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Science 19 October 2007:
Vol. 318. no. 5849, pp. 433 - 435
DOI: 10.1126/science.1145528
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Reports

Constraints on Neon and Argon Isotopic Fractionation in Solar Wind

Alex Meshik,1* Jennifer Mabry,1 Charles Hohenberg,1 Yves Marrocchi,1 Olga Pravdivtseva,1 Donald Burnett,2 Chad Olinger,3 Roger Wiens,4 Dan Reisenfeld,5 Judith Allton,6 Karen McNamara,6 Eileen Stansbery,7 Amy J. G. Jurewicz8

To evaluate the isotopic composition of the solar nebula from which the planets formed, the relation between isotopes measured in the solar wind and on the Sun's surface needs to be known. The Genesis Discovery mission returned independent samples of three types of solar wind produced by different solar processes that provide a check on possible isotopic variations, or fractionation, between the solar-wind and solar-surface material. At a high level of precision, we observed no significant inter-regime differences in 20Ne/22Ne or 36Ar/38Ar values. For 20Ne/22Ne, the difference between low- and high-speed wind components is 0.24 ± 0.37%; for 36Ar/38Ar, it is 0.11 ± 0.26%. Our measured 36Ar/38Ar ratio in the solar wind of 5.501 ± 0.005 is 3.42 ± 0.09% higher than that of the terrestrial atmosphere, which may reflect atmospheric losses early in Earth's history.

1 Physics Department, Washington University, St. Louis, MO 63130, USA.
2 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.
3 Neutron Science and Technology, MS H803, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
4 Space Science and Applications, MS D466, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
5 Physics and Astronomy Department, University of Montana, SC 121, 32 Campus Drive, MS 1080, Missoula, MT 59812, USA.
6 NASA/Johnson Space Center (JSC), Mail Code KT, Houston, TX 77058, USA.
7 NASA/JSC, Mail Code KA, Houston, TX 77058, USA.
8 Center for Meteorite Studies, Arizona State University, Mail Code 1404, Tempe, AZ 85287, USA.

* To whom correspondence should be addressed. E-mail: am{at}physics.wustl.edu

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