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Science 19 August 2005:
Vol. 309. no. 5738, pp. 1233 - 1236
DOI: 10.1126/science.1115053
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Reports

Osmium Isotope Evidence for an s-Process Carrier in Primitive Chondrites

A. D. Brandon,1*{dagger} M. Humayun,2{dagger} I. S. Puchtel,3 I. Leya,4 M. Zolensky5

Osmium extracted from unequilibrated bulk chondrites has isotope anomalies consistent with an insoluble s-process carrier, termed Os(i) here. Osmium from metamorphosed bulk chondrites does not have isotope anomalies, implying that the Os(i) carrier was destroyed by metamorphism. The isotopic homogeneity of metamorphosed bulk chondrites is consistent with extremely effective mixing of presolar grains from varied sources in the nebula. Osmium in the Os(i) carrier is likely from nucleosynthetic sites with a neutron density about two to four times as high as that of the average solar s-process Os.

1 NASA Johnson Space Center, Mail Stop KR, Houston, TX 77058, USA.
2 National High Magnetic Field Laboratory and Department of Geological Sciences, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, FL 32310, USA.
3 Department of Geology, University of Maryland, College Park, MD 20742, USA.
4 Physikalisches Institut, Universität Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland.
5 NASA JSC, Mail Stop KT, Houston, TX 77058, USA.

{dagger} These authors contributed equally to this work.

* To whom correspondence should be addressed. E-mail: alan.d.brandon1{at}jsc.nasa.gov

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