• Characterization of carbon- and nitrogen-rich particle fragments captured from comet 81P/Wild 2

      Gallien, J.-P.; Khodja, H.; Herzog, G. F.; Taylor, S.; Koepsell, E.; Daghlian, C. P.; Flynn, G. J.; Sitnitsky, I.; Lanzirotti, A.; Sutton, S. R.; et al. (The Meteoritical Society, 2008-01-01)
      We studied three Stardust fragments with infrared spectroscopy to characterize organic matter; with synchrotron-induced X-ray fluorescence to determine Fe contents and certain elemental ratios to iron; with scanning electron microscopy (SEM) to image sample morphology and to detect semiquantitatively Mg, Al, Si, Ca, and Fe; and with nuclear reaction analysis (NRA) to measure degrees C, N, O, and Si. A fourth fragment was analyzed by SEM only. Fragment C2054,0,35,21 from track 35 (hereafter C21) is extremely rich in degrees C and contains appreciable concentrations of Mg, Al, and Ca, but little Fe. Fragments C2054,0,35,23 (C23), C2044,0,41 (C41), and C2054,0,35,51,0 (C51), from tracks 35, 41, and 35, respectively, consist largely but not exclusively of aerogel. C23 contains Mg and finely dispersed S, but little Al, Ca or Fe. Pooled CI-normalized elemental ratios for C21, C23, and C41 are as follows: Ti/Fe, 5.0; Cr/Fe, 0.84; Mn/Fe, 0.97; Ni/Fe, 2.4; and Zn/Fe, 31. The enrichments in Ti and Zn may be related to the presence of aerogel. Minimum weight percentages of degrees C and N estimated without correcting for the presence of aerogel are 30 and 0.7 for C21; 2.8 and 0.2 for C23; 1.2 and 0.14 for C41. After corrections for the presence of aerogel containing 1.4 wt% degrees C and 0.02 wt% N, the corresponding results are 37 and 0.85 for C21; and 10 and 1 for C23; and ~1 and ~1, for C41 (The results for C41 have large uncertainties). These weight percentages are larger than or comparable to values for carbonaceous meteorites. degrees C/N atomic ratios without/without aerogel corrections are 51/51 for C21, 17/11 for C23, and 10/~1 for C41. Within the uncertainties these values are within the range for carbonaceous meteorites.
    • 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.
    • TOF-SIMS analysis of cometary matter in Stardust aerogel tracks

      Stephan, T.; Rost, D.; Vicenzi, E. P.; Bullock, E. S.; MacPherson, G. J.; Westphal, A. J.; Snead, C. J.; Flynn, G. J.; Sandford, S. A.; Zolensky, M. E. (The Meteoritical Society, 2008-01-01)
      Cometary matter in aerogel samples from the Stardust mission was investigated with TOF-SIMS for its elemental and organic composition. While single grains >1 micrometer are highly variable in their chemical composition, nanometer-scale material found in the wall of one track has within a factor of 1.22 bulk CI chondritic element ratios relative to Fe for Na, Mg, Al, Ti, Cr, Mn, and Co. Compared to CI, a depletion in Ca by a factor of four and an enrichment in Ni by a factor of two was observed. These results seem to confirm recent reports of a CI-like bulk composition of Wild 2. The analysis of organic compounds in aerogel samples is complicated by the presence of contaminants in the capture medium. However, polycyclic aromatic hydrocarbons that could possibly be attributed to the comet were observed.
    • 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.