Jarosite and Hematite at Meridiani Planum from Opportunity's Mössbauer Spectrometer.

Mössbauer spectrometers provide quantitative information about the distribution of iron among its oxidation states, the identification of iron-bearing phases, and the distribution of iron among those phases. Characterizing the speciation and distribution of iron in martian rock and soil [1] constrains primary rock types; the conditions under which primary minerals crystallize; and the mineralogical composition, process, and extent of alteration and weathering. Hematite (α-Fe[sub 2]O[sub 3]) was detected in Meridiani Planum from orbital observations before the Mars Exploration Rover (MER) missions [2, 3], and the region was selected as a MER landing site on a scientific basis, because the mineral is a beacon for aqueous processes, and on an engineering basis, because the terrain was considered safe for landing [4]. The first Mössbauer spectrum from Meridiani Planum was obtained by the Opportunity rover on 4 February 2004, on soil near the lander at Eagle crater. [ABSTRACT FROM AUTHOR]