TY - JOUR
T1 - Mineral chemistry of MUSES-C Regio inferred from analysis of dust particles collected from the first- and second-touchdown sites on asteroid Itokawa
AU - Nakamura, Tomoki
AU - Nakato, Aiko
AU - Ishida, Hatsumi
AU - Wakita, Shigeru
AU - Noguchi, Takaaki
AU - Zolensky, Michael E.
AU - Tanaka, Masahiko
AU - Kimura, Makoto
AU - Tshuchiyama, Akira
AU - Ogami, Toshihiro
AU - Hashimoto, Takahito
AU - Konno, Mitsuru
AU - Uesugi, Masayuki
AU - Yada, Toru
AU - Shirai, Kei
AU - Fujimura, Akio
AU - Okazaki, Ryuji
AU - Sandford, Scott A.
AU - Ishibashi, Yukihiro
AU - Abe, Masanao
AU - Okada, Tatsuaki
AU - Ueno, Munetaka
AU - Kawaguchi, Junichiro
PY - 2014/2
Y1 - 2014/2
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=84893835772&partnerID=8YFLogxK
U2 - 10.1111/maps.12247
DO - 10.1111/maps.12247
M3 - Article
AN - SCOPUS:84893835772
SN - 1086-9379
VL - 49
SP - 215
EP - 227
JO - Meteoritics and Planetary Science
JF - Meteoritics and Planetary Science
IS - 2
ER -