Clevy, J.R., Elphic, R.C., Kattenhorn, S.A. (2006)
Investigation of seasonal variation within the eastern equatorial hydrogen signal, Mars
Eos, Transactions of the American Geophysical Union 87(52), Fall Meeting Supplement, Abstract P23C-0079.
The Neutron Spectrometer (NS) on board NASA's Mars Odyssey has identified two mid-latitude regions of low epithermal neutron flux, which are predicted to have a high weight percent of hydrogen in the top meter of regolith. In a previous study of the Eastern Equatorial Hydrogen (EEH), centered on Schiaparelli Basin, we draped the NS signal over a digital elevation model to define the spatial extent and topographic placement of the EEH reserve. All of the available records were included in the study, producing a static, time-averaged map. A bimodal relationship between the hydrogen concentration and topography emerged with north-facing slopes and low-lying areas both showing low epithermal counts. To determine the processes driving the hydrogen accumulation it was necessary to ascertain whether these areas represented 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.
To best preserve seasonal effects, the Martian year was broken down into eight seasons, each covering 45 degrees of solar latitude (Ls), and grouped into pairs that bracket each solstice and equinox as experienced in the northern hemisphere (e.g. early and late summer are the 45 degrees before and after the summer solstice at 90° Ls). A time sequence was created using each season from each year of atmospherically corrected NS data. Preliminary investigation of the time sequence indicates that in addition to expected areas of stable low flux, there is some seasonal variability across the EEH, hinting at a mobile component in the signal as well. Topographic control of the hydrogen was apparent along the highlands separating the Schiaparelli Basin from Hellas Basin and most evident in a NE--SW trend from -11°, 49° E down to -21°, 35° E. While the EEH is roughly circular, the southeast portion, above -1100 m elevation, contains consistently higher concentrations of hydrogen. The portion below -1300 m in elevation, contains variations of 10 to 13% Water Equivalent Hydrogen (WEH), while between -1000 and 2200 m local maxima vary from 18 to 25.8% WEH.
External link: AGU database
Citations:
This abstract has been cited in the following works:
Clevy, J.R., Kattenhorn, S.A., 2008. Structural constraints on the eastern equatorial hydrogen concentration inferred from MOLA, crustal thickness, and infrared imagery. LUNAR AND PLANETARY SCIENCE CONFERENCE ABSTRACTS XXXIX: #2414.
