Mathematics – Logic
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p51b1426r&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P51B-1426
Mathematics
Logic
[0720] Cryosphere / Glaciers, [5416] Planetary Sciences: Solid Surface Planets / Glaciation, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing
Scientific paper
Geologic features on the surface of Mars show clear evidence of modification by water and water ice at various intervals in the planet’s history. Several studies have demonstrated that buried water ice most likely remains today beneath tens of centimeters of soil. Past obliquity variations are theorized to have promoted the formation and stability of ground ice near the equator, allowing the accumulation of glaciers in the midlatitudes. Potential glacial features, such as lobate debris aprons (LDA) and hourglass craters containing flow features, have also been observed on the eastern rim of Hellas Basin, ranging from latitudes of 30°S to 60°S. LDAs originate at the base of steep massifs and are characterized by lobes of gently sloping, convex-upward surfaces with relatively steep outer margins. The flow-like morphology of these features, including radial and concentric lineations, suggest these features were formed by viscous flow processes. A study targeting the Hellas LDAs by the shallow radar (SHARAD) instrument aboard the Mars Reconnaissance Orbiter (MRO) returned results consistent with massive ice deposits, supporting the hypothesis that these are debris-covered glaciers. These probable glaciers are most likely large reservoirs of present-day, near-surface ice, with implications for global hydrologic cycle modeling, astrobiology studies, and the search for resources in the Solar System. Terrestrial glaciology uses the hypsometric curve, or the empirical cumulative distribution function of elevations, as one method to evaluate parameters such as equilibrium line altitude (ELA) and mass balance of a glacier. ELA is the position, or elevation, at which accumulation is balanced by ablation. Mass balance, the difference between accumulation and ablation, is crucial to the survival of a glacier over time. Both these parameters are closely related to temperature and precipitation and can thus can serve as key indicators of climate change. We apply terrestrial glaciology inventory methods to the lobate debris aprons on the eastern rim of Hellas Basin, Mars to complete a detailed volumetric inventory of the buried ice deposits and to evaluate the hypsometric curve of each feature. We then examine the relationship between LDA hypsometry and latitude in order to understand the effect of past climatic variations on present-day ice distribution. The Thermal Emission Imaging System (THEMIS) Day IR 100m Global Mosaic was used as a base map to determine areal extent, and Mars Orbiter Laser Altimeter (MOLA) data was used to ascertain elevations. Initial results show that, at latitudes at or greater than 45°S, LDAs exhibit hypsometric curves similar to classic terrestrial alpine glaciers - that is, the curve is steep at the upper and lower boundaries, and flattens in the midsection. This type of curve is indicative of a typical glacier with both accumulation and ablation zones, and could potentially be used to determine the - probably defunct - ELA of a lobate debris apron. LDAs at latitudes closer to the equator exhibit atypical hypsometric curves. This change in hypsometry with latitude potentially signals a past shift in temperature and precipitation dependent on latitude.
Christensen Per Rex
Rutledge A. M.
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