Diffraction study of the grain (C2054,0,35,4) obtained by the NASA Stardust Mission

Graduate School of Life Science, University of Hyogo* Department of Earth and Planetary Science, University of Tokyo, Japan** NASA Johnson Space Center, U.S.A.*** High Energy Accelerator Research Org. (KEK), Japan****
○Kenji Hagiya* Takashi Mikouchi** Michael E Zolensky*** Kazumasa Ohsumi****

One of the Comet Wild-II particles (C2054,0,35,4) collected by the NASA Stardust Mission was analyzed by X-ray diffraction method. The sample with about 10 micrometers in size was attached to the end of a thin glass fiber. Diffraction experiment was carried out using the microbeam diffraction system placed at BL-4B1 of PF, KEK. The incident beam is limited to 1.6 micrometer in diameter by a micro-pinhole set just upstream of the sample. Laue photograph was successfully taken on an imaging plate by 30 minutes exposure using polychromatic X-ray of synchrotron radiation operated at energy of 2.5GeV.
All Laue spots are well indexed by three domains of one olivine and two orthopyroxenes. The axial ratio of each domain is refined based on the positions of Laue spots, shown in the table. It is shown that the olivine is conceived to be forsterite according to the Vegard’s low. The structure refinement including site occupancies of Mg and Fe of olivine was carried out based on the diffraction intensities of Laue spots. The obtained value of Fe/(Mg+Fe) is around 0.11. This value is compatible with the results obtained from the axial ratio. The structure of orthopyroxene was also refined, and the value of Fe/(Mg+Fe) is also around 0.11.