Investigation of the Near-Infrared Spectral Characteristics of Massive Analog Materials for Igneous Martian Crust.

Abstract

All the spectra that have been obtained from Mars to date are dominated by features of the regolith that covers the surface. This leads to difficulties in retrieving useful information from the spectra about the unweatheres igneous crust that lies underneath. The visible and infrared mapping spectrometer Omega on board of the Russian Mars 96 spacecraft would have had a spatial resolution high enough (up to 500 m) to obtain spectra from objects with a much lower coverage by regolith than is common for the Martian surface (e.g. the canyon walls of Valles Marineris). Should Omega, or equally powerful mapping spectrometers, be launched to Mars in future missions, laboratory investigations of massive analog materials will be neccessary to facilitate the interpretation of spectra dominated by features of outcropping rock of igneous Martian crust. So far, most of the reflectance spectroscopy investigations of Martian analog materials have been done with powdered samples. Nevertheless, it is known fact that there are differences in the spectral characteristics of a massive sample change with the surface roughness. In this study, powders and slabs of the same mineral and rock specimens were prepared (three different pyroxenes and three different basalts); of all samples, reflectance spectra were recorded in the near-infrared (0.7 to 5 µm), to compare the differences in the spectral characteristics of the powders and the slabs. Furthermore, the roughness of the slabs was systematically altered by grinding and polishing, in order to investigate the dependence of the spectral features on the condition of the surface.