Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p31a0115p&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #P31A-0115
Physics
5418 Heat Flow, 5422 Ices, 5462 Polar Regions, 6225 Mars
Scientific paper
A 3D model for the coupled evolution of ice-surface temperature and elevation in the martian polar ice caps is presented. The model includes (1) enhanced heat absorption on steep, dust-exposed scarps, (2) accumulation and ablation, and (3) lateral conduction of heat within the ice cap. The model equations are similar to classic equations for excitable media, including nerve fibers and chemical oscillators. In 2D, a small zone of initial melting in the model develops into a train of poleward-migrating troughs with widths similar to those observed on Mars. Starting from random initial conditions, the 3D model reproduces spiral waves very similar to those in the north polar ice cap, including secondary features such as gullwing-shaped troughs, bifurcations, and terminations. The role of the ice-cap geometry in controlling the spacing and morphology of troughs is emphasized. Martian polar chasmata are large (~ 100-km wide, ~ 500 km long) canyons or embayments formed at the margins of the polar ice caps. The floors of these chasmata have a smaller albedo and hence a larger surface temperature than the surrounding ice. Here I propose that chasmata form when spiral troughs deepen sufficiently near ice-cap margins to expose the underlying low-albedo substrate, providing a heat source for ice-cap ablation and the formation of a thermal "dendrite" that widens and penetrates into the ice cap interior. I model this chasmata-formation process as a Stefan problem (i.e. the motion of a phase boundary driven by a thermal gradient) with a curved boundary. Analytic solutions to this model predict parabolically-shaped chasmata with tip radii of ~10 km in regions of 2-km-thick ice, with proportionately smaller radii in regions of thinner ice. Spatial analyses of Chasmata Boreale and Australe are consistent with this prediction.
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