THREEDIMENSIONALSTRUCTURESOF
AGGREGATE-TYPE
ITOKAWAPARTICLESANALYZED BY TWO ENERGY SYNCHROTRONCOMPUTED TOMOGRAPHY.
T. Yada1, M. Uesugi1, K. Uesugi2, Y. Karouji1, Y. Suzuki2, A.
Takeuchi2, A. Tsuchiyama3, T. Kuzumaki4, T. Okada1, and M.
Abe1 1Inst. Space Astronaut. Sci., Japan Aerosp. Explor. Agency.
E-mail: yada@planeta.sci.isas.jaxa.jp. 2Japan Synchrotr. Radiat.
Res. Inst. 3Depart. Earth Planet. Sci., Grad. Sch. Sci., Kyoto Univ.
4
Depart. Mater. Sci., Grad. Sch. Engineer., Tokai Univ.
Introduction: Particle aggregation is one of the essential
processes in the early solar nebular [1, 2]. It should occur also on
the surfaces of asteroids, although their processes are poorly
understood. Hayabusa spacecraft returned samples from asteroid
Itokawa [3, 4]. Among Itokawa particles recovered from
Hayabusa’s sample catcher, there exist certain amount of
aggregate-type particles which are aggregate of small constituent
grains. In order to understand the aggregation processes onasteroid surface, we started studying about this type of Itokawa
particles.
Samples and Methods: We selected five Itokawa particles(RA-QD02-0184, RA-QD02-0236, RB-CV-0026, RB-CV-0036
and RB-CV-0044) which seems aggregate-type from theirsurface morphology in their electron micrographs for this study.
They were placed on SiN holders and analyzed by two energy
synchrotron computed tomography (CT) in BL47XU of SPring-8
for their three dimensional structures and mineral distributions[5].
Results: As a result of synchrotron CT, one of the particles is
not aggregate-type but enriched in cracks, which should havebeen misidentified as aggregate-type from its surface morphology.
Rest of them are aggregate-type, and they are divided into twogroups; the ones in which small constituent grains stick together
and the other which consist of small constituent grains boundeach other.
Discussion: The former type of aggregate Itokawa particles
could have been formed on the surface of low gravity conditions
like asteroid Itokawa. On the other hand, the latter type needs
higher temperature or higher gravitational forces in order to form
such a binding structure. This indicates that it would have been
formed in a lager parent asteroid before Itokawa.
Future works: We are now preparing simulated aggregate
particles made of soda-lime glass beads. With these particles, wewill test focused ion beam (FIB) process to make a ultra thinsection (UTS). After checks of whole the processes of transmitted
electron microscope (TEM) observation of their UTSs, we will
analyze the real Itokawa particles in order to observe detailstructures of grain boundaries of small constituent grains andclarify their formation processes. We are also planning toperform a test measurement of their fracture strength before
measurements of real Itokawa particles [6], in order to measure
one of the essential physical properties of asteroid regoliths.
References: [1] Dominik C. and Tielens A. G. G. M. 1997.
Astrophys. J. 480, 647. [2] Poppe T., Blum J. and Henning T.
2000. , Astrophys. J. 533, 454. [3] Abe M. et al. (2011) LPSXXXXII, #1638. [4] Nakamura T. et al. (2011) Science 333,1113. [5] Tsuchiyama A. et al. (2011) Science 333, 1125. [6]Kuzumaki T. et al. (2012) Diam. Relat. Mater. 25, 1.