HiRISE Images of the Sublimation of the Southern Seasonal Polar Cap of Mars

Details HiRISE Images of the Sublimation of the Southern Seasonal Polar Cap of Mars HiRISE Images of the Sublimation of the Southern Seasonal Polar Cap of Mars

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p24a..04h&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #P24A-04

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6225 Mars

Scientific paper

The High Resolution Imaging Science Experiment (HiRISE) on the Mars Reconnaissance Orbiter (MRO) has returned images with unprecedented resolution of Mars southern seasonal CO2 polar cap. Several high latitude sites were selected for systematic monitoring throughout the spring as the seasonal cap sublimed away. The capability of MRO to turn off-nadir enabled acquisition of stereo pairs to study the topography. HiRISE color capability distinguishes processes involving dust and frost. Color images show evidence of localized migration of frost as dark spots sublimate. Unique landforms are found in the cryptic terrain[1] region of Mars polar cap. These unusual landforms have narrow channels emanating radially, dubbed spiders[2]. Fans of dust blown by the prevailing wind are hypothesized to come from gas jets of CO2 subliming beneath translucent seasonal ice [3]. HiRISE images show a wide variety of morphologies of narrow channels. In some regions deep narrow channels converge radially, while in others the high channel density is more akin to lace. A smooth evolution of one form to another has been observed. Channels converge dendritically, often uphill, consistent with formation by flowing gas, not liquid. More dust fans are observed in regions of spiders than in lace, suggesting that the sublimating gas under the seasonal ice builds up more pressure and can entrain more dust in spidery areas. These differing terrain types are found within a single 6 x 10 km image, which has presumably homogeneous weather, thus a uniform layer of ice and exposure to atmospheric dust. HiRiSE images show that the dust fans tend to emerge from low spots, where the subsurface is accessed, then are blown up and out onto the surface of the seasonal ice. The fans evolve from a thin diffuse covering to thick blankets filling in the narrow channels. We hypothesize that dust collects in the channels, and that these relatively more permeable dust-filled channels form pathways for the next seasons gas to escape from below, a positive feedback which would tend to erode the same channels a little more every season. In another region of the cryptic terrain the surface has a texture reminiscent of lizard skin. Fans are seen to form and grow in a time period of less than 5 days, evidence for a very active process modifying the martian landscape. We also see the formation and disappearance of bright streaks within a short time interval. There are also sand dunes at high latitudes that get covered with seasonal frost. Dry ice is affecting the landscape and may be responsible for the formation of gullies on dunes. [1]Kieffer, H., (2000) LPI #1057. [2]Piqueux, S., S. Byrne, and M. Richardson, (2003) JGR 108(E8):3-1. [3]Kieffer, H., (2006) accepted for publication in JGR. This work was partially supported by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

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