A proposed explanation of how craters and basins become more shallow with size

Figure 1: The depth to diameter ratio of craters smaller than a certain size is a constant, as predicted by the Maxwell Zmodel. Below a break point (10 km for the Moon), the ratio follows a power law, decreasing as size increases [Hiesinger, 2006, Sharpton, 1994]. Source: [Hiesinger, 2006]. The uniformity of the phenomena suggests that there are two excavation processes, one for features with a size below the break point and another for larger features. Insight might be gained by looking for a break point parameter that is common among the target bodies. A common break point parameter: As can be seen from Figure 1, this phenomenon occurs on all rocky bodies, with remarkable consistency, except for the size where the break occurs. One important parameter of the different bodies is the surface gravity, which is obviously relevant to the excavation process (in the gravity regime for these craters). Both diameter and depth of craters at the break point have been found to be inversely proportional to surface gravity (Melosh, 1989). The parameters related to the break points, along with the ambient pressure at the break point depth, are shown in Table 1. Table 1: Break point parameters Feature Break Point Surface g Pressure Diameter Depth km km m/sec 2 kg/ m 2