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E.Z. Noe Dobrea, M.C. Malin (Malin Space Science Systems)
The process of linearly unmixing an observed spectrum relies heavily on the input spectral library, and variations in such library can often yield different, irreconcilable results [e.g., 1,2,3]. It is in part for this reason that the mineralogy of the northern lowlands of Mars, and in particular that of Acidalia Planitia, remains to this date highly controversial. Unmixing of thermal emission spectra of the region has yielded ambiguous results, where the derived mineralogies imply different past environments and geologic histories [1,2,3]. Because the resolution of this issue has the potential to provide invaluable information regarding the past history of Mars, experiments to provide additional insight into the nature of this terrain have been performed [4,5], but more work remains to be done.
We have performed searches for small scale (~km) variations in mineralogy using spectral ratio techniques on both MGS/TES and Mars Express/OMEGA data. In addition to reducing the level of systematic noise, this method allows us to identify and isolate the spectral signature of potentially diagnostic minerals whose concentration is spatially variable with respect to the background. Searches in southeastern Acidalia have revealed areas that display enhanced spectral absorptions at low wavenumbers (i.e. 200-600 cm-1) in regions that present a greater amount of mantling material in MOC/NA images. Comparison to the ASU spectral library shows that these absorptions are consistent with those of either hematite or fayalite. Further analysis of these regions using OMEGA data display an additional absorption centered at around 3.5-\mum. Whereas the shape of the spectrum and its band locations are not consistent with the spectrum of hematite, some resemblance to the 3.5-\mum band in olivine is apparent.
[1] Science 287, 1626-1630 (2000). [2] Nature 421, 711-712 (2002). [3] Nature 417, 263-266 (2002). [4] In: Sixth Int. Conf. mars, Pasadena, CA Abs.#3258 (2003). [5] Icarus 174, 161-177 (2005).
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.