The Distribution of Craters Within Craters

The interior of a crater should have a lower mean areal density of smaller impact craters than nearby plains have, because the impacts are spread out over a larger surface area, and because the crater’s wall partially shields its interior. Inside a crater shaped like a spherical bowl (a spherical cap turned upside-down), smaller primary impact craters should be spread uniformly, but secondary craters have a more complicated distribution, usually concentrated near the center. These results may help to distinguish between populations of primary and secondary craters, and should be of interest for interpreting counts of craters within craters.