and
the roles of granular packing, grain-grain friction and projectile spin. For
that, we carried out DEM (discrete element method) computations of the impact
of solid projectiles on a cohesionless granular medium, where we varied the
projectile and grain properties (diameter, density, friction and packing
fraction) for different available energies (within relatively small values). We
found that a denser region forms below the projectile, pushing it back and
causing its rebound by the end of its motion, and that solid friction affects
considerably the crater morphology. Besides, we show that the penetration
length increases with the initial spin of the projectile, and that differences
in initial packing fractions can engender the diversity of scaling laws found
in the literature. Finally, we propose an ad hoc scaling that collapsed our
data for the penetration length and can perhaps unify existing correlations.
Our results provide new insights into the formation of craters in granular
matter.
