Mathematics – Logic
Scientific paper
Sep 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.5706b&link_type=abstract
American Astronomical Society, DPS meeting #41, #57.06
Mathematics
Logic
Scientific paper
The north polar region of Mars has had a complex geologic history, part of which has involved aqueous processes. A major surface unit in this region is a large (4.7 million km2), low albedo area of sand dunes/sheets (the north polar erg) spanning the circumpolar plains. We are investigating the mineralogy and geologic history of the erg using a variety of data sets, including mid-IR spectra from MGS/TES and near-IR spectra from MEx/OMEGA. The southernmost extent of this deposit extends into Acidalia Planitia, where it is the type locality for the TES "ST2" global compositional endmember. We are using TES and OMEGA data to identify the primary (mafic) mineralogy of these sand deposits, and to explore the processes and relationships between these primary minerals and previously-identified secondary alteration products in the region like polyhydrated sulfates. Our TES data subset, chosen from generally warm (> 250K), high-quality spectra taken through relatively clear atmospheric conditions, consists of several thousand emissivity spectra at latitudes above 70N. We are performing atmospheric corrections and deriving estimated mineral abundances for these spectra using a previously-developed iterative linear matrix inversion spectral unmixing method (Noe Dobrea et al., 2006: doi:10.1029/2005JE002431) and laboratory-derived mineral endmembers from the TES library. Using 68 spectrally-unique endmembers, we compute best-fit abundances for all possible endmember combinations and estimate average abundances for each mineral. Minerals not detected above a minimum detection threshold are discarded, which then allows us to converge on the most statistically accurate representation of the likely mineral assemblage. Initial results of modeling average polar erg spectra reveals an "expected" mafic assemblage (olivine, pyroxene, feldspar) plus a silica-bearing amorphous phase. "Unexpected" phases identified include Mg-, Al-, and Fe-bearing sulfates and iron oxides. Our results augment and enhance previous OMEGA findings on the aqueous mineralogy of the Martian north polar region.
Bell James F.
Horgan H. N. B.
Noe Dobrea Eldar Z.
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