Physics
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p33a1019p&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #P33A-1019
Physics
5415 Erosion And Weathering, 5416 Glaciation
Scientific paper
The presence of an extensive ice-rich layer in the near subsurface of the Martian regolith can result in viscous creep responsible for softening craters at mid and high latitudes. The temperature of ground ice will vary spatially within a crater due the effect of slope on the angle of insolation. The temperature at a particular latitude will also vary due to changes in Mars' obliquity. Results from numerical simulations of viscous flow indicate that these temperature variations cause the pole-facing slopes of craters to be systematically steeper than those of equator- facing slopes. Crater slopes should be most asymmetric between 25 and 40 degrees latitude, depending on the thickness of the creeping layer. This slope asymmetry predicted from theoretical simulations of regolith creep is not well developed in observed Martian crater topography. MOLA topography of craters 16 to 40~km in diameter was analyzed for north-south slope asymmetry within five latitude regions ranging from 60{°}S to 60{°}N. Based on the lack of any systematic slope asymmetry observed in the craters, we can place an upper limit of ~1.2~km on the thickness of the creeping layer assuming a volumetric dust content of 70% and an exponentially increasing soil viscosity with depth. If the creeping layer contains relatively clean ice, then the thickness of ice-rich material is limited to ~600~m or less based on our results. The observations also suggest that the thickness of this creeping layer is reduced by a factor of ~2 towards the equator.
Nimmo Francis
Parsons Robert
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