The longer the surface has been exposed to space, the more craters it will have.If you know how frequently craters of a given size are created on a planet or moon, you can just count up the number of craters per unit area.
At such speeds, the projecticle explodes on impact and carves out a round bowl-shaped depression on the surface. How can you distinguish an impact crater from a volcanic crater?
Volcano craters are above the surrounding area on mountaintops while the craters from impacts are below the surrounding area with raised rims.
Also the pressure from the surrounding solid rock squeezes the molten rock upward.
Molten rock contains trapped gases that expand as it rises causing it to rise even faster.
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.The last stage of that "sweeping up", called the occurred from about 4.1 to 3.8 billion years ago.Impacts as large as the one that led to the demise of the dinosaurs in much more recent history were happening about once a month.The craters on all of the moons except Io, Mercury, and most of the ones on Mars are from impacts.The kinetic energy of the impacting meteorite or asteroid is converted into heat, sound, and mechanical energy---the projectile explodes on impact.The first frame of a 3D movie flyover of Tycho Crater on the Moon as seen by Kaguya. It displays the classic terraced crater walls and central peak of a complex crater.