11:00 〜 11:15
[PPS03-13] Unique organic matter in the asteroid Ryugu samples revealed by infrared transmission spectroscopy
キーワード：リュウグウ、はやぶさ2、初期分析、赤外分光、有機物
JAXA’s Hayabusa2 mission returned the surface samples from the carbonaceous (C-type) asteroid Ryugu. The first touchdown samples and second touchdown samples were separately stored in the sample container chamber A and chamber C, respectively. The organic macromolecule subteam started initial analysis of the Ryugu particles from June 2021, to decipher the nature of the organic matter and its origin, parent body processing, and interaction with water and minerals [1].
As a part of the organic macromolecule subteam, infrared absorption spectra from the intact Ryugu particles and extracted insoluble organic matter (IOM) were obtained using Fourier transform infrared (FTIR) microspectroscopy, to understand the nature of organic matter in Ryugu. Several samples were analyzed in parallel in the team, in Japan (Yokohama National Univ., YNU) and in France (IPAG, Grenoble and Orsay-lab teams) to increase the robustness of the analysis. The aggregates in chamber A (A0108) and chamber C (C0109) were analyzed as intact Ryugu particles. IOM was obtained after solvent extraction and HF/HCl demineralization from the aggregates A0106 and C0107 [1]. The samples were pressed between two diamond windows and then FTIR measurements were performed on the diamond windows in transmission mode.
Both in the case of intact particles and extracted IOM, the IR absorption spectra of chamber A and chamber C were almost identical, but some local heterogeneity exists. The organic features shown in the FTIR spectra of the Ryugu intact particles were aliphatic C-H stretching at 2960 cm−1 (CH3 asymmetric), 2930-2925 cm−1 (CH2 asymmetric), 2855-2850 cm−1 (CH3 and CH2 symmetric) and aromatic C=C stretching (~1600 cm−1). Carbonyl C=O stretching modes (~1700 cm−1) were not always visible. Extracted IOM displayed these peaks more clearly. In addition, C=O at 1660 cm−1 newly appeared, which may be assigned to unsaturated ketones/aldehydes or amides. The Ryugu IOM had the highest CH2/CH3 with the highest aliphatic CH/aromatic C=C ratios compared to chondritic IOM [2,3], indicating that it is rich in long chain aliphatic moieties. We also observed possible N-H features in the Ryugu IOM. The N-H absorption was previously detected from reflectance IR measurements of intact Ryugu particles by JAXA curation [4,5]. The high CH2/CH3 ratios, aliphatic-rich, and N-rich nature of Ryugu organic matter might indicate primitiveness and freshness of the Ryugu particles, which is not preserved in carbonaceous chondrites.
References: [1] Yabuta H. et al. (2022) This meeting. [2] Kebukawa Y. et al. (2011) Geochimica et Cosmochimica Acta, 75, 3530–3541. [3] Alexander C. M. O’D. (2014) Meteoritics & Planetary Science 49, 503-525. [4] Yada T. et al. (2021) Nature Astronomy. [5] Pilorget C. et al. (2021) Nature Astronomy.
As a part of the organic macromolecule subteam, infrared absorption spectra from the intact Ryugu particles and extracted insoluble organic matter (IOM) were obtained using Fourier transform infrared (FTIR) microspectroscopy, to understand the nature of organic matter in Ryugu. Several samples were analyzed in parallel in the team, in Japan (Yokohama National Univ., YNU) and in France (IPAG, Grenoble and Orsay-lab teams) to increase the robustness of the analysis. The aggregates in chamber A (A0108) and chamber C (C0109) were analyzed as intact Ryugu particles. IOM was obtained after solvent extraction and HF/HCl demineralization from the aggregates A0106 and C0107 [1]. The samples were pressed between two diamond windows and then FTIR measurements were performed on the diamond windows in transmission mode.
Both in the case of intact particles and extracted IOM, the IR absorption spectra of chamber A and chamber C were almost identical, but some local heterogeneity exists. The organic features shown in the FTIR spectra of the Ryugu intact particles were aliphatic C-H stretching at 2960 cm−1 (CH3 asymmetric), 2930-2925 cm−1 (CH2 asymmetric), 2855-2850 cm−1 (CH3 and CH2 symmetric) and aromatic C=C stretching (~1600 cm−1). Carbonyl C=O stretching modes (~1700 cm−1) were not always visible. Extracted IOM displayed these peaks more clearly. In addition, C=O at 1660 cm−1 newly appeared, which may be assigned to unsaturated ketones/aldehydes or amides. The Ryugu IOM had the highest CH2/CH3 with the highest aliphatic CH/aromatic C=C ratios compared to chondritic IOM [2,3], indicating that it is rich in long chain aliphatic moieties. We also observed possible N-H features in the Ryugu IOM. The N-H absorption was previously detected from reflectance IR measurements of intact Ryugu particles by JAXA curation [4,5]. The high CH2/CH3 ratios, aliphatic-rich, and N-rich nature of Ryugu organic matter might indicate primitiveness and freshness of the Ryugu particles, which is not preserved in carbonaceous chondrites.
References: [1] Yabuta H. et al. (2022) This meeting. [2] Kebukawa Y. et al. (2011) Geochimica et Cosmochimica Acta, 75, 3530–3541. [3] Alexander C. M. O’D. (2014) Meteoritics & Planetary Science 49, 503-525. [4] Yada T. et al. (2021) Nature Astronomy. [5] Pilorget C. et al. (2021) Nature Astronomy.