Consortium study of the largest Itokawa particle.
M. Uesugi1, A. Tsuchiyama2, K. Uesugi3, A. Takeuchi3, Y.
Suzuki3, J. Park4, K. Nagao5, K. Nishiizumi6, D. Nakashima7, N.
T. Kita8, F. Langenhorst9, L. P. Keller10, T. Yada1, Y. Karouji1, A.
Nakato1, K. Kumagai1, T. Okada1,2, M. Abe1,2, 1Institute of Spaceand Astronautical Science, Japan Aerospace Exploration Agency(JAXA), 2Kyoto University, 3Japan synchrotron radiation
Research institute (JASRI), 4Rutgers U., 5Tokyo University,6
University of California, 7Tohoku University, 8University ofWisconsin-Madison, 9Friedrich Schiller University Jena,
10NASA/JSC.
E-mail: uesugi@planeta.sci.isas.jaxa.jp.
Introduction: RA-QD02-0136-01 is currently the largest
sample of Hayabusa-returned samples recovered from asteroid
Itokawa [1-6]. Major axis of the particle ra is around 310 µm. We
constructed a consortium for a series of studies of this particle,
and started non-destructive analysis.
We report the result of synchrotron radiation computed tomography (SR-CT) and research plan of subsequent studies.
Result of SR-CT observation: Imaging CT with analyticaldual energy tomography [7], X-ray diffraction CT (XRD-CT, [8])and projection CT were applied to the sample, using special
holder for SR-CT which enable us to observe the sample without
any adhesives and direct exposure to the terrestrial atmosphere.
We confirmed that the particle is mainly composed of olivine,
low and high-Ca pyroxene, plagioclase and troilite using the analytical dual energy tomography. However, we could not obtain
three-dimensional data of the whole particle because of the low
X-ray energy used in the experiment, 7keV and 10keV. By applying the projection CT analysis with higher X-ray energy, 20keV,
and comparing it to the result of analytical dual energy tomography, we could obtain the distribution of mineral phases of thewhole particle. The distribution of the mineral phases was confirmed by XRD-CT method.
We also found anomalous number of voids in the CT images.
Two-dimensionally, the voids are trails of elongated pores [1],and three-dimensionally, the voids are connected each other, andform irregular shaped surface. Porosity of the particle is 16% andlarger than the range of Hayabusa returned samples analyzed in
the preliminary examinations (2-14%, [5]). Some of the voids
seem to be healed incompletely, suggesting moderate thermal
annealing after the breaking of the particle, probably on theparent body of Itokawa.
Future research plan: Currently, we finished the CT observation and high resolution observation of the surface of the particle by FE-SEM. We will cut the sample into several pieces after
the SEM observation, and will perform further destructive analyses such as TEM observation of space weathering rim, solarflare track and dislocations of the crystal, oxygen isotopic analysis, Ar-Ar age analysis and analysis of cosmogenic nuclides.
References: [1] Nakamura et al. 2011. Science 333:11131116. [2] Yurimoto et al. 2011. Science 333:1116-1119. [3]Ebihara et al. 2011. Science 333:1119-1121. [4] Noguchi et al.
(2011) Science 333:1121-1125. [5] Tsuchiyama et al. 2011. Science 333:1125-1128. [6] Nagao et al. 2011. Science 333:11281131. [7] Tsuchiyama et al. 2013 Geochimica Cosmochica Acta
116:5-16 [8]Uesugi et al. 2013. Geochimica Cosmochica Acta
116: 17-32.