Hyperspectral imaging of sulfate evaporate deposits in Western Australia and on Mars

Abstract

The European hyperspectral imaging instrument OMEGA has been in operation around Mars since early 2004. OMEGA has constructed imaging maps covering almost the entire Martian surface (Bibring <i>et al.</i>, 2005). The OMEGA science team have identified a 60 x 200km deposit rich in Ca-sulfates, most likely gypsum, near the Martian northern polar cap (Langevin <i>et al.</i>, 2005). They have suggested an evaporation origin linked to varying Martian obliquity, warming the poles during periods of high obliquity, causing the melting of water ice, and then evaporation of this ephemeral water, leaving behind salty brines adjacent to the frozen ice cap. In 2004, a hyperspectral imaging survey of the Yilgarn Craton was carried out using the HyMap instrument (Cocks <i>et al.</i>, 1998). The Yilgarn is a good Mars analog due to the presence of ultramafic-mafic volcanic basalt flows. We have therefore analysed this hyperspectral coverage of the evaporite deposits of the Yilgarn Craton to compare an accessible, Earth-based evaporate analog with the Mars sulfate deposits. Using standard hyperspectral analysis methods, we have mapped gypsum in Western Australian dry lake evaporite deposits near Kalgoorlie. In the future, we shall use an absorption band modelling method (<i>Brown et. al.</i>, 2005) to determine the shape, position and intensity of absorption bands that are due to sulfates. Fieldwork in this area has enabled a laboratory based evaluation of hand samples of gypsum taken from the Western Australian deposits. Evaluation of this data and comparison to future Martian hyperspectral data will lead to a greater understanding of the hydration state and cation type of Martian sulfate deposits.