Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5779987 | Earth and Planetary Science Letters | 2017 | 10 Pages |
Abstract
In order to explore the link between comet 81P/Wild 2 and materials in primitive meteorites, seven particles 5 to 15 μm in diameter from comet 81P/Wild 2 have been analyzed for their oxygen isotope ratios using a secondary ion mass spectrometer. Most particles are single minerals consisting of olivine or pyroxene with Mg# higher than 85, which are relatively minor in 81P/Wild 2 particles (â¼1/3 of the 16O-poor cluster). Four particles extracted from Track 149 are 16O-poor and show Î17O (=δO17â0.52ÃδO18) values from â2â° to +1â°, similar to previous studies, while one enstatite (En99) particle shows lower Î17O value of â7±4â°(2Ï). This compositional range has not been reported among 16O-poor particles in 81P/Wild 2, but is commonly observed among chondrules in carbonaceous chondrites and in particular in CR chondrites. The distribution in Î17O indicates that 16O-poor 81P/Wild 2 particles are most similar to chondrules (and their fragments) in the CR chondrites and Tagish Lake-like WIS91600 chondrite chondrule silicate grains, which indicates that they likely come from a reservoir with similar dust/ice ratios as CR chondrites and WIS91600. However, differences in the Mg# distribution imply that the 81P/Wild 2 reservoir was comparatively more oxidized, with a higher dust enrichment. Two nearly pure enstatite grains from track 172 are significantly enriched in 16O, with δ18O values of â51.2±1.5â°(2Ï) and â43.0±1.3â°(2Ï), respectively, and Î17O values of â22.3±1.9â°(2Ï) and â21.3±2.3â°(2Ï), respectively. They are the first 16O-rich pyroxenes found among 81P/Wild 2 particles, with similar Î17O values to those of 16O-rich low-iron, manganese-enriched (LIME) olivine and CAI (calcium and aluminum-rich inclusions) - like particles from 81P/Wild 2. The major element and oxygen isotopic compositions of the pyroxenes are similar to those of enstatite in amoeboid olivine aggregates (AOAs) in primitive chondrites, in which 16O-rich pyroxenes have previously been found, and thus suggest a condensation origin.
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Physical Sciences and Engineering
Earth and Planetary Sciences
Earth and Planetary Sciences (General)
Authors
Céline Defouilloy, Daisuke Nakashima, David J. Joswiak, Donald E. Brownlee, Travis J. Tenner, Noriko T. Kita,