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Abstract
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.
(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.
Purpose
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.
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