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A Preliminary Light Noble Gas Investigation of Stardust Samples

We have measured the concentrations and isotopic compositions of helium and neon by stepwise pyrolysis in four different Stardust sample types: (a) melted aerogel with embedded particle fragments from the track 41 wall; (b) aerogel adjacent to track 41 without visible particle fragments; (c) individual terminal particles extracted from track 108; (d) " blank " surface aerogel from cell 41. All samples were loaded in platinum foil and analyzed by procedures similar to those described in [1].0,0) were from cross sectional slices of melted track wall previously analyzed lengthwise [1]. Comparisons with results from these previous samples indicate that noble gases are distributed highly heterogeneously, with 4 He and 20 Ne concentrations significantly less than earlier measurements. Also, unlike previous pyrolyses where gas release did not occur until T > 1250 °C, in these analyses gas release peaked at ~1000 °C. The Ne-Q composition reported earlier [1] was not observed. (b) Three samples of aerogel without visible tracks or particle fragments were excavated from cell 2044 adjacent to track 41. One of these samples (#1) released sufficient helium and neon at T < 900 °C for multiple stepwise heating analyses, yielding an integrated isotopic composition of 3 He/ 4 He = (3.56 ± 0.23) x 10-4 , 20 Ne/ 22 Ne = 11.67 ± 0.62 and 21 Ne/ 22 Ne = 0.0261 ± 0.0050 that is intermediate between the Q-like composition observed previously [1] and solar wind. Another sample (#2) released extraordinarily high abundances of helium and neon between 800 and 900 °C, accompanied by very large amounts of water and hydrocarbons. High pressure induced gas release in the mass spectrometer produced a memory effect that only allows limits to be placed on the helium and neon isotopic compositions observed; nonetheless, these limits, 3 He/ 4 He < 2.2 x 10-4 and 20 Ne/ 22 Ne > 18, are intriguing in light of elevated 20 Ne/ 22 Ne ratios also seen in IDPs that may have originated in comet Grigg-Skjellerup [2]. (c) We analyzed three ~10-15 μm diameter terminal particles from track 108, C2081. Helium and neon concentrations released by stepped heating were below those seen in track 41 wall samples [1] by factors of 10 3-10 4. Detection of 20 Ne but no 22 Ne above background in one particle suggests a high 20 Ne/ 22 Ne ratio. The other two particles had no detectable neon at all. Gas …