Martian Impact Craters: the Normal and the Unusual

Introduction: Our group has conducted a number of studies investigating the characteristics of martian impact craters. Many of these studies have provided insights into the normal characteristics of martian impact craters, such as their ejecta extents, ratio of central pit diameters to crater diameters, and the distributions of specific ejecta and interior morphologies. Other characteristics are more unusual, such as the extreme ejecta extents of craters in high-latitude regions. Here we summarize the current status of these studies. Crater Catalog Revision: We have completed revision of the northern hemisphere craters except for those in MC12 (i.e., most of Arabia) and MC01D-J (surrounding the north polar cap). The portion completed contains 11360 craters ≥5-km-diameter, compared to the original Viking-based catalog which contains 10395 craters within in the same regional and diameter range. Of these 11360 craters, 4772 (42%) display a classifiable ejecta morphology. 5003 (44%) of the 11360 craters display a classifiable interior morphology. Ejecta Characteristics: The 4772 craters displaying a classifiable ejecta morphology are divided into seven general categories: single layer rampart (SLE), double layer (DLE), multiple layer rampart (MLE), radial (Rd), diverse (Di), pancake (Pn), and pedestal (Pd). Details about ejecta sinuosity are contained in the catalog but are not discussed here. Table 1 shows how the morphologies are distributed.