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Extreme oxygen isotope ratios in the early Solar System


The origins of the building blocks of the Solar System can be studied using the isotopic composition of early planetary and meteoritic material. Oxygen isotopes in planetary materials show variations at the per cent level that are not related to the mass of the isotopes1,2; rather, they result from the mixture of components having different nucleosynthetic or chemical origins1,2,3. Isotopic variations reaching orders of magnitude in minute meteoritic grains are usually attributed to stellar nucleosynthesis before the birth of the Solar System, whereby different grains were contributed by different stars4,5. Here we report the discovery of abundant silica-rich grains embedded in meteoritic organic matter, having the most extreme 18O/16O and 17O/16O ratios observed (both 10-1) together with a solar silicon isotopic composition. Both O and Si isotopes indicate a single nucleosynthetic process. These compositions can be accounted for by one of two processes: a single exotic evolved star seeding the young Solar System6, or irradiation of the circumsolar gas by high energy particles accelerated during an active phase of the young Sun. We favour the latter interpretation, because the observed compositions are usually not expected from nucleosynthetic processes in evolved stars, whereas they are predicted by the selective trapping of irradiation products.

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Figure 1: Ion images of 16 O, 17 O, 18 O and 28 Si in organic pellets.
Figure 2: Oxygen isotopic composition of anomalous silica-rich grains compared with presolar grains, evolved stars and irradiation models.
Figure 3: Mineralogical observations of anomalous grains.


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A. Toppani, J. Kiener, A. Coc, N. Prantzos, M. Gounelle, V. Tatischeff, M. Chaussidon and B. Charoy are thanked for discussions, A. Kohler, B. Assouar, C. Clément and L. Marchal helped with SEM and FESEM, and T. Lhomme helped with the Raman laser. This work was supported by the Région Lorraine, and by PNP-INSU and PCMI-INSU grants.

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Correspondence to Jérôme Aléon.

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Supplementary information

Supplementary Discussion

This file includes a detailed discussion of sample preparation and ion probe analysis, along with a description of the irradiation model used in the calculations. (DOC 37 kb)

Supplementary Data

This Supplementary Table contains all oxygen and silicon data for the samples and reference materials. (DOC 84 kb)

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Aléon, J., Robert, F., Duprat, J. et al. Extreme oxygen isotope ratios in the early Solar System. Nature 437, 385–388 (2005).

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