HR: 16:15h
AN: P14A-02    [Abstracts]
TI: Estimating the Absolute Water Content of Arabia Terra Using Mars Express OMEGA Data
AU: * Milliken, R E
EM: Ralph_Milliken@brown.edu
AF: Brown University, Dept. Geological Sciences Box 1846, Providence, RI 02912 United States
AU: Mustard, J F
EM: John_Mustard@brown.edu
AF: Brown University, Dept. Geological Sciences Box 1846, Providence, RI 02912 United States
AU: Poulet, F
EM: francois.poulet@ias.u-psud.fr
AF: Institut d'Astrophysique Spatiale, Batiment 121, Orsay, 91405 France
AU: Bibring, J
EM: jean-pierre.bibring@ias.u-psud.fr
AF: Institut d'Astrophysique Spatiale, Batiment 121, Orsay, 91405 France
AU: Langevin, Y
EM: yves.langevin@ias.u-psud.fr
AF: Institut d'Astrophysique Spatiale, Batiment 121, Orsay, 91405 France
AB: High-resolution VIS-NIR data from the Mars Express OMEGA spectrometer reveal that the strength of water absorptions in the 3 um region are variable over much of Mars. Mars Odyssey GRS data also suggest the water content of the upper 1-2 m of the surface is highly variable and may contain as much as 6-10 wt. % H2O in equatorial regions such as Arabia Terra. We have applied a laboratory-derived spectral parameter, normalized optical path length (NOPL), to OMEGA reflectance spectra in order to estimate the absolute water content of the martian surface in Arabia Terra. The NOPL parameter was derived using laboratory data for several hydrated mineral species and is capable of estimating absolute water content within +/- 1 wt. %, independent of composition, when applied to the 3 um band. Previously reported areas of increased hydration (e.g., deposits in Mawrth Vallis and Valles Marineris) are characterized by the presence of an overtone water band near 1.9 - 2.1 um as well as metal-OH absorptions between 2.2 - 2.3 um, which are useful for identifying specific hydrated mineral species. Unlike those deposits, however, areas of increased hydration in Arabia do not typically exhibit statistically significant absorptions within the 1-2.5 um range. In particular, the floors and/or walls of several craters in Arabia Terra have a strong 3 um band and estimated water contents on the order of 5-10 wt. %, significantly greater than the amount of water typically observed (0.5 - 4.5 wt. %). The lack of diagnostic absorptions, however, makes it difficult to identify the host mineral for the water. Areas within these craters are often 2-3 times more hydrated than materials of similar albedo within the same OMEGA observation, indicating the increased spectral signature is not a systematic effect related to albedo or atmospheric conditions. Many of the hydrated areas occur at or near the base of central mounds within the craters. MOC and THEMIS images reveal that these mounds are commonly composed of layered materials and covered with dust, but are eroding to produce a debris cover at their base. It is the less-dusty eroded material, and not the mounds themselves, that yield the largest hydration signatures. In other cases, light-toned layered materials in the crater walls or small mesas along the outer edge of the crater floors are the source of the increased hydration signature. The morphology of these terrains is similar to those of sulfate and clay-rich deposits observed elsewhere on the planet by OMEGA. Though the OMEGA data do not show an increased hydration level for the region as a whole, the presence of hydrated materials along exposed crater walls or within eroding layered deposits suggests these materials may be pervasive through Arabia but are covered by dust or shallowly buried, only visible to OMEGA where this cover has been removed.
DE: 5419 Hydrology and fluvial processes
DE: 5460 Physical properties of materials
DE: 5464 Remote sensing
DE: 5470 Surface materials and properties
DE: 5494 Instruments and techniques
SC: Planetary Sciences [P]
MN: Fall Meeting 2005