[U-06_28PO1] New Progress toward the Understanding of Small Solar System Bodies

[U06-P16] Consortium Study of Troilite and Phosphate-bearing HAYABUSA Returned Samples

*Yuzuru KAROUJI¹, Masayuki UESUGI¹, Toru YADA¹, Yukihiro ISHIBASHI¹, Wataru SATAKE², Tatsuaki OKADA¹, Masanao ABE¹ (1.Japan Aerospace Exploration Agency, 2.Department of Earth and Planetary Science, University of Tokyo)

Keywords:HAYABUSA, Itokawa, troilite, phosphate, siderophile element, U-Pb dating

HAYABUSA returned samples have been shown as Itokawa origin by the preliminary examinations (e.g. Nakamura et al., 2011). Furthermore, international AO study has begun last year, and a formation process of asteroid Itokawa is becoming revealed.HAYABUSA returned samples are described initially by JAXA Extraterrestrial Sample Curation Team (ESCuTe), and a sample catalogue is prepared based on the data of initial description (e.g. Yada et al., 2014). More than 400 returned samples were described so far. These described samples are classified into four categories. A number of samples of each category to be distributed for international AO are decided based on the sample catalogue. But it is difficult to distribute such samples with rare characteristics in composition, mineralogy, structure, or size, although those samples should maintain scientifically important information.Therefore, in JAXA, ESCuTe started to organize the consortium studies in order to obtain the scientific information as many as possible from these samples (e.g. Yada et al., 2014; Uesugi et al., 2014). In this paper, we report the research plan for the particles mainly composed of FeS and which contain phosphate minerals.RA-QD02-0245 composed mainly of FeS (40 micron) with smaller attached olivine and pyroxene grains. This particle was analyzed by X-ray CT at SPring-8 for 3D texture without atmosphere. Two ultra-thin section will be made from the edge of this particle by FIB. The ultra-thin sections will be examined by TEM in detail for space-weathering effect on FeS surface. The main mass of this particle will be analyzed for chemical composition. Especially, the siderophile element composition gives us information on the formation process of Itokawa parent body.Some particles including phosphate mineral were found by the initial description. Because Ca-phosphate tends to be enriched in incompatible elements such as REEs, Th and U, we propose the investigation of U-Pb systematics using Nano-SIMS in order to study the history recorded in the phosphates. We will perform the U-Pb dating of the phosphates as many as possible and aim to understand the thermal history of Itokawa parent body such as crystallization age and the catastrophic collition if recorded.