Diffusion of Oxygen Isotopes in Thermally Evolving Planetesimals and Size Ranges of Presolar Silicate Grains

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書誌事項

公開日
2017-02-10
資源種別
journal article
権利情報
  • https://iopscience.iop.org/page/copyright
  • https://iopscience.iop.org/info/page/text-and-data-mining
DOI
  • 10.3847/1538-4357/aa5b8c
公開者
American Astronomical Society

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説明

<jats:title>Abstract</jats:title> <jats:p>Presolar grains are small particles found in meteorites through their isotopic compositions, which are considerably different from those of materials in the solar system. If some isotopes in presolar grains diffused out beyond their grain sizes when they were embedded in parent bodies of meteorites, their isotopic compositions could be washed out, and hence the grains could no longer be identified as presolar grains. We explore this possibility for the first time by self-consistently simulating the thermal evolution of planetesimals and the diffusion length of <jats:sup>18</jats:sup>O in presolar silicate grains. Our results show that presolar silicate grains smaller than ∼0.03 <jats:italic>μ</jats:italic>m cannot keep their original isotopic compositions even if the host planetesimals experienced a maximum temperature as low as 600 °C. Since this temperature corresponds to that experienced by petrologic type 3 chondrites, isotopic diffusion can constrain the size of presolar silicate grains discovered in such chondrites to be larger than ∼0.03 <jats:italic>μ</jats:italic>m. We also find that the diffusion length of <jats:sup>18</jats:sup>O reaches ∼0.3–2 <jats:italic>μ</jats:italic>m in planetesimals that were heated up to 700–800°C. This indicates that, if the original size of presolar grains spans a range from ∼0.001 <jats:italic>μ</jats:italic>m to ∼0.3 <jats:italic>μ</jats:italic>m like that in the interstellar medium, then the isotopic records of the presolar grains may be almost completely lost in such highly thermalized parent bodies. We propose that isotopic diffusion could be a key process to control the size distribution and abundance of presolar grains in some types of chondrites.</jats:p>

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