EVALUATIONOFMODALABUNDANCESOFITOKAWA PARTICLES.
T. Yada1, M. Uesugi1, Y. Karouji1, Y. Ishibashi1, M. Abe1,2, T.
Okada1,2, S. Yakame3, A. Tsuchiyama4. 1Instit. Space Astronaut.
Sci. and 2Lunar Planet. Explor. Program Group, Japan Aerosp.
Explor. Agency, JAPAN. E-mail: yada@planeta.sci.isas.jaxa.jp.
3
Depart. Earth Planet. Sci., Grad. School Sci., Univ. Tokyo,
JAPAN. 4Depart. Earth Planet. Sci., Grad. School Sci., Kyoto
Univ., JAPAN.
Introduction: The Hayabusa spacecraft accompolishedtouchdowns onto a S-type asteroid Itokawa twice and returned its
reentry capsule to the Earth in June 2010 [1]. After it wasrecovered in the Australian desert and sent back to Japan, it wastreated in clean rooms of the extraterrestrial sample curation
center (ESCUC) of JAXA and finally returned samples wererecovered from the sample catcher, as described in [2]. Duringinitial descriptions of the recovered particles, they were analyzed
with SEM-EDS for their backscattered electron images andqualitative chemical compositions. With these data, we estimatedmodal abundances of Itokawa particles to understand theirgeneral characteristics [3].
Methods to estimate modal abundances: Twoapproximations have been applied to the estimation of the modal
abundances of Itokawa particles. One is that a particle is regarded
to be only composed of its major constituent mineral. The other isthat its volume is calculated by a cube of its major axis. The
modal abundance of Itokawa particles was estimated by summingup all of the estimated mineral volume of the initially describedparticles.
On the other hand, the modal abundance of Itokawa particles
were also determined from three-dimensional X-ray linear
attenuation coefficient (LAC) data for preliminary examined
Itokawa particles obtained by two energy synchrotron computed
tomography (CT) [4].
The latter is more accurate than the former, because theformer is based on two-dimensional surface data and ignored
minor minerals contained in the particles. However, the lattermethod could not have been applied to initial description for all
recovered particles, because contaminations by terrestrial air andglue and multiple preparation processes are inevitable for thelatter analyses.
Suggestion of different modal abundances in different
sampling point on the asteroid: The modal abundance obtainedby both the former and the latter indicated that they werecomparable to that of equilibrated LL chondrites [3, 4]. It wassuggested that that from a sample catcher room A was different
from that from room B. Because those from room A should havegathered the second touchdown point while room B should thefirst one, it was suggested that this could indicate local
heterogeneity of the surface of the asteroid Itokawa [3].
We are now planning to evaluate an error in the former
estimation, with comparing modal abundances obtained by bothmethods. We analyzed particles of Kilabo (LL6 chondrite) [5] byboth methods. Their data reductions are ongoing.
References: [1] Abe M. et al. (2011) LPS XLII: #1638. [2]Yada T. et al. (2013) MAPS, in press. [3] Yada T. et al. (2013)
LPS XLIV #1948. [4] Tsuchiyama A. et al. (2013) MAPS, in press.
[5] Russell S. et al. (2003) MAPS 38: A189.