講演情報
[PPS12-P16]TOF-SIMS analysis of organic matter in Bennu samples.
*橋口 未奈子1、青木 弾1、福島 和彦1、薮田 ひかる2、癸生川 陽子3、小松 睦美4、松本 徹5、坂本 佳奈子6、榎戸 祐馬6、臼井 寛裕6、橘 省吾6,7 (1.名古屋大学、2.広島大学、3.東京科学大学、4.埼玉教育大学、5.京都大学、6.宇宙航空研究開発機構 宇宙科学研究所、7.東京大学)
キーワード：
小惑星Bennu、有機物、TOF-SIMS
Introduction: The OSIRIS-REx mission successfully returned approximately 120 g of regolith samples from the surface of the carbonaceous asteroid Bennu in September 2023 [1]. Early papers revealed the elemental and petrological characteristics of Bennu particles, which are similar to those of CI chondrites [1], and also Ryugu samples [1-2]. On the other hand, Bennu samples contain more abundant carbon, nitrogen, and ammonia than Ryugu and carbonaceous chondrites (CCs), suggesting that Bennu have experienced aqueous alteration by ammonia-rich fluids at low-temperature [3].
Our previous TOF-SIMS analysis of Ryugu samples [4-6] showed that Ryugu IOMs contain more abundant hydrocarbon ions than those of CCs (Murchison, Tagish Lake, and Orgueil). Furthermore, comparison of TOF-SIMS spectra between bulk samples and IOM samples suggested that Ryugu samples may be more susceptible to chemical structure alteration by acid treatment than CCs samples [5, 6]. In this study, we applied the same TOF-SIMS analytical protocol used for Ryugu to Bennu samples, in order to investigate their chemical structures and assess similarities and differences relative to Ryugu.
Sample and Methods: A Bennu particle (ORX-10059, ~1.4 mm) containing a yellow-bright region was crushed by a clean quartz rod, and two small fragments (ORX-10059-4-2 and -4-3) were analyzed. Fragment 10059-4-2 was divided into two pieces during mounting and was analyzed as 10059-4-2-1 and 4-2-2. Fragments were pressed onto clean Cu disks and analyzed using TRIFT V nanoTOF (ULVAC-PHI) at Knowledge Hub Aichi. Positive ion spectra were obtained using Bi32+ primary ion (30 keV, ~0.5 nA) from two areas for each fragment. The measured surface areas were 200 um x 200 um and acquisition time of about 5 min for each sample. The ion intensity of each species were normalized by using total ion intensity of signals at m/z 0 to 150 without 63 or 65Cu+ derived from Cu plate. After the TOF-SIMS analysis, mineralogical observation was performed on the sample using SEM-EDS (Hitachi SU6600) at Nagoya University).
Results and Discussion: More than 200 C-, H-, N-, O-, and S-bearing fragment ions were detected from all fragments, including hydrocarbon and heteroatom-containing ions (CHN, CHO, CHNO, etc.), consistent with previous TOF-SIMS studies of CCs and Ryugu [4-6]. Among these fragment ions, hydrocarbon and CHN-containing ions are relatively abundant in Bennu similar to Ryugu (A0106 and C0057) [5,6]. However, the relative intensities of N-containing ions (such as CHN, HNO, CNO) tends to be generally higher in Bennu than in Ryugu and also in CCs (Murchison, Tagish Lake, Orgueil). For HN-containing fragment ions such as NH3+ and NH4+, these ion intensities were highest in Orgueil, followed by Bennu ~ Tagish Lake > (or ~) Murchison > Ryugu, which consistent with their ammonia concentrations [3]. Our result likely suggests that Bennu samples contain relatively high abundances of ammonia on the surface of the sample compared with Ryugu and CCs, although at least a part of the ammonia may also be derived from IOM. We will analyze Bennu IOM in near future and will compare the results with bulk samples and Ryugu samples to clarify the origin of HN-containing fragment ions and further constrain macromolecular organic evolution of Ryugu and Bennu.
Acknowledgements
Dr. T. Uchida at Knowledge Hub Aichi, Japan for support of TOF-SIMS analysis in this study.
References:
[1] Lauretta D. S. et al. (2024) Meteorit. & Planet. Sci. 59, 2453-2486. [2] Yokoyama T. et al. (2022) Science, 379, eabn7850. [3] Glavin D. P. et al. (2025) Nature Aston. 9, 199-210. [4] Yabuta H. et al. (2023) Science 379, eabn9057. [5] Hashiguchi M. et al. (2022) Hayabusa symposium, P-14. [6] Hashiguchi M. et al. (2024) JPGU, PPS08-P12.
Our previous TOF-SIMS analysis of Ryugu samples [4-6] showed that Ryugu IOMs contain more abundant hydrocarbon ions than those of CCs (Murchison, Tagish Lake, and Orgueil). Furthermore, comparison of TOF-SIMS spectra between bulk samples and IOM samples suggested that Ryugu samples may be more susceptible to chemical structure alteration by acid treatment than CCs samples [5, 6]. In this study, we applied the same TOF-SIMS analytical protocol used for Ryugu to Bennu samples, in order to investigate their chemical structures and assess similarities and differences relative to Ryugu.
Sample and Methods: A Bennu particle (ORX-10059, ~1.4 mm) containing a yellow-bright region was crushed by a clean quartz rod, and two small fragments (ORX-10059-4-2 and -4-3) were analyzed. Fragment 10059-4-2 was divided into two pieces during mounting and was analyzed as 10059-4-2-1 and 4-2-2. Fragments were pressed onto clean Cu disks and analyzed using TRIFT V nanoTOF (ULVAC-PHI) at Knowledge Hub Aichi. Positive ion spectra were obtained using Bi32+ primary ion (30 keV, ~0.5 nA) from two areas for each fragment. The measured surface areas were 200 um x 200 um and acquisition time of about 5 min for each sample. The ion intensity of each species were normalized by using total ion intensity of signals at m/z 0 to 150 without 63 or 65Cu+ derived from Cu plate. After the TOF-SIMS analysis, mineralogical observation was performed on the sample using SEM-EDS (Hitachi SU6600) at Nagoya University).
Results and Discussion: More than 200 C-, H-, N-, O-, and S-bearing fragment ions were detected from all fragments, including hydrocarbon and heteroatom-containing ions (CHN, CHO, CHNO, etc.), consistent with previous TOF-SIMS studies of CCs and Ryugu [4-6]. Among these fragment ions, hydrocarbon and CHN-containing ions are relatively abundant in Bennu similar to Ryugu (A0106 and C0057) [5,6]. However, the relative intensities of N-containing ions (such as CHN, HNO, CNO) tends to be generally higher in Bennu than in Ryugu and also in CCs (Murchison, Tagish Lake, Orgueil). For HN-containing fragment ions such as NH3+ and NH4+, these ion intensities were highest in Orgueil, followed by Bennu ~ Tagish Lake > (or ~) Murchison > Ryugu, which consistent with their ammonia concentrations [3]. Our result likely suggests that Bennu samples contain relatively high abundances of ammonia on the surface of the sample compared with Ryugu and CCs, although at least a part of the ammonia may also be derived from IOM. We will analyze Bennu IOM in near future and will compare the results with bulk samples and Ryugu samples to clarify the origin of HN-containing fragment ions and further constrain macromolecular organic evolution of Ryugu and Bennu.
Acknowledgements
Dr. T. Uchida at Knowledge Hub Aichi, Japan for support of TOF-SIMS analysis in this study.
References:
[1] Lauretta D. S. et al. (2024) Meteorit. & Planet. Sci. 59, 2453-2486. [2] Yokoyama T. et al. (2022) Science, 379, eabn7850. [3] Glavin D. P. et al. (2025) Nature Aston. 9, 199-210. [4] Yabuta H. et al. (2023) Science 379, eabn9057. [5] Hashiguchi M. et al. (2022) Hayabusa symposium, P-14. [6] Hashiguchi M. et al. (2024) JPGU, PPS08-P12.