Mössbauer spectroscopy on Mars: goethite in the Columbia Hills at Gusev crater

Abstract

In January 2004 the USA space agency NASA landed two rovers on the surface of Mars, both carrying the Mainz Mössbauer spectrometer MIMOS II. The instrument on the Mars-Exploration-Rover (MER) Spirit analyzed soils and rocks on the plains and in the Columbia Hills of Gusev crater landing site on Mars. The surface material in the plains have an olivine basaltic signature suggesting physical rather than chemical weathering processes present in the plains. The Mössbauer signature for the Columbia Hills surface material is very different ranging from nearly unaltered material to highly altered material. Some of the rocks, in particular a rock named Clovis, contain a significant amount of the Fe oxyhydroxide goethite, α-FeOOH, which is mineralogical evidence for aqueous processes because it is formed only under aqueous conditions. In this paper we describe the analysis of these data using hyperfine field distributions (HFD) and discuss the results in comparison to terrestrial analogues.