Geochemical tools for Mars exploration

Mars Global Surveyor carried a Thermal Emission Spectrometer (TES), which provided thermal infrared spectra. Lattice vibrations in many minerals absorb thermal energy, so the 

Various TES-derived estimates of Mars surface chemistry, based on mineral deconvolutions using different spectral libraries, were compiled by McSween et al. (2003). A subsequent spectral study identified 11 compositionally different regions on Mars (Rogers and Christensen, 2007). 

A major difference between the GRS and TES-derived chemical datasets is that y-rays penetrate and measure to 20-30 cm depth, whereas TES spectra sample only the outermost micron of surface grains. As we will see, surface alteration of rocks and soils has modified their compositions to such an extent that the TES data no longer give bulk sample chemistry, although they still provide valuable information on chemical alteration. 

The Viking landers provided X-ray fluorescence (XRF) data for a limited number of Martian soils at two landing sites. These data were compiled by Clark et al. (1982). 

The Mars Pathfinder rover carried an Alpha Proton X-ray Spectrometer (APXS), and the two Mars Exploration Rovers (MER - Spirit and Opportunity) carried Alpha Particle X-ray Spectrometers (also called APXS, but in this case more precise versions of the Pathfinder instrument, though without the ability to monitor protons for light element analyses). These instruments contained radioactive curium sources (Fig. 13.16) whose decay produced a-particles, which irradiated target rocks and soils. The resulting characteristic X-rays provided measurements of major and minor element abundances. The MER rovers also carried Mossbauer spectrometers, which yielded information on iron oxidation state. 

---