How often does junk hit the moon?
This is the first unintentional case of which I am aware. I keep track of a dozen or so objects in "high", near-moon orbits, mostly so that the folks looking for asteroids will know where they are (and can ignore them; they're looking for rocks, not junk.) In theory, given enough time, such objects will either hit the earth, or the moon, or gain energy by passing the moon and be ejected into orbit around the sun.