Space weathered rims found on the surfaces of the Itokawa dust particles

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...

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Bibliographic Details
Published in:	Meteoritics & planetary science Vol. 49; no. 2; pp. 188 - 214
Main Authors:	Noguchi, Takaaki, Kimura, Makoto, Hashimoto, Takahito, Konno, Mitsuru, Nakamura, Tomoki, Zolensky, Michael E., Okazaki, Ryuji, Tanaka, Masahiko, Tsuchiyama, Akira, Nakato, Aiko, Ogami, Toshinori, Ishida, Hatsumi, Sagae, Ryosuke, Tsujimoto, Shinichi, Matsumoto, Toru, Matsuno, Junya, Fujimura, Akio, Abe, Masanao, Yada, Toru, Mukai, Toshifumi, Ueno, Munetaka, Okada, Tatsuaki, Shirai, Kei, Ishibashi, Yukihiro
Format:	Journal Article
Language:	English
Published:	Hoboken Blackwell Publishing Ltd 01-02-2014 Wiley Subscription Services, Inc
Subjects:	Iron Minerals Nanostructure Particulate composites Rims Segregations Texture Weathering
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Summary:	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.
Bibliography:	ark:/67375/WNG-DMVFHRS5-3 istex:752F732BF65CCD11241D0B548C40EF7389CF1CB1 NASA JSPS KAKENHI - No. 2424408 ArticleID:MAPS12111 ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23
ISSN:	1086-9379 1945-5100
DOI:	10.1111/maps.12111