12 Application of Modern Techniques to Address Fundamental Problems in Planetary Geology

Thursday, 2 April 2009
1:00 PM - 5:00 PM

APPLICATION OF SYNCHROTRON X-RAY FLUORESCENCE TECHNIQUES TO DISCRIMINATE AND QUANTIFY IMPLANTED SOLAR WIND IN GENESIS COLLECTORS AND IN SITU APOLLO 16 AND 17 PLAGIOCLASE GRAINS

Paper number: 12-1
Program: Symposia Sessions
Time: 1:00 PM – 1:20 PM

Authors

Abstract

Accurate knowledge of the composition of the Sun provides a baseline, which allows an understanding of how the solar system has evolved over time and how solar processes and solar wind mechanics behave. Unfortunately, the errors in photospheric abundances are too large for many planetary science problems and this hampers our understanding of these different processes. Analyses of solar wind implanted in meteorites or lunar soils have provided more precise data but the extent to which alteration processes on these bodies complicate such information is still being determined. To avoid these unknowns, NASA launched the Genesis Return Mission to obtain pristine solar wind samples. Unfortunately, the probe crash-landed shattering the 300 collector plates into 15,000+ shards and contaminating them with terrestrial fines. Therefore, in order to deal with both the surface contamination on the Genesis collector shards and the surface alteration of exposed lunar soil grains, new analytical techniques and equipment were developed and optimized at the Advanced Photon Source (GSECARS sector 13) at Argonne National Laboratory.

Specifically, in the case of the Genesis samples, the reduced size and terrestrial contamination on the surface of the collector plates necessitated the development and optimization of an angle-resolved, grazing incidence x-ray fluorescence technique. Using this technique, the elemental depth distribution was obtained resulting in the determination of absolute solar wind elemental abundances for several transition metals. We describe this application and present the solar wind Fe, Cr and Mn abundance determinations.

In the case of implanted solar wind in individual lunar soil grains, the method is based on in situ abundance measurements via microbeam x-ray fluorescence in both the implantation zone and bulk grains using the synchrotron x-ray microprobe. We describe this application and present the relative abundances of the transition metals Cr, Mn, Fe and Ni in the solar wind implanted in individual Apollo16 and 17 plagioclase grains. We relate these measurements directly to those provided by the Genesis collectors.