The rock on the surface of the planet or moon is bent backward, upward, and outward so the amount of material ejected is much larger than the projectile.
Large craters will have a central peak formed by the rock beneath the impact point rebounding upward and they may also have terracing of the inner walls of the crater from the collapsing of the crater rim inward.
Select the image to go to the Selene website for a great flyover of the crater.
Some of them have orbits that cross the orbits of the planets and moons.
When they get close enough to a planet or moon, they will be pulled in by the large body's gravity and strike the surface at a speed of at least the escape velocity of the planet or moon, i.e., faster than a bullet.
Careful studies of how the craters overlap other craters and other features can be used to develop a history or sequence of the bombardment on the moons and planets. Worlds with less volcanism or erosion or tectonic activity in their history will retain more impact craters since the planet formed.
Worlds with more geological or erosional activity will have newer surfaces or craters that have been so worn away as to be unrecognizable.