Meteoritic Sulfur Isotope Anomalies

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Science  12 Aug 2005:
Vol. 309, Issue 5737, pp. 985
DOI: 10.1126/science.309.5737.985m

Most isotope fractionation during chemical reactions depends on the mass of the isotopes. However, mass independence has been seen for sulfur and oxygen isotope systems; distinct oxygen isotope variations are present in many primitive meteorites, and both sulfur and oxygen isotope variations occur in ultraviolet-driven reactions in Earth's upper atmosphere. Similar reactions have also been identified on Mars. Rai et al. (p. 1062) now show that similar sulfur isotope anomalies are present in sulfur minerals in a class of meteorites, the achnodrites, representing early planetesimals. This signature likely originated in the solar nebula and was somehow preserved during the accretion of these protoplanets. A similar process may explain the origin of the enigmatic oxygen isotope signature.

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