Spherical multi-lacunarity reveals possible equatorial-polar differences in crater densities on the dwarf planet Ceres

Abstract

The dwarf planet Ceres possesses a peculiar distribution of impact craters. It has been previously noted that the largest craters expected for Ceres are absent, while for smaller craters, the north polar region is the most heavily cratered. It thus appears that some process(es) have erased some of Ceres' craters, and the distribution of observed craters could point to the nature of these processes. For instance, a process tied to sunlight (e.g., relaxation or sublimation) could impart a latitudinal dependence, while a more regional distribution could point to a more endogenic process (e.g., cryovolcanism). Through a combination of spherical multi-lacunarity analysis and kernel density maps, we discover that the 20 largest craters (> 100 km across), though statistically indistinguishable from random, are stochastically concentrated in the south, while mid-size craters (20–70 km) show clustering at spatial scales >130 km, roughly the same scale that would be affected by emplacement of the 20 largest craters plus ejecta. A mask made from these largest craters plus ejecta reveals that a south polar region that matches the heavily cratered north is almost completely covered by the largest craters. Crater counts additionally reveal that this north polar region is older (i.e., more heavily cratered) than an equatorial region not masked by the largest craters, which in turn is about as cratered as the oldest of the 20 largest craters. Thus, it appears that there could be equator-polar differences to Ceres' crater distribution, or at the very least, that a latitudinal dependence cannot be discounted. Consequently, latitudinal variations in sunlight might be a controlling factor in the distribution of craters on Ceres.