Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p41b1363o&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P41B-1363
Physics
0710 Periglacial Processes, 5420 Impact Phenomena, Cratering (6022, 8136), 5462 Polar Regions, 5464 Remote Sensing, 6225 Mars
Scientific paper
Many HiRISE images have resolution approaching 10 cm/pixel. At this resolution, individual rocks on the surface are clearly observable, and we are examining these rock size- and spatial distributions for evidence of soil convection and rock migration, in our pursuit of understanding Martian atmospheric/soil interactions in the present and most recent epoch. Our hypothesis is that in many of the plains on Mars there exists an active layer a few m to 10's of m thick that causes convective patterning and migration of rocks of various size. While the cause of pattern formation and rock migration is widely open to debate (Noe Dobrea et al. Mars Caltech 2007; Mellon et al. JGR in press 2008) and likely involves multiple mechanisms separately or in combination, an important initial task is to obtain data for rock size and spatial distributions in patterned ground, for the purpose of establishing and testing the varying hypotheses. In certain terrain in the northern hemisphere of Mars, rocks are observed to arrange themselves into geometric patterns, in association with topographical deformations reminiscent to patterned ground on Earth. Patterned ground in arctic tundra is known to form when growth and loss of interstitial ice in the active layer of the surface (freeze-thaw) cause net displacements of the soil. These displacements, aggregated over time, transport rocks to and along the surface into the patterns we see (Kessler et al. Science 2003). While freeze-thaw is difficult to sustain on Mars in the present epoch, and seemingly impossible below a few millimeters, it appears that some process is active in the upper meters which creates decameter-scale patterns and moves meter scale rocks and boulders. Small, recently-formed craters are the obvious candidate in our search for clues. Polygonal patterned ground is found to cover and consume many small craters in the northern hemisphere of Mars. HiRISE images show polygonal patterned craters with much higher rock count density than polygonal patterned terrain in non- cratered regions. Impacts may be responsible for the source and initial distribution of rocks that polygonal patterned ground now act upon. Furthermore, the geometric patterns themselves may be influenced due to the quantity of rocks on the surface. Here we report two findings: (1) the distribution of rocks on the surface with distance from the center of each crater identified that is in the process of being consumed by patterning, and (2) the smallest craters identified to date in various types of patterned ground.
Asphaug Erik
Kreslavsky Mikhail
Orloff T. C.
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