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Type I Cosmic Spherules: Key to a Major, But Poorly Sampled, Asteroid Population?Herzog et al. have determined Fe, 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. Isotopic fractionation for all three elements is typically large, approx. 16%/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 compared to ratios in bulk chondrites and chondritic metal. Although the calculated pre-atmospheric Fe/Ni ratio for the spherules is relatively constant at 19 +/- 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 or = 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
20000093316
Acquisition Source
Johnson Space Center
Document Type
Preprint (Draft being sent to journal)
Authors
Nyquist, L. E. (NASA Johnson Space Center Houston, TX United States)
Date Acquired
September 7, 2013
Publication Date
January 1, 1999
Subject Category
Astrophysics
Meeting Information
Meeting: Extra-Terrestrials Materials
Location: KWA-Maritane
Country: South Africa
Start Date: July 6, 1999
End Date: July 8, 1999
Sponsors: Lunar and Planetary Inst., Meteoritical Society
Funding Number(s)
PROJECT: RTOP 344-31-30-21
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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