Small Impact Crater Clusters in High Resolution Hirise Images

Introduction: Impact crater clusters or crater strewn fields from primary impacts are found in MOC [1, 2], CTX, and HiRISE images [3, 4]. We present the analysis of new data on small craters and crater clusters accumulated by the HiRISE team for the first 10,000 orbits of MRO. New Craters on Mars: Repetitive imaging of Mars by various spacecraft revealed 20 potential " new " impact sites [2]: impact craters with documented time periods of formation, assuming that the appearances of dark spots correspond to crater formation. During the first ~6,000 orbits HiRISE was targeted to the same sites and confirmed 19 of these as pristine impact locations. By late 2008 data from ~10,000 MRO orbits had been released and processed increasing the number of recognized " new " craters by a factor of 2. As of 7 Jan 2009 70 new impact sites have been discovered (mostly by CTX) and confirmed by HiRISE. Crater location. Most of " new " impact sites are located in the same dusty areas where the primary MOC collection [2] had been gathered. 2 impact sites are located well beyond the MOC collection area. The most interesting is the most Southward impact site in Hellas (PSP007596_1295, 50.2N, 70.1E) ~6.36 km below zero topographic level (Fig.1). Crater type. For the first 19 very recent impact sites a single crater or one major crater formed in ~65% of impacts (12 of 19 cases). Prominent multiple clusters (5 of 19) and " overpopulated " clusters (2 of 19) account for ~35 % (7 of 19) of impacts. In the extended " 10,000 orbits " database a single crater or one major crater formed in ~53% (21 of 40) and prominent strewn fields are observed in ~47% (19 of 40) cases. Cluster characteristics: We measure the diameters of all detected craters in each cluster and use the value of D eff =(ΣD i