Composition of Meridiani Hematite-rich Spherules: A Mass-Balance Mixing-Model Approach

One of the great surprises of the Mars Exploration Rovers (MER) mission is the discovery at Meridiani Planum that the surface hematite signature observed from orbit is attributable largely to a surface enrichment of hematite-rich spherules, thought to be concretions, that have weathered out of rocks similar to the underlying sulfate-rich rock formation [1]. A strong hematite signature has been observed by the Mini-TES [2] and by in-situ measurements of spherule-rich targets by the Mossbauer spectrometer (MB) [3] and the alpha-particle X-ray spectrometer (APXS) [4]. The Mini-TES derived spectrum of spherule-rich targets on the plains is consistent with nearly pure coarse-grained hematite, with perhaps as little as 5-10 areal % of other components [2]. The occurrence and abundance of the spherules as the bearer of the widespread hematite signature observed by MGS TES over much of Meridiani Planum is significant for global remote sensing, and their occurrence as concretions in the outcrop lithology is significant for the diagenetic history and role of water in the formation of the sedimentary rock formation [5].