The project extends the ISSI workshop project on Evolution and Chronology of Mars (Kallenbach et al. 2001), and our own earlier ISSI team studies (2007-2009). We will extend the Martian chronology system by an order of magnitude in crater diameter by measuring the shape of the size-frequency distribution (SFD) of newly produced Martian craters, down to craters of diameter D only ~ 1 or 2 meters, now being imaged by the HiRISE camera. We will combine this result with the 2006 measurement of the production rate of decameter craters, from Malin et al. (2006). With the SFD shape in the 1-20 m range, and the production rate in the 10-20 m range, we can open the door to utilizing these smallest craters to date surfaces of small (km scale) geologic formations on Mars, such as individual lava flows, landslides, deltaic fans of gullies and channels, etc.



576 MARS Impact explosion WKHok small.jpg

(Copyrighted acrylic painting by team member William K. Hartmann, Planetary Science Institute, Tucson.)

View of a small-sized crater-forming event on Mars.  A projectile (which may be a secondary fragment from a larger distant crater-forming event) has just struck the surface.  The painting shows a typical "curtain" of ejected fragments launched at about 45 degrees, plus the "base surge" if disrupted material on the surface.  The even will produce a crater about 100m across on Mars.  





Nature stamps out circles (impact craters) at measurable rates on  planetary surfaces.  This circumstance provides a valuable geological tool for measuring ages of the surfaces, as has been explored by ISSI projects in the past.  (See the ISSI book,  Chronology and Evolution of Mars, Eds. R. Kallenbach, J. Geiss, and W. K. Hartmann.  Eds. R. Kallenbach, J. Geiss, and W. K. Hartmann.  (Bern: International Space Science Institute; also Space Sci. Rev., 96, pp. 165-194.)       Moreover the impact craters offer opportunities to characterize the nature, and rates of geological processes.  The craters form on mars with a particular size-frequency distribution (SFD) on the Martian surface.  In principle, the initial or “production” size frequency distribution (PSFD) can be measured on young, pristine surfaces where there has been little modification, dust cover, etc.  This measurement has been made and improved since the 1960, starting with very large craters, and working to smaller sizes as spacecraft imagery gets better.  An example is given in Figure 1, which shows counts prepared during our first two workshop meetings, in November 2010 and May 2011.