Chemical and Mineralogical Analysis of an Extraterrestrial Particle in Aerogel

Introduction: The NASA Stardust mission is expected to collect in low-density, silica aerogel more than 1,000 dust particles >10 μm in size from the dust coma surrounding Comet Wild-2. It is planned that Stardust will return these samples to Earth early in 2006. Removal of each particle from the aerogel increases the possibility of contamination or loss, thus we are developing a facility to perform in-situ chemical and mineralogical classification of particles while they are still in the aerogel. To do this, we are enhancing the x-ray-microprobe on Beamline X26A of the National Synchrotron Light Source (Brookhaven National Laboratory) to perform a variety of in-situ analyses on the Stardust returned samples, including: • X-ray Fluorescence Chemical Analyses of ~10 μm Particles, • X-Ray Diffraction Mineralogical Characterization of ~10 μm Particles. • Oxidation States by X-ray Absorption Near-Edge Structure (XANES) spectroscopy of ~10 μm particles, • Chemical Analyses of Fragments and Volatiles Deposited Along the Entry Track, • Spatial Distribution and Location of ~10 μm Particles, and, • 3-D Mapping of Individual Particle Fragmentation Fields by Computed Microtomography. As part of this instrument development effort we are analyzing a variety of particles captured in aerogel. Samples and Techniques: We examined two aerogel “keystones” which had been extracted from aerogel collectors using the methods described in a companion paper in these proceedings (Westphal et al., 2002). One keystone was extracted from the ODCE collector flown on MIR [1], and contained the complete impact event (track and terminal residue). An image of the keystone is shown in Fig. 4 of the companion paper. The terminal particle (2DO3No.1) is ~8.5 μm in diameter, located at the end of a 1,300 micron long track. The other keystone was extracted from aerogel shot with powdered ALH83100, a CM2 chondrite, at the NASA Ames Vertical Gun Range. We used the x-ray microprobe to measure the chemical compositions of 2DO3No.1 and one fragment of ALH83100 in aerogel. In each case we 0 0.2 0.4 0.6 0.8 1 1.2