When two objects smash into each other, they usually leave evidence of impact. High speed contact between a baseball and a window tends to result in a lot of broken glass. Drop a bowling ball into a sandbox, and sand goes flying out. Do the same with a balloon and… Raindrops leave marks on puddles, even if temporarily.
We can make some predictions on the size, duration, and amount of destruction a particular impact will cause by examining the physical properties of the projectile. And by looking at an impact crater, we can make some guesses as to what kind of object was responsible for this damage.