Author name: Penelope L. King

Sulfur on Mars

The sulfur cycle is arguably the most important geochemical cycle on Mars because the transfer of sulfur places limits on Mars’s differentiation processes, sedimentary, geomorphic and aqueous processes, past climate, and current and past habitability. The presence of sulfur-rich compositions on Mars is suggested by meteorite data, in situ bulk chemical and mineralogical analyses, remote sensing data from dust and surfaces, and geochemical models. The inferred sulfur-rich nature of Mars may have resulted in an Fe–(Ni–)S core that has been liquid throughout Mars’s history. On the surface, Mg- and Ca-sulfates are widespread and Fe3+-sulfates are found locally. It is likely that these minerals occur in a variety of hydration states and host much of the mineral-bound hydrogen in the Martian subsurface.

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Evidence for Water at Meridiani

The Mars Exploration Rover Opportunity has examined sedimentary structures in the Burns formation at Meridiani Planum. The materials in this formation reflect, in part, subaqueous deposition of reworked, sulfate-rich, clastic sediments that likely formed in a playa–interdune setting. The chemistry and mineralogy of the sedimentary rocks record an origin by evaporation of sulfate- and chloride-rich brines mixed with a fine, altered, basaltic mud or dust component, prior to reworking. Cementation and postde- positional reactions to form hematite-rich concretions and crystal-mold porosity reflect diagenesis in a groundwater-saturated subsurface. More recent dehy- dration events are evidenced by polygonal textures in rocks within craters and exposed on the plains. The timing of formation of fracture fillings that cut across bedding is not well constrained and may be early postdiagenetic or later. The fracture fillings may have formed by solutions remobilized along zones of weakness. Alteration rinds may reflect more recent interactions between rock and atmospheric water vapor.

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