TY - JOUR
T1 - Space weathered rims found on the surfaces of the Itokawa dust particles
AU - Noguchi, Takaaki
AU - Kimura, Makoto
AU - Hashimoto, Takahito
AU - Konno, Mitsuru
AU - Nakamura, Tomoki
AU - Zolensky, Michael E.
AU - Okazaki, Ryuji
AU - Tanaka, Masahiko
AU - Tsuchiyama, Akira
AU - Nakato, Aiko
AU - Ogami, Toshinori
AU - Ishida, Hatsumi
AU - Sagae, Ryosuke
AU - Tsujimoto, Shinichi
AU - Matsumoto, Toru
AU - Matsuno, Junya
AU - Fujimura, Akio
AU - Abe, Masanao
AU - Yada, Toru
AU - Mukai, Toshifumi
AU - Ueno, Munetaka
AU - Okada, Tatsuaki
AU - Shirai, Kei
AU - Ishibashi, Yukihiro
PY - 2014/2
Y1 - 2014/2
N2 - On the basis of observations using Cs-corrected STEM, we identified three types of surface modification probably formed by space weathering on the surfaces of Itokawa particles. They are (1) redeposition rims (2-3 nm), (2) composite rims (30-60 nm), and (3) composite vesicular rims (60-80 nm). These rims are characterized by a combination of three zones. Zone I occupies the outermost part of the surface modification, which contains elements that are not included in the unchanged substrate minerals, suggesting that this zone is composed of sputter deposits and/or impact vapor deposits originating from the surrounding minerals. Redeposition rims are composed only of Zone I and directly attaches to the unchanged minerals (Zone III). Zone I of composite and composite vesicular rims often contains nanophase (Fe,Mg)S. The composite rims and the composite vesicular rims have a two-layered structure: a combination of Zone I and Zone II, below which Zone III exists. Zone II is the partially amorphized zone. Zone II of ferromagnesian silicates contains abundant nanophase Fe. Radiation-induced segregation and in situ reduction are the most plausible mechanisms to form nanophase Fe in Zone II. Their lattice fringes indicate that they contain metallic iron, which probably causes the reddening of the reflectance spectra of Itokawa. Zone II of the composite vesicular rims contains vesicles. The vesicles in Zone II were probably formed by segregation of solar wind He implanted in this zone. The textures strongly suggest that solar wind irradiation damage and implantation are the major causes of surface modification and space weathering on Itokawa.
AB - On the basis of observations using Cs-corrected STEM, we identified three types of surface modification probably formed by space weathering on the surfaces of Itokawa particles. They are (1) redeposition rims (2-3 nm), (2) composite rims (30-60 nm), and (3) composite vesicular rims (60-80 nm). These rims are characterized by a combination of three zones. Zone I occupies the outermost part of the surface modification, which contains elements that are not included in the unchanged substrate minerals, suggesting that this zone is composed of sputter deposits and/or impact vapor deposits originating from the surrounding minerals. Redeposition rims are composed only of Zone I and directly attaches to the unchanged minerals (Zone III). Zone I of composite and composite vesicular rims often contains nanophase (Fe,Mg)S. The composite rims and the composite vesicular rims have a two-layered structure: a combination of Zone I and Zone II, below which Zone III exists. Zone II is the partially amorphized zone. Zone II of ferromagnesian silicates contains abundant nanophase Fe. Radiation-induced segregation and in situ reduction are the most plausible mechanisms to form nanophase Fe in Zone II. Their lattice fringes indicate that they contain metallic iron, which probably causes the reddening of the reflectance spectra of Itokawa. Zone II of the composite vesicular rims contains vesicles. The vesicles in Zone II were probably formed by segregation of solar wind He implanted in this zone. The textures strongly suggest that solar wind irradiation damage and implantation are the major causes of surface modification and space weathering on Itokawa.
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U2 - 10.1111/maps.12111
DO - 10.1111/maps.12111
M3 - Article
AN - SCOPUS:84893086317
VL - 49
SP - 188
EP - 214
JO - Meteoritics and Planetary Science
JF - Meteoritics and Planetary Science
SN - 1086-9379
IS - 2
ER -