Mineral chemistry of MUSES‐C Regio inferred from analysis of dust particles collected from the first‐ and second‐touchdown sites on asteroid Itokawa |
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| Authors: | Tomoki Nakamura Aiko Nakato Hatsumi Ishida Shigeru Wakita Takaaki Noguchi Michael E Zolensky Masahiko Tanaka Makoto Kimura Akira Tshuchiyama Toshihiro Ogami Takahito Hashimoto Mitsuru Konno Masayuki Uesugi Toru Yada Kei Shirai Akio Fujimura Ryuji Okazaki Scott A Sandford Yukihiro Ishibashi Masanao Abe Tatsuaki Okada Munetaka Ueno Junichiro Kawaguchi |
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| Institution: | 1. Division of Earth and Planetary Materials Science, Laboratory for Early Solar System Evolution, Graduate School of Science, Tohoku University, , Aoba, Sendai, Miyagi, 980‐8578 Japan;2. College of Science, Ibaraki University, , Mito, Ibaraki, 310‐8512 Japan;3. ARES, NASA Johnson Space Center, , Houston, Texas, 77058 USA;4. WEBRAM, SPring‐8, National Institute for Materials Science, , Sayo, Hyogo, 679‐5198 Japan;5. Department of Earth and Space Science, Graduate School of Science, Osaka University, , Toyonaka, 560‐0043 Japan;6. Hitachi High‐Technologies Corporation, , Hitachinaka, Ibaraki, 312‐8504 Japan;7. JAXA‐ISAS, , Sagamihara, Kanagawa, 229‐8510 Japan;8. Department of Earth and Planetary Science, Faculty of Science, Kyushu University, , Hakozaki, Fukuoka, 812‐8581 Japan;9. NASA Ames Research Center, , Moffett Field, California, USA |
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| Abstract: | The mineralogy and mineral chemistry of Itokawa dust particles captured during the first and second touchdowns on the MUSES‐C Regio were characterized by synchrotron‐radiation X‐ray diffraction and field‐emission electron microprobe analysis. Olivine and low‐ and high‐Ca pyroxene, plagioclase, and merrillite compositions of the first‐touchdown particles are similar to those of the second‐touchdown particles. The two touchdown sites are separated by approximately 100 meters and therefore the similarity suggests that MUSES‐C Regio is covered with dust particles of uniform mineral chemistry of LL chondrites. Quantitative compositional properties of 48 dust particles, including both first‐ and second‐touchdown samples, indicate that dust particles of MUSES‐C Regio have experienced prolonged thermal metamorphism, but they are not fully equilibrated in terms of chemical composition. This suggests that MUSES‐C particles were heated in a single asteroid at different temperatures. During slow cooling from a peak temperature of approximately 800 °C, chemical compositions of plagioclase and K‐feldspar seem to have been modified: Ab and Or contents changed during cooling, but An did not. This compositional modification is reproduced by a numerical simulation that modeled the cooling process of a 50 km sized Itokawa parent asteroid. After cooling, some particles have been heavily impacted and heated, which resulted in heterogeneous distributions of Na and K within plagioclase crystals. Impact‐induced chemical modification of plagioclase was verified by a comparison to a shock vein in the Kilabo LL6 ordinary chondrite where Na‐K distributions of plagioclase have been disturbed. |
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