• Quantitative organic and light-element analysis of comet 81P/Wild 2 particles using C-, N-, and O-μ-XANES

      Cody, G. D.; Ade, H.; Alexander, C. M. O'D.; Araki, T.; Butterworth, A.; Fleckenstein, H.; Flynn, G.; Gilles, M. K.; Jacobsen, C.; Kilcoyne, A. L. D.; et al. (The Meteoritical Society, 2008-01-01)
      Synchrotron-based soft X-ray micro-analysis was performed on particles extracted from the Stardust aerogel collector in order to obtain detailed organic functional group information on any organic solids captured as part of the Principal Examination suite of analyses for samples from comet 81P/Wild 2. It is observed that cometary organic carbon captured in aerogel is present in a number of different manifestations and often intimately associated with silicates. Carbon X-ray absorption near edge structure (XANES) spectra reveal considerable chemical complexity in all of the organic particles studied so far. Universally, the comet 81P/Wild 2 organic particles contain low concentrations of aromatic and/or olefinic carbon relative to aliphatic and heteroatom-containing functional groups, e.g., amide, carboxyl, and alcohol/ethers. N-XANES confirms the presence and assignments of these functional groups. In general, the XANES data record considerable chemical complexity across the range of organic samples currently analyzed. The atomic ratios, N/C and O/C, derived from XANES data reveal a wide range in heteroatom content; in all cases these elemental ratios are higher than that of primitive meteoritic organic matter. The wide range in chemistry, both in elemental abundances and specific organic functional groups, suggests that the comet 81P/Wild 2 organic solids may have multiple origins.
    • Smelting of Fe-bearing glass during hypervelocity capture in aerogel

      Marcus, M. A.; Fakra, S.; Westphal, A. J.; Snead, C. J.; Keller, L. P.; Kearsley, A.; Burchell, M. J. (The Meteoritical Society, 2008-01-01)
      Hypervelocity capture of material in aerogel can expose particles to high transient temperatures. We tested some of the possible effects of capture by using a light-gas gun to shoot particles of basalt glass into aerogel at 6.1 km s^(-1). Using synchrotron-based micro-X-ray absorption spectroscopy (micro-XAS), we find that the starting material, in which the Fe was trivalent, is chemically reduced to divalent. In addition, some fragments were chemically reduced so that they contained Fe0 in a form spectroscopically consistent with a mixture of two forms of iron carbide (cohenite and haxonite). The carbon presumably originated from organic impurities in the aerogel. High-resolution transmission electron microscopy (HRTEM) imaging shows the presence of Fe-rich crystalline nanoparticles. A similar species has been found in actual Stardust material, suggesting that smelting effects occurred during capture and should be taken into account when interpreting data on Stardust samples.