[P-PS03] 太陽系小天体：太陽系の形成と進化における最新成果と今後の展望

[PPS03-06] リュウグウ帰還試料キュレーションの現状とOSIRIS-REx帰還試料キュレーション準備について

*矢田 達¹、安部 正真¹、西村 征洋¹、岡田 達明¹、深井 稜汰¹、坂本 佳奈子¹、与賀田 佳澄¹、畠田 健太朗^1,2、宮﨑 明子¹、長島 加奈¹、田原 瑠依¹、金丸 礼¹、中野 有紗¹、小嶋 智子¹、人見 勇矢^1,2、杉山 由香¹、熊谷 和也^1,2、副島 広道^1,2、石崎 拓也¹、古川 聡一朗³、菅原 春菜¹、鈴木 志野¹、杉田 精司³、長 勇一郎³、湯本 航生³、矢部 佑奈³、森 晶輝³、古市 圭佑³、愛敬 雄太³、Bibring Jean-Pierre⁴、Pilorget Cedric⁴、Brunetto Rosario⁴、Riu Lucie⁴、Loizeau Damien⁴、Lourit Lionel⁴、Le Pivert-Jolivet Tania⁴、Lantz Cateline⁴、Hamm Vincent⁴、Lequertier Guillaume⁴、Carter John⁴、臼井 寛裕¹、藤本 正樹¹ (1.宇宙航空研究開発機構、2.マリンワーク・ジャパン、3.東京大学、4.パリ･サクレー大学宇宙物理学研究所)

キーワード：サンプルリターン、キュレーション、はやぶさ2、リュウグウ、C型小惑星、OSIRIS-REx

Since C-type near-Earth asteroid (NEA) Ryugu samples returned by Hayabusa2 in Dec 2020, initial descriptions of bulk samples have been conducted, including optical observations, weight measurements, an FT-IR analyses, an infrared imager MicrOmega analyses, and a visible spectral measurement. These analyses revealed that the Ryugu samples are composed mainly of hydrous minerals and contain carbonates and organics and are most similar to CI chondrites [1,2]. Nearly 800 individual grains have been picked up so far for initial descriptions including the optical microscope observation and the weight measurements. Subsequently, the FT-IR, the MicrOmega, and the visible spectra analyses for the newly-described grains were followed. Parallel to the initial descriptions at our curation facility, Ryugu samples were distributed to initial analysis and phase2 curation teams in June 2021. These teams revealed that Ryugu samples were most similar to CI chondrites in chemistry and mineralogy with the exceptions of several features. These include that the Ryugu samples contain less water and heterogeneously distributed insoluble organic matters combined with phyllosilicates, and have petrological features such as presences of chips of chondrules and Ca- and Al-rich inclusions [3-7]. Ryugu samples have been distributed to selected principal investigators (PIs) of the Announcement of Opportunity (AO). In the AO1 announced in Jan 2021, 40 proposals were selected for samples distributions in June 2020 and the samples have been distributed at the end of 2022. In the AO2 announced in June 2022, 38 proposals were selected in Jan 2023 and we started distributing samples to the selected PIs in this Feb. AO3 has been announced recently, and its result will be announced this summer.
The OSIRIS-REx, the asteroid explorer by NASA, will return samples to the Earth from the B-type NEA Bennu on Sep. 23, 2023. Based on the memorandum of understanding (MOU) between JAXA and NASA, JAXA shared 10 wt% of Ryugu samples with NASA in Dec 2021, and in return NASA will provide 0.5 wt% of returned Bennu samples with JAXA. As the Bennu samples recovered in the sample canister of the OSIRIS-REx are estimated to be 250±101 g [8], JAXA will receive 0.5 wt% of returned Bennu samples (estimated to be 1.25±0.5 g) within a year after their return to the Earth. Construction of a new clean room was completed last Sep, and new clean chambers for handling and preserving allocated Bennu samples will be installed in the clean room this year. Instruments for initial descriptions are under development, and will be ready to use this year. After receiving the allocated Bennu samples, we plan to perform the preliminary examinations of the samples and upload the preliminary data in a database system, similar to the Ryugu samples. We also plan to announce the AO for the Bennu samples, and call for proposals that mainly focused on comparative studies between the Bennu and Ryugu samples.
References: [1] Yada T. et al. (2022) Nat. Astron. 6, 214. [2] Pilorget C. et al. (2022) Nat. Astron. 6, 221. [3] Nakamura E. et al. (2022) Proc. Japan Acad. B 98, 227. [4] Yokoyama T. et al. (2022) Science, DOI: 10.1126/science.abn7850. [5] Ito M. et al. (2022) Nat. Astron. 6, 1163. [6] Nakamura T. et al. (2022) Science, DOI: 10.1126/science.abn8671. [7] Noguchi T. et al. (2022) Nat. Astron. https://doi.org/10.1038/s41550-022-01841-6. [8] Lauretta D. S. et al. (2022) Science 377, 285.