Presentation #311.02 in the session “Mars Surface”.
Impacts on Mars occurring in the present day were first found using MGS MOC (Malin et al., 2006). The Context and HiRISE cameras on MRO have been continuing these discoveries and expanding this dataset for over a decade (e.g. Daubar et al. 2013). These new impacts allow for studies of not only impact cratering processes, but also atmospheric fragmentation processes, weathering processes, and both high energy and aeolian atmosphere-surface interactions. Specifically, they have allowed studies of the current impact rate and calibration of Martian chronologies, the morphology of fresh simple craters, characteristics of clusters, albedo patterns around new impacts, exposed subsurface ice and mafic materials, and predictions of the seismic effects of impacts.
Although partial lists have been published previously, we are gathering all known sites in a single unified catalog to be made available to the community. Updated statistics will be presented at the meeting, but our preliminary catalog includes more than 1,000 impact sites, each with formation date constraints from orbital imaging. The largest new crater is ~60 m in diameter, and ~15 are >20 m. Slightly over half are primary clusters, where the impactor fragmented in the atmosphere to create from two to several hundred individual craters, extending over as much as several km. Most known new impacts are in regions of Mars with low thermal inertia; their discovery seems to require a loosely consolidated surface layer overlying a contrasting albedo substrate, and/or textural changes that cause an albedo contrast. The before and after images on the new impacts include data from many orbital cameras. The constrained formation time periods range from 1 day to >30 Earth years, averaging 4 Earth years. The mixture of limiting dates and different datasets used as constraints make using this catalog to measure the current impact rate a complex problem, but we can compare slopes of size-frequency distributions of current impactors even without scaling to an area-time factor.
This will represent a useful dataset for many applications. Investigations of the dependence of various features (e.g. rays, halos) on terrain type will elucidate formation mechanisms. Information about the cluster crater dataset is leading to new understandings of atmospheric fragmentation mechanics. Our hope is that the community will find this catalog useful in many other studies as well.