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Boron abundances and isotopic ratios of olivine grains on Itokawa returned by the Hayabusa spacecraft

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Hoppe,  P.
Particle Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

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Ott,  U.
Biogeochemistry, Max Planck Institute for Chemistry, Max Planck Society;

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Citation

Fujiya, W., Hoppe, P., & Ott, U. (2016). Boron abundances and isotopic ratios of olivine grains on Itokawa returned by the Hayabusa spacecraft. Meteoritics and Planetary Science, 51(9), 1721-1729.


Cite as: https://hdl.handle.net/11858/00-001M-0000-002C-E709-F
Abstract
We report the B abundances and isotopic ratios of two olivine grains from the S-type asteroid Itokawa sampled by the Hayabusa spacecraft. Olivine grains from the Dar al Gani (DaG) 989 LL6 chondrite were used as a reference. Since we analyzed polished thin sections in both cases, we expect the contribution from the solar wind B (rich in B-10) to be minimal because the solar wind was implanted only within very thin layers of the grain surface. The Itokawa and DaG 989 olivine grains have homogeneous B abundances (similar to 400ppb) and B-11/B-10 ratios compatible with the terrestrial standard and bulk chondrites. The observed homogeneous B abundances and isotopic ratios of the Itokawa olivine grains are likely the result of thermal metamorphism which occurred in the parent asteroid of Itokawa, which had a similar composition as LL chondrites. The chondritic B isotopic ratios of the Itokawa samples suggest that they contain little cosmogenic B (from cosmic-ray spallation reactions) rich in B-10. This observation is consistent with the short cosmic-ray exposure ages of Itokawa samples inferred from the small concentrations of cosmogenic Ne-21. If other Itokawa samples have little cosmogenic B as well, the enrichment in B-10 found previously on the surface of another Itokawa particle (as opposed to the bulk grain study here) may be attributed to implanted solar wind B.