September 22, 2006

AEXS is an in situ instrument for the determination of surface elemental composition using energy-dispersive XRF analysis, of samples in planetary atmosphere with no or little sample preparation. AEXS is being developed at JPL funded by the Mars Instrument Development Project (MIDP), and element of the Base Technology Program.

The AEXS instrument was used to determine elemental composition for several mineral standards in simulated atmospheres in the environmental chamber with a good agreement (4%) obtained for samples in up to 90Torr-cm thick atmosphere. The AEXS was also used to resolve composition of grains in Gabbro (Norite) sample from the Stillwater Complex, Sweet Grass County Montana, with 1.5 mm spatial resolution. Specifically, as the attached slide shows, Mg & Fe rich areas were differentiated from Ca & Al rich areas. This is the first demonstration of the ability of an XRF instrument to differentiate mineral grains by elemental composition measurements with better than several cm-scale spatial resolution. Other implemented XRF instruments (APXS, flown on MER) or the CheMin (selected for MSL mission) are essentially bulk analysis instruments. Resolving the elemental composition spatially may give clues about samples geological origin.