Mass-independent Oxygen Isotope Variation in the Solar Nebula

Abstract

Research Article| January 01, 2008 Mass-independent Oxygen Isotope Variation in the Solar Nebula Edward D. Young; Edward D. Young Department of Earth and Space Sciences, Institute of Geophysics and Planetary Physics, University of California Los Angeles, Los Angeles, California 90095, U.S.A., eyoung@ess.ucla.edu Search for other works by this author on: GSW Google Scholar Kyoshi Kuramoto; Kyoshi Kuramoto Department of Cosmosciences Sciences, Hokkaido University, Sapporo, 060-0810, Japan Search for other works by this author on: GSW Google Scholar Rudolph A. Marcus; Rudolph A. Marcus Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, U.S.A. Search for other works by this author on: GSW Google Scholar Hisayoshi Yurimoto; Hisayoshi Yurimoto Department of Natural History Sciences, Hokkaido University, Sapporo 060-0810, Japan Search for other works by this author on: GSW Google Scholar Stein B. Jacobsen Stein B. Jacobsen Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, U.S.A. Search for other works by this author on: GSW Google Scholar Author and Article Information Edward D. Young Department of Earth and Space Sciences, Institute of Geophysics and Planetary Physics, University of California Los Angeles, Los Angeles, California 90095, U.S.A., eyoung@ess.ucla.edu Kyoshi Kuramoto Department of Cosmosciences Sciences, Hokkaido University, Sapporo, 060-0810, Japan Rudolph A. Marcus Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, U.S.A. Hisayoshi Yurimoto Department of Natural History Sciences, Hokkaido University, Sapporo 060-0810, Japan Stein B. Jacobsen Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, U.S.A. Publisher: Mineralogical Society of America First Online: 03 Mar 2017 © The Mineralogical Society Of America Reviews in Mineralogy and Geochemistry (2008) 68 (1): 187–218. https://doi.org/10.2138/rmg.2008.68.9 Article history First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Edward D. Young, Kyoshi Kuramoto, Rudolph A. Marcus, Hisayoshi Yurimoto, Stein B. Jacobsen; Mass-independent Oxygen Isotope Variation in the Solar Nebula. Reviews in Mineralogy and Geochemistry 2008;; 68 (1): 187–218. doi: https://doi.org/10.2138/rmg.2008.68.9 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyReviews in Mineralogy and Geochemistry Search Advanced Search Abstract In this chapter we compare and contrast chemical and photochemical pathways for mass-independent fractionation (MIF) of oxygen isotopes in the solar nebula. We begin by assessing the galactic evolution model for oxygen isotope variation in the Solar System in order to compare the predictions of a leading nucleosynthetic model with those of the chemical models. There are two fundamentally different classes of possible chemical mechanisms for mass-independent oxygen isotope fractionation in the early Solar System. One is symmetry-induced intramolecular vibrational disequilibrium of vibrationally excited reactant oxygen-bearing molecules. The other is isotope selective photodissociation of CO coupled with self-shielding and formation of H2O. Symmetry-induced fractionation is an experimentally verified process with solid theoretical foundations. It is observed to occur in Earth’s atmosphere. It could have resulted in preservation of oxygen MIF effects only if mediated by dust grain surfaces. CO self-shielding is an attractive hypothesis for the origin of mass-independent oxygen isotope fractionation in the early Solar System because it appeals to a process that apparently occurs in the interstellar medium, but it lacks experimental verification. Three astrophysical settings for CO self-shielding are proposed as sites for generating Δ17O variability in the early Solar System. One is the inner annulus of the protostellar disk at relatively high temperature. Another is the surface of the disk high above the midplane where light from the central star grazes the gas and dust of the disk, resulting in a zone of active CO predissociation and self-shielding. Interstellar light illuminating the disk at high incident angles causes a similar horizon of CO photodestruction. Variations in 16O could also have been inherited from self-shielding by CO in the molecular cloud that gave rise to the protosun. The overall consequence of CO self-shielding is conversion of CO gas to 16O-poor H2O. A key difference between galactic evolution, chemically-induced MIF effects, and CO self-shielding is the predicted relative oxygen isotopic compositions of primeval dust and the Sun. Therefore, the oxygen isotopic composition of the Sun will be a crucial arbiter that may permit us to narrow the list of possible origins for oxygen MIF in the early Solar System. 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