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Project Progress

The bulk composition of Mars, including its total inventory of water, is central to understanding how Mars and the other inner planets formed. Comparison between the abundances of water and volatile elements in Mars, Earth, and Moon are particularly important to understand the source of water to the Earth. Martian bulk composition is also crucial to elucidating the processes involved in the initial differentiation into core, mantle and crust, and to the subsequent geologic evolution of the crust. Unraveling and quantifying the details of aqueous alteration on Mars is central to assessing the planet’s habitability and much of its geologic evolution. It also bears on determining Martian bulk composition and the source of planetesimals that accreted to form Mars.

We have continued our extensive study of aqueous alteration products in Martian meteorites, including direct measurements of D/H in weathered areas. The goal is to develop criteria for distinguishing terrestrial from Martian weathering, to define the compositions of water solutions on Mars, and to determine the D/H in bulk Mars. So far we have made detailed studies of weathering veins in the Antarctic nakhlite MIL 03346 and four new specimens of the same meteorite. Detailed study of the samples shows that they are all definitely from the same fall, so provide new opportunities to study Martian weathering and to distinguish Martian from superimposed weathering on Earth. Our dataset, along with those of previous studies, indicates the Martian fluid which flowed through MIL 03346 had a composition largely controlled by the weathering of basalt. Fluid heterogeneity was caused by a strong dependency upon the surrounding microenvironment. We have also made D/H measurements on the mineral apatite. Using criteria developed from our work on aqueous alteration, we identified apatite crystals that are almost certainly igneous, and unaltered after they formed. These grains contain water from the Martian interior, hence give direct evidence about the D/H of the martian mantle. Our initial results indicate that the martian interior has D/H similar to terrestrial mean ocean water, suggesting similar sources of water to both planets.