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The miniaturized Mossbauer spectrometer MIMOS II is an off-the-shelf instrument, which has been successfully deployed during NASA's Mars Exploration Rover (MER) mission and was on-board the ESA/UK Beagle 2 Mars lander and the Russian Phobos-Grunt sample return mission. We propose to use a fully-qualified flight-spare MIMOS II instrument available from these missions for in situ asteroid characterization with the Asteroid Redirect Robotic Mission (ARRM).

Phosphorus is an essential element in terrestrial organisms and thus characterizing the occurrences of phosphate phases at the martian surface is crucial in the assessment of habitability. The Alpha Particle X-Ray Spectrometers onboard Spirit, Opportunity and Curiosity discovered a variety of primary and secondary phosphate phases allowing direct comparisons across the three landing sites. The Spirit rover at Gusev Crater encountered the "Wishstone/Watchtower" class of P-rich (up to 5.2 wt% P2O5) rocks interpreted to be alkaline volcanic rocks with a physical admixture of approximately 10 to 20% merrillite [Usui et al 2008]. These rocks are characterized by elevated Ti and Y and anomalously low Cr and Ni, which could largely reflect the nature of the protoliths: Evolved magmatic rocks. Many of these chemical signatures are also found in pyroclastic deposits at nearby "Home Plate" and in phosphate precipitates derived from fluid interactions with these rocks ("Paso Robles" soils). The Opportunity rover at Meridiani Planum recently analyzed approximately 4 cm clast in a fine-grained matrix, one of numerous rocks of similar appearance at the rim of Endeavour Crater. This clast, "Sarcobatus," has minor enrichments in Ca and P relative to the matrix, and like the P-rich rocks at Gusev, Sarcobatus also shows elevated Al and Ti. On the same segment of the Endeavour rim, subsurface samples were found with exceptional levels of Mn (approximately 3.5 wt% MnO). These secondary and likely aqueous deposits contain strong evidence for associated Mg-sulfate and Ca-phosphate phases. Finally, the Curiosity traverse at Gale crater encountered P-rich rocks compositionally comparable to Wishstone at Gusev, including elevated Y. Phosphorous-rich rocks with similar chemical characteristics are prevalent on Mars, and the trace and minor element signatures provide constraints on whether these are primary deposits, secondary products of physical weathering or secondary products of chemical weathering.

The mineralogical and elemental compositions of the martian soil are indicators of chemical and physical weathering processes. Using data from the Mars Exploration Rovers, we show that bright dust deposits on opposite sides of the planet are part of a global unit and not dominated by the composition of local rocks. Dark soil deposits at both sites have similar basaltic mineralogies, and could reflect either a global component or the general similarity in the compositions of the rocks from which they were derived. Increased levels of bromine are consistent with mobilization of soluble salts by thin films of liquid water, but the presence of olivine in analysed soil samples indicates that the extent of aqueous alteration of soils has been limited. Nickel abundances are enhanced at the immediate surface and indicate that the upper few millimetres of soil could contain up to one per cent meteoritic material.