Mathematics – Logic
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p31c0549k&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #P31C-0549
Mathematics
Logic
5405 Atmospheres (0343, 1060), 5415 Erosion And Weathering, 6225 Mars
Scientific paper
Slope streaks are forming in some equatorial regions on Mars. They have been mostly interpreted as a result of dry mass wasting of dust. Recently a striking morphological similarity with wet slope streaks in the Antarctic Dry Valleys has been demonstrated. Physical conditions on Mars do not allow the same mechanism. We propose a "wet" mechanism on Mars, which inherits the main feature of the Antarctic slope streaks responsible for their distinctive planforms, namely, shallow subsurface percolation of liquid above the ice table. This mechanism assumes some ice in the shallow subsurface, which had been emplaced under previous wetter climate conditions and currently is undergoing slow desiccation. This icy soil is overlaid by a layer highly enriched in chlorides. On top of this layer, there is a thin layer of dry fine dust. During the warm season, droplets of highly concentrated brines are formed in the salty layer. Sometimes at some places, the droplets coalesce; the liquid percolates downhill, wicks up through the dust layer and dries up. This alters the uppermost dust layer structure, which affects the surface albedo and observable as a dark streak. Further gradual changes of this new surface structure lead to slow brightening of the streak and final fading away. Such a mechanism is at the margin of physical possibility and consistency with observational constraints. Prospective observational tests for "wet" mechanism: (1) Spectral signature of hydrated chlorides in fresh streaks, would make "wet" hypothesis much more probable. (2) Gentle slope of slope streaks, especially of their uppermost parts would strongly favor "wet" mechanism. (3) Observation of slope streak formation during cold seasons, when the day-average surface temperature is below 190 K would reject "wet" mechanism. (4) Observation of a slope streak in the process of formation (a streak that lengthens from earlier to later image) would almost prove "wet" mechanism, at least, almost reject dry avalanche scenario. (5) Absence of a shallow high-thermal-inertia layer would be inconsistent with a "wet" scenario. (6) Geomorphologic observations supporting subsurface ice in the slope streak regions would favor the "wet" mechanism.
Head James
Kreslavsky Mikhail
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