Clevy, J.R., Kattenhorn, S.A. (2006)
Investigation of the eastern equatorial hydrogen signal in relation to Martian topography
Proceedings of the NASA-Idaho Space Grant Consortium Research Symposium 1: 16-17.
Epithermal neutron data received from the Neutron Spectrometer (NS), part of the Gamma Ray Spectrometer suite on board NASA's Mars Odyssey, provides evidence of two mid-latitude regions of low epithermal neutron flux. These regions are predicted to have a high weight percent of hydrogen within the top meter of Martian regolith. Our work examines the Eastern Equatorial Hydrogen (EEH) which is roughly centered on Schiaparelli Basin. Four our study we relied on a map of the NS signal provided by Los Alamos National Laboratory. All of the available records were included in the study, producing a static, time-averaged map which we draped over a digital elevation model (DEM) to define the spatial extent and topographic placement of the EEH reserve. In so doing, this study provides the most detailed map to date of the hydrogen concentration maxima in this region and furthers the Science Mission Directorate by aiding in the location of hydrogen reserves in preparation for human exploration of Mars.
A bimodal relationship between the hydrogen concentration and topography emerged with north-facing slopes and low-lying areas both showing low epithermal counts (high hydrogen). The former could indicate up-slope orographic deposition of hydrogen in the form of water ice as air masses rise and cool, preferentially coating north-facing slopes. High hydrogen signals in low plains may be related to subsequent drainage when temperatures were warm enough to permit flow without immediate sublimation. Well-developed drainage channels present near the low-lying hydrogen concentrations seem to implicate the local maxima at higher elevations as the source areas of channel-carving fluids. Low lying areas also favor the accumulation of liquids which in turn favor mineral deposition.
To determine the processes driving the hydrogen accumulation it is necessary to ascertain whether these areas represent static deposits of hydrogen or seasonally variable concentrations. Certain hydrogen sources, jarosite for example, would be expected in low-lying, poorly- or slowly-drained areas. Such deposits should map out as fixed areas of low flux with little if any seasonal variation. Ito should also be noted that protection of the albedo map over the DEM reveals dark grains concentrating in low areas, presumably having moved short distances by wind and gravity. The absence or presence of these grains does not seem to affect the measured hydrogen concentration as it crosses areas of high and low albedo without an increase of decrease in signal strength.
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