11:15 〜 11:30
[PPS03-14] Organic matter in Ryugu particles and their extracted carbonaceous residues: Evaluation by Raman spectroscopy.
キーワード：はやぶさ2、炭素質コンドライト、ラマン分光
In December 2020, a total of about 5.4 grams of material from C-type asteroid Ryugu was returned to Earth by JAXA’s Hayabusa2 spacecraft [e.g., 1]. Preliminary analyses of the returned samples showed that the Ryugu samples are most similar to CI chondrites but have lower albedo, higher porosity, and more fragile characteristics [2]. The goal of the Organic Macromolecule Initial Analysis Team is to elucidate the distributions and chemical characteristics of macromolecular organic matter in a C-type asteroid [3]. As a part of the team’s investigations, Raman characterization has been conducted independently by two groups in Japan and France on the distinct Ryugu particles.
Raman spectroscopy is a non-destructive, effective tool to assess the thermal records of carbonaceous materials. Many of the carbonaceous chondrites show the two first-order Raman bands of polyaromatic carbon materials, namely the D (“disordered”) and G (“graphite”) bands [e.g., 4]. It has been shown that D and G bands (at ~1350 and 1580 cm−1, respectively) in Raman spectra of organic matter in chondrite matrices reflect the thermal histories of the host meteorite [4-7]. Here we report our preliminary results of the Raman spectral features of the Ryugu particles obtained by the group in Japan.
Raman analyses were performed on six intact particles from Chamber A (A0108-5, -7, -17) and Chamber C (C0109-1, -15, -16) aggregates, as well as the extracted insoluble organic matter (IOM) from Chamber A (A0106) and Chamber C (C0107) aggregates [3]. Chamber A and C samples were collected at the first and second touchdown sites, respectively.
Intact grains show wide D and G bands, in addition, they are superimposed to a high fluorescence background. The intensities of the background of fluorescence in intact grains are 4 to 8 times higher than those of CM chondrites. The observed fluorescence of the extracted IOM from Ryugu aggregates is much lower than those of intact grain, however, the extracted IOM from Ryugu aggregates still shows 2 to 4 times higher fluorescence than the IOM extracted from Murchison. The significant fluorescence suggests the presence of poorly ordered carbonaceous matter [7] and may be caused by the presence of organic matter present as tiny nanoparticles [8].
Previous studies have shown that the full width, half-maximum (FWHM) of the D band decreases and the intensity ratio ID/IG increases with thermal maturity of the organic matter [e.g, 4]. In this study, wide FWHM-D and low ID/IG are observed in both intact grains and extract IOM, indicating that the Ryugu particles have largely escaped from thermal metamorphism.
Our observation based on Raman spectroscopy suggests that the fluorescence characteristics of the Ryugu particles indicate (i) a weak or lack of thermal metamorphism, and (ii) a close similarity to those of CI chondrites and Tagish Lake, which is mostly in good agreement with the results from French group [9] and FT/IR analyses [10, 11]. Additional measurements and the detailed examination for the Raman parameters between Chamber A and C aggregates are in progress.
References:[1] Tachibana et al. (2021) LPS LII, Abstract #1289. [2] Yada et al. (2021) Nat. Astron. [3] Yabuta H. et al. (2022) this meeting [4] Bonal L. et al. (2006) GCA 70, 1849–1863. [5] Busemann H et al. (2007) Meteoritics & Planet. Sci. 48, 1800–1822. [6] Bonal L. et al. (2016) GCA 189, 312–337. [7] Quirico E. et al. (2018) GCA 241, 17–37. [8] Stroud R. (2022) LPS LIII Abstract#2052. [9] Bonal L. (2022) LPS LIII Abstract#1331. [10] Kebukawa Y. et al. (2022) LPS LIII Abstract#1271. [11] Quirico E. (2022) LPS LIII Abstract#1514.
Raman spectroscopy is a non-destructive, effective tool to assess the thermal records of carbonaceous materials. Many of the carbonaceous chondrites show the two first-order Raman bands of polyaromatic carbon materials, namely the D (“disordered”) and G (“graphite”) bands [e.g., 4]. It has been shown that D and G bands (at ~1350 and 1580 cm−1, respectively) in Raman spectra of organic matter in chondrite matrices reflect the thermal histories of the host meteorite [4-7]. Here we report our preliminary results of the Raman spectral features of the Ryugu particles obtained by the group in Japan.
Raman analyses were performed on six intact particles from Chamber A (A0108-5, -7, -17) and Chamber C (C0109-1, -15, -16) aggregates, as well as the extracted insoluble organic matter (IOM) from Chamber A (A0106) and Chamber C (C0107) aggregates [3]. Chamber A and C samples were collected at the first and second touchdown sites, respectively.
Intact grains show wide D and G bands, in addition, they are superimposed to a high fluorescence background. The intensities of the background of fluorescence in intact grains are 4 to 8 times higher than those of CM chondrites. The observed fluorescence of the extracted IOM from Ryugu aggregates is much lower than those of intact grain, however, the extracted IOM from Ryugu aggregates still shows 2 to 4 times higher fluorescence than the IOM extracted from Murchison. The significant fluorescence suggests the presence of poorly ordered carbonaceous matter [7] and may be caused by the presence of organic matter present as tiny nanoparticles [8].
Previous studies have shown that the full width, half-maximum (FWHM) of the D band decreases and the intensity ratio ID/IG increases with thermal maturity of the organic matter [e.g, 4]. In this study, wide FWHM-D and low ID/IG are observed in both intact grains and extract IOM, indicating that the Ryugu particles have largely escaped from thermal metamorphism.
Our observation based on Raman spectroscopy suggests that the fluorescence characteristics of the Ryugu particles indicate (i) a weak or lack of thermal metamorphism, and (ii) a close similarity to those of CI chondrites and Tagish Lake, which is mostly in good agreement with the results from French group [9] and FT/IR analyses [10, 11]. Additional measurements and the detailed examination for the Raman parameters between Chamber A and C aggregates are in progress.
References:[1] Tachibana et al. (2021) LPS LII, Abstract #1289. [2] Yada et al. (2021) Nat. Astron. [3] Yabuta H. et al. (2022) this meeting [4] Bonal L. et al. (2006) GCA 70, 1849–1863. [5] Busemann H et al. (2007) Meteoritics & Planet. Sci. 48, 1800–1822. [6] Bonal L. et al. (2016) GCA 189, 312–337. [7] Quirico E. et al. (2018) GCA 241, 17–37. [8] Stroud R. (2022) LPS LIII Abstract#2052. [9] Bonal L. (2022) LPS LIII Abstract#1331. [10] Kebukawa Y. et al. (2022) LPS LIII Abstract#1271. [11] Quirico E. (2022) LPS LIII Abstract#1514.