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Type I Cosmic Spherules: Key to a Major, But Poorly Sampled, Asteroid PopulationFe, Ni, and Cr abundances in Type I cosmic spherules recovered from the deep sea, and also the isotopic fractionation of these elements during passage of the spherules through the terrestrial atmosphere was determined. Isotopic fractionation for all three elements is typically large, approx. 16%o/amu, corresponding to evaporative mass losses of approx. 80-85%, assuming Rayleigh distillation from an open system. The corrected, pre-atmospheric, Cr/Ni and Fe/Ni ratios are shown, where they are compared to these ratios in bulk chondrites and chondritic metal. Although the calculated pre-atmospheric Fe/Ni ratio for the spherules is relatively constant at 19 plus or minus 4 (sigma (sub mean)), the calculated pre-atmospheric Cr/Ni ratios vary by about two orders of magnitude. The Cr/Ni ratios are thus powerful discriminators for possible modes of origin of the spherules. For example, iron meteorites typically have low Cr contents and low Cr/Ni ratios, less than or equal to 3 x 10(exp -4). Thus, Type I spherules do not appear to be ablation products of iron meteorites, in contrast to an earlier suggestion..
Document ID
20000034797
Document Type
Conference Paper
Authors
Nyquist, Larry E. (NASA Johnson Space Center Houston, TX United States)
Date Acquired
August 19, 2013
Publication Date
January 1, 1999
Publication Information
Publication: Workshop on Extraterrestrial Materials from Cold and Hot Deserts
Subject Category
Astrophysics
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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IDRelationTitle20000034770Analytic PrimaryWorkshop on Extraterrestrial Materials from Cold and Hot Deserts
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