Other
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p31c0220c&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #P31C-0220
Other
5419 Hydrology And Fluvial Processes, 5464 Remote Sensing, 5470 Surface Materials And Properties
Scientific paper
Epithermal neutron flux data received from the Neutron Spectrometer, part of the Gamma Ray Spectrometer suite on board NASA's Mars Odyssey, indicates elevated equatorial hydrogen deposits partially encircle the Schiaparelli Basin. Deconvolution of the hydrogen signal statistically increased the resolution over the spectrometer's original 600 km footprint. The resulting map of hydrogen concentrations was further refined by ignoring all data <8.9% Water Equivalent Hydrogen (WEH). In so doing, this study provides the most detailed map to date of the hydrogen concentration maxima in this region and serves as a guide for future exploration. Projecting the Eastern Equatorial Hydrogen map onto the digital elevation model for the Schiaparelli Basin reveals several areas of interest. For simplification, these areas are identified by clock position relative to Schiaparelli. At the twelve o'clock position, a maximum exceeding 10% WEH occupies the upper, northern slope of a saddle between Henry Crater and unnamed craters west of Henry. Viking images of the nameless craters demonstrate wind streaks from the north veer to the southwest here, following topography. Surface drainage channels are apparent on the slope below the local WEH maximum. The 2:30 maximum lies over Tuscaloosa Crater and Verde Vallis. This >10% WEH maximum has the greatest aerial extent, roughly 200 km in diameter. At 5 o'clock, the fringing range adjacent to Brazos Valles lies within the surficially dark region called Sinus Sabaeus. It should be noted that projection of the albedo map over the terrain 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 WEH concentration as the signal's local maximum, about 10.2%, crosses areas of high and low albedo without an increase or decrease in signal strength. At 6 o'clock, two 10.4% WEH maxima line the north-facing slope of another mountain range. Both maxima are elongated, east to west. The maximum at the top of the peak overlaps the cirque-like bowl of an unnamed, degraded crater. Below the collapsed north wall of this crater sits another maximum, 100 km long by 50 km wide. The eastern end of this lower maximum contains a crater with a 6 km wide, 40 km long drainage channel leading out of the crater and down the slope toward Schiaparelli. The final WEH maximum, at 6:30, is 150 km wide by 180 km long and is centered over Evros Vallis. The maximum extends beyond Sabaeus into Noachis Terra without visibly increasing or decreasing at the albedo boundary. From this study it is clear that albedo features do not control the hydrogen signal. WEH concentrations were found both within and outside Sabaeus. It is also apparent that drainage channels are present near each maximum. This proximity may implicate areas of high WEH as the source of channel-carving fluids. Finally, WEH is not tied to a specific stratigraphic layer. The locations of the maxima can be grouped into north-facing slopes, both peaks and saddles, and broad plains containing well-developed drainage systems flowing away from the WEH maxima. 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 signals in low plains may be related to subsequent drainage when temperatures were warm enough to permit flow without immediate sublimation.
Clevy J. R.
Elphic Richard C.
Feldman William C.
Kattenhorn Simon A.
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