Oxygen isotopic composition of an enstatite ribbon of probable cometary origin

1Ryan C. Ogliore,2Donald E. Brownlee,3Kazuhide Nagashima,2David J. Joswiak,1Josiah B. Lewis,3Alexander N. Krot,1Kainen L. Utt,3Gary R. Huss
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13364]
1Department of Physics, Washington University in St. Louis, St. Louis, Missouri, 63130 USA
2Department of Astronomy, University of Washington, Seattle, Washington, 98195 USA
3Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Mānoa, Honolulu, Hawaii, 96822 USA
Published by arrangement with John Wiley & Sons

Filamentary enstatite crystals are found in interplanetary dust particles (IDPs) of likely cometary origin but are very rare or absent in meteorites. Crystallographic characteristics of filamentary enstatites indicate that they condensed directly from vapor. We measured the O isotopic composition of an enstatite ribbon from a giant cluster IDP to be δ18O = 25 ± 55, δ17O = 19 ± 129, ∆17O = 32 ± 134 (2σ errors), which is inconsistent at the 2σ level with the composition of the Sun inferred from the Genesis solar wind measurements. The particle’s O isotopic composition, consistent with the terrestrial composition, implies that it condensed from a gas of nonsolar O isotopic composition, possibly as a result of vaporization of disk region enriched in 16O‐depleted solids. The relative scarcity of filamentary enstatite in asteroids compared to comets implies either that this crystal condensed from dust vaporized in situ in the outer solar system where comets formed or it condensed in the inner solar system and was subsequently transported outward to the comet‐forming region.

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