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Efficient mixing of the solar nebula from uniform Mo isotopic composition of meteorites


The abundances of elements and their isotopes in our Galaxy show wide variations, reflecting different nucleosynthetic processes in stars and the effects of Galactic evolution1. These variations contrast with the uniformity of stable isotope abundances for many elements in the Solar System2,3, which implies that processes efficiently homogenized dust and gas from different stellar sources within the young solar nebula. However, isotopic heterogeneity has been recognized on the subcentimetre scale in primitive meteorites4,5, indicating that these preserve a compositional memory of their stellar sources. Small differences in the abundance of stable molybdenum isotopes in bulk rocks of some primitive6,7,8 and differentiated7,9 meteorites, relative to terrestrial Mo, suggest large-scale Mo isotopic heterogeneity between some inner Solar System bodies, which implies physical conditions that did not permit efficient mixing of gas and dust. Here we report Mo isotopic data for bulk samples of primitive and differentiated meteorites that show no resolvable deviations from terrestrial Mo. This suggests efficient mixing of gas and dust in the solar nebula at least to 3 au from the Sun, possibly induced by magnetohydrodynamic instabilities10. These mixing processes must have occurred before isotopic fractionation of gas-phase elements and volatility-controlled chemical fractionations were established.

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Figure 1: Isotopic composition of Mo in meteorites.
Figure 2: Isotopic composition of Mo in bulk Allende and CAI 3659-B.

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We thank R. Clarke and G. MacPherson for providing the meteorite samples, N. Dauphas, H. Palme, D. Papanastassiou, A. Pietruszka and Q. Yin for discussions, and P. Tomascak for comments on the manuscript and technical support in the laboratory. Comments by S. Jacobsen have improved the presentation of various issues in this manuscript.

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Correspondence to Harry Becker.

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Becker, H., Walker, R. Efficient mixing of the solar nebula from uniform Mo isotopic composition of meteorites. Nature 425, 152–155 (2003).

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