Martian impact craters: Correlations of ejecta and interior morphologies with diameter, latitude, and terrain

The premise of this study is that global analysis of crater morphologies can discriminate between the effects of impact energy, atmosphere, and subsurface volatiles based on the correlation between morphology and latitude, diameter, and terrain. This study focuses on seven ejecta and nine interior morphologies associated with 3819 craters ≥8 km in diameter distributed across the entire Martian surface. This data set is sufficiently large to provide statistically viable results on a global scale. The results of the analyses indicate that changes in ejecta and interior morphology correlate with increases in crater diameter. Excavation depths corresponding to these diameters are calculated from depth-diameter relationships and are compared to the theoretical distribution of subsurface volatiles. The different ejecta morphologies can be described by impact into material with varying proportions of volatiles, and the latidudinal variations seen for rampart crater morphologies correlate well with the proposed latitude-depth relationship for ice and brines across the planet. Many of the interior structres show distributions indicative of terrain-dependent influences: for example, the concentrations of central pit craters around ancient impact basins and on Alba Patera suggest that volatiles preferentially collect in these areas. However, central peak and peak ring interior morphologies show little relationship to planetary properties and probably result from changes in impact energy. Thus, many of the unique morphologies associated with Martian impact craters result from the presence of subsurface volatiles.