TY - JOUR
T1 - Nanomorphology of Itokawa regolith particles
T2 - Application to space-weathering processes affecting the Itokawa asteroid
AU - Matsumoto, Toru
AU - Tsuchiyama, Akira
AU - Uesugi, Kentaro
AU - Nakano, Tsukasa
AU - Uesugi, Masayuki
AU - Matsuno, Junya
AU - Nagano, Takashi
AU - Shimada, Akira
AU - Takeuchi, Akihisa
AU - Suzuki, Yoshio
AU - Nakamura, Tomoki
AU - Nakamura, Michihiko
AU - Gucsik, Arnold
AU - Nagaki, Keita
AU - Sakaiya, Tatsuhiro
AU - Kondo, Tadashi
N1 - Funding Information:
We would like to thank all members of the sample curation teams at JAXA for giving us the opportunity to analyze the Itokawa particles. T.M. was supported by a Grant-in-Aid from the Japan Society for the Promotion of Science Fellows (JSPS; No. 13J01787). A.T. is supported by a Research Fellowship of the JSPS (Nos 24244086 and 15H05695). We would like to thank Dr. Tatsuhiro Michikami of Kinki University, Japan, for valuable discussions. The laser-induced shock experiment was performed under the joint research project of the Institute of Laser Engineering, Osaka University, Japan, and T. S. was supported by a Grant-in-Aid for Young Scientists B (No. 22740295) from the JSPS.
Publisher Copyright:
© 2016 Elsevier Ltd.
PY - 2016/8/15
Y1 - 2016/8/15
N2 - The morphological properties of 26 regolith particles from asteroid Itokawa were observed using scanning electron microscopes in combination with an investigation of their three-dimensional shapes obtained through X-ray microtomography. Surface observations of a cross section of the LL5 chondrite, and of crystals of olivine and pyroxene, were also performed for comparison. Some Itokawa particles have surfaces corresponding to walls of microdruses in the LL chondrite, where concentric polygonal steps develop and euhedral or subhedral grains exist. These formed through vapor growth owing to thermal annealing, which might have been caused by thermal metamorphism or shock-induced heating in Itokawa's parent body. Most of the Itokawa particles have more or less fractured surfaces, indicating that they were formed by disaggregation, probably caused by impacts. Itokawa particles with angular and rounded edges observed in computed tomography images are associated with surfaces exhibiting clear and faint structures, respectively. These surfaces can be interpreted by invoking different degrees of abrasion after regolith formation. A possible mechanism for the abrasion process is grain migration caused by impact-driven seismic waves. Space-weathered rims with blisters are distributed heterogeneously across the Itokawa regolith particles. This heterogeneous distribution can be explained by particle motion and fracturing, combined with solar-wind irradiation of the particle surfaces. The regolith activity-including grain motion, fracturing, and abrasion-might effectively act as refreshing process of Itokawa particles against space-weathered rim formation. The space-weathering processes affecting Itokawa would have developed simultaneously with space-weathered rim formation and regolith particle refreshment.
AB - The morphological properties of 26 regolith particles from asteroid Itokawa were observed using scanning electron microscopes in combination with an investigation of their three-dimensional shapes obtained through X-ray microtomography. Surface observations of a cross section of the LL5 chondrite, and of crystals of olivine and pyroxene, were also performed for comparison. Some Itokawa particles have surfaces corresponding to walls of microdruses in the LL chondrite, where concentric polygonal steps develop and euhedral or subhedral grains exist. These formed through vapor growth owing to thermal annealing, which might have been caused by thermal metamorphism or shock-induced heating in Itokawa's parent body. Most of the Itokawa particles have more or less fractured surfaces, indicating that they were formed by disaggregation, probably caused by impacts. Itokawa particles with angular and rounded edges observed in computed tomography images are associated with surfaces exhibiting clear and faint structures, respectively. These surfaces can be interpreted by invoking different degrees of abrasion after regolith formation. A possible mechanism for the abrasion process is grain migration caused by impact-driven seismic waves. Space-weathered rims with blisters are distributed heterogeneously across the Itokawa regolith particles. This heterogeneous distribution can be explained by particle motion and fracturing, combined with solar-wind irradiation of the particle surfaces. The regolith activity-including grain motion, fracturing, and abrasion-might effectively act as refreshing process of Itokawa particles against space-weathered rim formation. The space-weathering processes affecting Itokawa would have developed simultaneously with space-weathered rim formation and regolith particle refreshment.
KW - Asteroid Itokawa
KW - Regolith
KW - Space weathering
KW - Surface morphology
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U2 - 10.1016/j.gca.2016.05.011
DO - 10.1016/j.gca.2016.05.011
M3 - Article
AN - SCOPUS:84973102573
VL - 187
SP - 195
EP - 217
JO - Geochmica et Cosmochimica Acta
JF - Geochmica et Cosmochimica Acta
SN - 0016-7037
ER -