• Carbon investigation of two Stardust particles: A TEM, NanoSIMS, and XANES study

      Matrajt, G.; Ito, M.; Wirick, S.; Messenger, S.; Brownlee, D. E.; Joswiak, D.; Flynn, G.; Sandford, S.; Snead, C.; Westphal, A. (The Meteoritical Society, 2008-01-01)
      In this work we present the results of a systematic search for cometary organics in 14 Stardust particles (particles from comet 81P/Wild 2, captured by NASAs Stardust mission) by TEM and multidisciplinary studies (XANES and NanoSIMS) of Febo and Ada, two of the organic-bearing particles identified. The combination of the three analytical techniques has established the presence of organic, cometary degrees C in both particles. Using energy-filtered and high-resolution imaging it was shown that the degrees C is amorphous and rare, given that it is found in grains less than or equal to 200 nm in size that are not abundant throughout the particles. The XANES maps and spectra of the carbonaceous areas identified with the TEM have shown that the carbonaceous material is organic due to the presence of carbonyl (C=O) functional groups and the overlapping of degrees C and N on the same grains. In addition, several different C-XANES spectra were obtained from the same particle, suggesting that there is diversity in the types of carbonaceous phases present in these particles, as well as a heterogeneous distribution of the carbonaceous phases within these particles. The C-XANES spectra obtained are different from C-XANES spectra of carbonaceous chondrites and IDPs. In the particle Febo we found five spots showing a pronounced enrichment in the isotope 15N (delta-15N from 420 to 639 +/- 20 to 70 ppm, 1-sigma) that were clearly associated with the C-rich regions. The carbonaceous material has approximately solar C and D/H isotopic compositions, and the bulk O isotopic composition was found to be delta-17O = -18 +/- 13 ppm and delta-18O = -37 +/- 12 ppm (1-sigma). In the particle Ada we found a C-rich phase with enrichments in the isotope 15N (delta-15N = 550 +/- 70 ppm, 1-sigma) and the isotope D (delta-D = 610 +/- 254 ppm, 1-sigma). The C isotopic composition at this phase is solar (delta-13C = -4 +/-29 ppm, 1 sigma). The bulk O isotopic composition of Ada was found to be delta-17O = 9 +/- 14.6 ppm and delta-18O = -7.3 +/- 8.1 ppm (2-sigma).
    • Characteristics of cometary dust tracks in Stardust aerogel and laboratory calibrations

      Burchell, M. J.; Fairey, S. A. J.; Wozniakiewicz, P.; Brownlee, D. E.; Hörz, F.; Kearsley, A. T.; See, T. H.; Tsou, P.; Westphal, A.; Green, S. F.; et al. (The Meteoritical Society, 2008-01-01)
      The cometary tray of the NASA Stardust spacecraft’s aerogel collector was examined to study the dust captured during the 2004 flyby of comet 81P/Wild 2. An optical scan of the entire collector surface revealed 256 impact features in the aerogel (width >100 micrometers). Twenty aerogel blocks (out of a total of 132) were removed from the collector tray for a higher resolution optical scan and 186 tracks were observed (track length >50 micrometers and width >8 micrometers). The impact features were classified into three types based on their morphology. Laboratory calibrations were conducted that reproduced all three types. This work suggests that the cometary dust consisted of some cohesive, relatively strong particles as well as particles with a more friable or low cohesion matrix containing smaller strong grains. The calibrations also permitted a particle size distribution to be estimated for the cometary dust. We estimate that approximately 1200 particles bigger than 1 micrometer struck the aerogel. The cumulative size distribution of the captured particles was obtained and compared with observations made by active dust detectors during the encounter. At large sizes (>20 micrometers) all measures of the dust are compatible, but at micrometer scales and smaller discrepancies exist between the various measurement systems that may reflect structure in the dust flux (streams, clusters etc.) along with some possible instrument effects.
    • Chemical composition and heterogeneity of Wild 2 cometary particles determined by synchrotron X-ray fluorescence

      Lanzirotti, A.; Sutton, S. R.; Flynn, G. J.; Newville, M.; Rao, W. (The Meteoritical Society, 2008-01-01)
      Seven cometary dust particle tracks in Stardust aerogel were studied using synchrotron X-ray fluorescence methods at the National Synchrotron Light Source (NY) and Advanced Photon Source (IL). Elemental maps were produced for each of the tracks and elemental abundances for 156 individual fragments within these tracks were determined. Whole-track elemental abundances were inferred by summing the elemental masses for the fragments in each track and scaling by the ratio of total Fe in the map and total Fe in the fragments. In general, whole-track and terminal-particle abundances are dissimilar. The total Fe masses ranged from 4 to 2200 pg, corresponding to impactors in the size range of 2.7 to 22 micrometers if Fe abundances are equal to the chondritic value. Systematic variations in element abundance with fragment distance from the aerogel entry point were generally subtle but were pronounced in one track (C2115,19). In this track, Zn/Fe was about three orders of magnitude higher at the top, Cr/Fe was two orders of magnitude higher at the bottom, and S was relatively uniform. Compositional convergence data showed that typically analysis of ~10 fragments was needed to reach convergent whole-track abundance. Zinc was an exception, showing nonconvergent profiles and steps due to the presence of rare, high-Zn fragments. The resulting wholetrack elemental abundances show diverse patterns that are generally chondritic (i.e., within a factor of three of CI abundances) with some exceptions, notably depletions in S and enrichments in the moderately volatile elements Cu, Zn, and Ga. Enrichments in large ion lithophile elements relative to Fe were observed in one track. Correlation matrices showed several strong elemental correlations, notably selenium associated with sulfur (sulfides), a ubiquitous correlation of the first-row transition metals Cr, Mn, and Fe attributed to the presence of pyroxene, and enrichments of gallium associated with calcium, likely affiliated with Mg-Al glass.
    • Combined micro-Raman, micro-infrared, and field emission scanning electron microscope analyses of comet 81P/Wild 2 particles collected by Stardust

      Rotundi, A.; Baratta, G. A.; Borg, J.; Brucato, J. R.; Busemann, H.; Colangeli, L.; D'Hendecourt, L.; Djouadi, Z.; Ferrini, G.; Franchi, I. A.; et al. (The Meteoritical Society, 2008-01-01)
      We report combined micro-infrared, micro-Raman, and field emission scanning electron microscope (FESEM) analyses of particles collected by the Stardust spacecraft during its flyby of comet 81P/Wild 2 on 2 January 2004 and successfully returned back to Earth on 15 January 2006. We present mid-infrared (IR) spectra of six of these particles. The CH2/CH3 ratios inferred from the infrared data are greater than those seen in organics in the diffuse interstellar medium, possibly indicating the presence of longer or less branched aliphatic chains. The micro-Raman data offer insights into the state of the order of the carbonaceous component present in the particles. Raman parameters for most of the particles span a similar range to that observed in interplanetary dust particles (IDPs) and the most primitive meteorites. Both the IR and Raman data imply the presence of a very labile carbonaceous component. Hydrated silicates may be present in two particles of Track 35, one of which may also contain carbonates, but further investigations with other techniques need to be performed to confirm these findings. In some cases, the analyses are difficult to interpret because of the presence of compressed aerogel mixed with the grains.
    • Curation, spacecraft recovery, and preliminary examination for the Stardust mission: A perspective from the curatorial facility

      Zolensky, Michael; Nakamura-Messenger, Keiko; Fletcher, Lisa; See, Thomas (The Meteoritical Society, 2008-01-01)
      We describe briefly some of the challenges to the Stardust mission, curation, and sample preliminary analysis from the perspective of the Curation Office at the Johnson Space Center. Our goal is to inform persons planning future sample returns so that they may learn from both our successes and challenges (and avoid some of our mistakes). The Curation Office played a role in the mission from its inception, most critically assisting in the design and implementation of the spacecraft contamination control plan, and in planning and documenting the recovery of the spacecraft re-entry capsule in Utah. A unique class 100 cleanroom was built to maintain the returned comet and interstellar samples in clean comfort, and to permit dissection and allocation of samples for analysis.
    • Dust from comet Wild 2: Interpreting particle size, shape, structure, and composition from impact features on the Stardust aluminum foils

      Kearsley, A. T.; Borg, J.; Graham, G. A.; Burchell, M. J.; Cole, M. J.; Leroux, H.; Bridges, J. C.; Hörz, F.; Wozniakiewicz, P. J.; Bland, P. A.; et al. (The Meteoritical Society, 2008-01-01)
      Aluminum foils of the Stardust cometary dust collector are peppered with impact features of a wide range of sizes and shapes. By comparison to laboratory shots of known particle dimensions and density, using the same velocity and incidence geometry as the Stardust Wild 2 encounter, we can derive size and mass of the cometary dust grains. Using scanning electron microscopy (SEM) of foil samples (both flown on the mission and impacted in the laboratory) we have recognized a range of impact feature shapes from which we interpret particle density and internal structure. We have documented composition of crater residues, including stoichiometric material in 3 of 7 larger craters,by energy dispersive X-ray microanalysis. Wild 2 dust grains include coarse (>10 micrometers) mafic silicate grains, some dominated by a single mineral species of density around 34 g cm^(-3) (such as olivine). Other grains were porous, low-density aggregates from a few nanometers to 100 micrometers, with an overall density that may be lower than 1 g cm^(-3), containing mixtures of silicates and sulfides and possibly both alkali-rich and mafic glass. The mineral assemblage is very similar to the most common species reported from aerogel tracks. In one large aggregate crater, the combined diverse residue composition is similar to CI chondrites. The foils are a unique collecting substrate, revealing that the most abundant Wild 2 dust grains were of sub-micrometer size and of complex internal structure. Impact residues in Stardust foil craters will be a valuable resource for future analyses of cometary dust.
    • Identification of mineral impactors in hypervelocity impact craters in aluminum by Raman spectroscopy of residues

      Burchell, M. J.; Foster, N. J.; Kearsley, A. T.; Creighton, J. A. (The Meteoritical Society, 2008-01-01)
      Here we demonstrate the use of Raman spectroscopy techniques to identify mineral particle fragments after their impact into aluminum foil at ~6 km s^(-1). Samples of six minerals (olivine, rhodonite, enstatite, diopside, wollastonite, and lizardite) were fired into aluminum foil and the resulting impact craters were studied with a HeNe laser connected to a Raman spectrometer. Raman spectra similar to those of the raw mineral grains were obtained from the craters for impacts by olivine, rhodonite, enstatite, wollastonite, and diopside, but no Raman signals were found from lizardite after impact. In general, the impactors do not survive completely intact, but are fragmented into smaller fractions that retain the structure of the original body. Combined with evidence for SEM and FIB studies, this suggests that in most cases the fragments are relatively unaltered during impact. The survival of identifiable projectile fragments after impact at ~6 km s^(-1) is thus established in general, but may not apply to all minerals. Where survival has occurred, the use of Raman spectroscopic techniques for identifying minerals after hypervelocity impacts into a metallic target is also demonstrated.
    • 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.
    • Recovering the elemental composition of comet Wild 2 dust in five Stardust impact tracks and terminal particles in aerogel

      Ishii, H. A.; Brennan, S.; Bradley, J. P.; Luening, K.; Ignatyev, K.; Pianetta, P. (The Meteoritical Society, 2008-01-01)
      The elemental (non-volatile) composition of five Stardust impact tracks and terminal particles left from capture of comet 81P/Wild 2 dust were mapped in a synchrotron X-ray scanning microprobe with full fluorescence spectra at each pixel. Because aerogel includes background levels of several elements of interest, we employ a novel "dual threshold" approach to discriminate against background contaminants: an upper threshold, above which a spectrum contains cometary material plus aerogel and a lower threshold below which it contains only aerogel. The difference between normalized cometary-plus-background and background-only spectra is attributable to cometary material. The few spectra in-between are discarded since misallocation is detrimental: cometary material incorrectly placed in the background spectrum is later subtracted from the cometary spectrum, doubling the loss of reportable cometary material. This approach improves accuracy of composition quantification. We present the refined whole impact track and terminal particle elemental abundances for the five impact tracks. One track shows mass increases in Cr and Mn (1.4x), Cu, As and K (2x), Zn (4x), and total mass (13%) by dual thresholds compared to a single threshold. Major elements Fe and Ni are not significantly affected. The additional Cr arises from cometary material containing little Fe. We exclude Au intermixed with cometary material because it is found to be a localized surface contaminant carried by comet dust into an impact track. The dual threshold technique can be used in other situations where elements of interest in a small sample embedded in a matrix are also present in the matrix itself.
    • 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.
    • TOF-SIMS analysis of cometary particles extracted from Stardust aerogel

      Stephan, T.; Flynn, G. J.; Sandford, S. A.; Zolensky, M. E. (The Meteoritical Society, 2008-01-01)
      Sections of seven cometary fragments extracted from the aerogel collector flown on the Stardust mission to comet 81P/Wild 2 were investigated with TOF-SIMS. These grains showed a rather heterogeneous chemical and mineralogical composition on a submicrometer scale. However, their average chemical composition is close to bulk CI chondritic values, which is consistent with analyses of numerous Stardust samples using various techniques. As a result, the TOF-SIMS analyses support the conclusion that Wild 2 has a CI-like bulk composition. The cometary particles resemble anhydrous chondritic porous interplanetary dust particles, which have previously been suggested to originate from comets. For one of the fragments, polycyclic aromatic hydrocarbons that could possibly be attributed to the comet were observed.
    • TOF-SIMS analysis of crater residues from Wild 2 cometary particles on Stardust aluminum foil

      Leitner, J.; Stephan, T.; Kearsley, A. T.; Hörz, F.; Flynn, G. J.; Sandford, S. A. (The Meteoritical Society, 2008-01-01)
      Impact residues of cometary particles on aluminum foils from the Stardust mission were investigated with TOF-SIMS for their elemental and organic composition. The residual matter from comet 81P/Wild 2 shows a wide compositional range, from nearly monomineralic grains to polymict aggregates. Despite the comparably small analyzed sample volume, the average element composition of the investigated residues is similar to bulk CI chondritic values. Analysis of organic components in impact residues is complicated, due to fragmentation and alteration of the compounds during the impact process and by the presence of contaminants on the aluminum foils. Nevertheless, polycyclic aromatic hydrocarbons (PAHs) that are unambiguously associated with the impact residues were observed, and thus are most likely of cometary origin.