Other
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja....13950p&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #13950
Other
Scientific paper
To help address the questions of the nature of the low albedo regions in Valles Marineris (see Mangold et al., this meeting), we revisited the composition of these regions by modeling ISM spectra. The spectra are characterized by 1- and 2-micron absorptions diagnostic of pyroxenes, albedo (with aerosols and Minnaert corrections) lower than 15% and weak red slope between 0.8 and 2.5 μm. To reproduce these spectral characteristics, the transfer radiative theory of Shkuratov is used. The strength of this modeling method is to aid in determining appropriate end-members as well as their abundance, their grain size, and the type of mixtures (sand/dust). Low- and high-calcium pyroxenes were included in the scattering calculations. Spectrally featureless low albedo component in near-infrared to lower the average spectral reflectance is required. Oxides such as magnetite display this behavior. Hematite (a ferric oxide) was also considered because of its low albedo and its 0.85 micron absorption. Other minerals such as common amphiboles, obsidians and phyllosilicates were included in some scattering calculations, but we showed that these different minerals are unlikely because of the frustating lack of diagnostic features other than due to pyroxene. Other common minerals with weaker absorptions such as feldspar and olivine were considered. Three types of surface were investigated: dust (mixture of particles of size << wavelength), sand (intimate mixture of particles of size >> wavelength), dust/sand mixture. The best fits of the entire 0.8-2.5 micron spectra are obtained with a mixture of five components: a four-components intimate mixture of low- (<20%) and high-calcium (<30%) pyroxenes, olivine (<10%), and hematite (10%) mixed with a large proportion of dusty grains of hematite and magnetite (about 55%). There is no significant difference of composition between the different spectra. This suggests that most rocks units are similar in composition, hidden by homogenized surface materials, or some combination of both.
Erard Stephane
Mangold Nicolas
Poulet François
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