Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p21a..07m&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #P21A-07
Physics
0933 Remote Sensing, 5410 Composition (1060, 3672), 5455 Origin And Evolution, 5470 Surface Materials And Properties, 6225 Mars
Scientific paper
All VIS-NIR spectra acquired by the Mars Express OMEGA spectrometer exhibit a 3 um absorption due to H2O. This feature varies in strength and shape over spatial and temporal scales, suggesting the hydration state of the near surface also varies over these dimensions. We use a laboratory-based model to relate the strength of this absorption to absolute water content (wt. % H2O) on Mars, finding that equatorial and mid- latitude zones have water contents of 2-5 wt. %, whereas hydration increases poleward of ~60° and can reach values upward of 12 %. The latter agrees qualitatively with estimates of H content from Mars Odyssey GRS data, though GRS is sensitive to a greater depth than OMEGA and observes buried ice, whereas OMEGA is observing the hydration of the uppermost fraction of the surface. The regolith at high latitudes likely holds more H2O because it seeks equilibrium between both ice at depth and water vapor in the overlying atmosphere, whereas equatorial zones do not contain buried ice. Obliquity-driven glacial cycles during the Amazonian may have formed ice-rich deposits at mid and high latitudes, a possible mechanism for increasing the H2O content of any hydrous phases present in the regolith or dust within these regions. Spectra for high latitudes and dusty regions lack spectral features indicative of specific hydrated minerals, but the presence of a 3 um feature in all OMEGA spectra and our estimates of H2O for bright regions, which are greater than the limit for surface- adsorbed H2O, suggest some fraction of hydrated material is present in the ubiquitous Mars dust. The GRS instruments also detect a large region of increased H abundance in Arabia Terra, but OMEGA spectra only detect an increase in hydration for small, relatively dust-free outcrops of high thermal inertia materials in this region. The high albedo and low thermal inertia of Arabia suggests a thin dust cover may commonly mask the presence of hydrated phases from OMEGA, thus they are only visible in small outcrops where this cover has been removed. Spectra of these outcrops do not exhibit absorptions directly attributable to OH, SO4, or CO3 groups, thus the composition of the hydrated phase is unknown. Nearby regions such as Terra Meridiani and Mawrth Vallis, however, contain hydrated sulfates and phyllosilicates. Our model estimates water contents of 6-9 wt. % for these materials, the highest observed in the equatorial regions to date. The OMEGA observations, in conjunction with GRS and MER results, suggest hydrated phases are present in the sedimentary record over vast regions of Mars, primarily within +/- 30° of the equator. Upcoming observations by Phoenix and the high-resolution CRISM spectrometer onboard MRO will likely provide additional insight into the nature of these hydrated phases.
Bibring J.
Gondet Brigitte
Jouglet Denis
Langevin Yves
Milliken Ralph E.
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