A Refractory Inclusion Returned by Stardust from Comet 81P/Wild 2
Among the samples returned from comet 81P/Wild 2 by the Stardust spacecraft is a suite of particles from one impact track (Track 25) that are Ca-, Al-rich and FeO-free. We studied three particles from this track that range in size from 5.3 x 3.2 {micro}m to 15 x 10 {micro}m. Scanning and transmission electron microscopy show that they consist of very fine-grained (from {approx}0.5 to {approx}2 {micro}m) Al-rich, Ti-bearing and Ti-free clinopyroxene, Mg-Al spinel, anorthite, perovskite, and osbornite (TiN). In addition to these phases, the terminal particle, named 'Inti', also contains melilite. All of these phases, with the exception of osbornite, are common in refractory inclusions and are predicted to condense at high temperature from a gas of solar composition. Osbornite, though very rare, has also been found in meteoritic refractory inclusions, and could have formed in a region of the nebula where carbon became enriched relative to oxygen compared to solar composition. Compositions of Ti-pyroxene in Inti are similar, but not identical, to those of fassaite from Allende inclusions. Electron energy loss spectroscopy shows that Ti-rich pyroxene in Inti has Ti{sup 3+}/Ti{sup 4+} within the range of typical meteoritic fassaite, consistent with formation under reducing conditions comparable to those of a system of solar composition. Inti is {sup 16}O-rich, with {delta}{sup 18}O {approx} {delta}{sup 17}O {approx} 40{per_thousand}, like unaltered phases in refractory inclusions and refractory IDPs. With grain sizes, mineralogy, mineral chemistry, and an oxygen isotopic composition like those of refractory inclusions, we conclude that Inti is a refractory inclusion that formed in the inner solar nebula. Identification of a particle that formed in the inner Solar System among the comet samples demonstrates that there was transport of materials from the inner to the outer nebula, probably either in a bipolar outflow or by turbulence.
- Research Organization:
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 949817
- Report Number(s):
- LLNL-JRNL-404406; TRN: US200909%%505
- Journal Information:
- Meteoritics and Planetary Science, vol. 43, N/A, November 1, 2008, pp. 1861-1877, Vol. 43
- Country of Publication:
- United States
- Language:
- English
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