講演情報
[PPS12-02]Organic Functional Group Analysis of Asteroid Bennu Samples by Infrared and N-K-Edge Partial Fluorescence Yield X-Ray Absorption Spectroscopies
*癸生川 陽子1、薮田 ひかる2、小松 睦美3、橋口 未奈子4、松本 徹5、菅 大暉6、奈良岡 浩7、榎戸 祐馬8、坂本 佳奈子8、臼井 寛裕8、橘 省吾9 (1.東京科学大学、2.広島大学、3.埼玉県立大学、4.名古屋大学、5.京都大学、6.高輝度光科学研究センター、7.九州大学、8.宇宙科学研究所、9.東京大学)
キーワード：
小惑星、Bennu、有機物
The OSIRIS-REx mission returned samples from the carbonaceous asteroid Bennu, enabling comparison with Ryugu and aqueously altered carbonaceous chondrites. Although Bennu and Ryugu share many mineralogical similarities, differences in organic chemistry have been reported [1,2]. To characterize organic functional group chemistry, we conducted micro-FTIR and partial fluorescence yield N K-edge X-ray absorption near-edge structure (PFY-N-XANES) analyses on intact Bennu particles and their insoluble organic matter (IOM).
FTIR spectra of Bennu show typical hydrated chondrite features, including silicates, OH, carbonates, and aliphatic C–H, closely resembling Ryugu. Bennu samples exhibit slightly higher CH2/CH3 ratios than Ryugu [3,4] and CM/CI chondrites. Bennu IOM displays strong aliphatic C–H along with C=O and aromatic C=C features. Higher CH2/CH3 ratios in IOM compared to intact samples suggest preferential loss of short-chain, CH3-rich compounds during solvent extraction and acid treatment.
PFY-N-XANES reveals three nitrogen bonding states: (A) imine/pyridinic N (N=C), (B) nitrile/pyridinic N, and (C) pyrrolic N/amine/amide/ammonium species (N-C,H). Intact samples show substantial heterogeneity, whereas IOM is more homogeneous and enriched in N-heterocycles. Compared to CI and CM chondrites [5], Bennu exhibits greater diversity in nitrogen functional groups. Differences between intact samples and IOM indicate that single-bonded nitrogen (N-C,H) is partly associated with soluble or acid-labile fractions.
Overall, the diversity of organic functional groups in Bennu is consistent with its rubble-pile structure and heterogeneous aqueous alteration history [6].
References:
[1] Lauretta D. et al. (2024) Meteorit. Planet. Sci. 59, 2543–2486.
[2] Glavin D. et al. (2025) Nat. Astron. 9, 199–210.
[3] Yabuta H. et al. (2023) Science 379, eabn9057.
[4] Kebukawa Y. et al. (2024) Meteorit. & Planet. Sci. 59, 1845–1858.
[5] Kebukawa Y. et al. (2025) Goldschmidt 2025, Abstract doi:10.7185/gold2025.30315.
[6] Mojarro A. et al. (2025) PNAS 122, e2512461122.
FTIR spectra of Bennu show typical hydrated chondrite features, including silicates, OH, carbonates, and aliphatic C–H, closely resembling Ryugu. Bennu samples exhibit slightly higher CH2/CH3 ratios than Ryugu [3,4] and CM/CI chondrites. Bennu IOM displays strong aliphatic C–H along with C=O and aromatic C=C features. Higher CH2/CH3 ratios in IOM compared to intact samples suggest preferential loss of short-chain, CH3-rich compounds during solvent extraction and acid treatment.
PFY-N-XANES reveals three nitrogen bonding states: (A) imine/pyridinic N (N=C), (B) nitrile/pyridinic N, and (C) pyrrolic N/amine/amide/ammonium species (N-C,H). Intact samples show substantial heterogeneity, whereas IOM is more homogeneous and enriched in N-heterocycles. Compared to CI and CM chondrites [5], Bennu exhibits greater diversity in nitrogen functional groups. Differences between intact samples and IOM indicate that single-bonded nitrogen (N-C,H) is partly associated with soluble or acid-labile fractions.
Overall, the diversity of organic functional groups in Bennu is consistent with its rubble-pile structure and heterogeneous aqueous alteration history [6].
References:
[1] Lauretta D. et al. (2024) Meteorit. Planet. Sci. 59, 2543–2486.
[2] Glavin D. et al. (2025) Nat. Astron. 9, 199–210.
[3] Yabuta H. et al. (2023) Science 379, eabn9057.
[4] Kebukawa Y. et al. (2024) Meteorit. & Planet. Sci. 59, 1845–1858.
[5] Kebukawa Y. et al. (2025) Goldschmidt 2025, Abstract doi:10.7185/gold2025.30315.
[6] Mojarro A. et al. (2025) PNAS 122, e2512461122.