16:15 〜 16:30
[PCG20-10] Hayabusa2 Initial Analysis of Macromolecular Organic Matter in the Asteroid Ryugu Samples
キーワード：はやぶさ２、小惑星リュウグウ、固体有機物
Introduction: JAXA’s Hayabusa2 mission explored the carbonaceous asteroid Ryugu and collected its sands and pebbles for investigating the origins of planets and life, [1]. On December 6, 2020, the asteroid sample was returned to the Earth. Through the curatorial work at JAXA, it was reported that the Ryugu samples contain high abundances of hydrous minerals and organics [2, 3]. Afterward, the initial sample analysis has started from June 2021 to classify and characterize the Ryugu samples in the context of the Solar System formation. The Organic Macromolecule Initial Analysis Team aims to unveil the elemental, isotopic, and functional group compositions, structures and morphologies of macromolecular organic matter from the Ryugu samples [4].
Samples and Methods: Chamber A aggregates (A0108) and Chamber C aggregates (C0109) collected at the first and second touchdown sites, respectively, have been analyzed. Additional aggregates from Chamber A (A0106) and Chamber C (C0107) were treated with HCl and HCl/HF to yield insoluble organic matter (IOM).
The analytical procedures included a combination of micro-Fourier transform infrared microspectroscopy (μ-FTIR), micro-Raman spectroscopy, synchrotron-based scanning transmission X-ray microscopy coupled with X-ray absorption near edge structure (STXM-XANES), scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDS), atomic force microscope based infrared spectroscopy (AFM-IR), and nanometer-scale secondary ion mass spectrometry (NanoSIMS).
Results and discussion: The broad Raman D- and G-bands observed from the Ryugu intact grains reflected that organic matter in the asteroid samples has a disordered, polyaromatic structure [5, 6]. Characteristically, the Ryugu samples had high fluorescence background, which is similarly observed in CI chondrites. The Raman spectral parameters show that the Ryugu samples escaped thermal metamorphism on the parent body. The μ-FTIR [7-9] and STXM-XANES [10] analyses of the Ryugu grains showed that organic matter in the asteroid samples is a complex macromolecular solid consisting of aromatic carbon, aliphatic carbon, ketones and carboxyls. Combination of STXM-XANES [10], STEM [11], and AFM-IR [12] revealed that the organic functional group compositions correlate with the morphologies of nano-sized organic matter. Organic nanoglobules are aromatic-rich, while organic matter in Ryugu matrix was IOM-like or diffuse carbon. These organic microstructures were associated with Mg-rich phyllosilicates and carbonates, and thus the observed functional group diversity likely resulted from aqueous alteration on the asteroid parent body. This conclusion is also supported by NanoSIMS measurements showing the hydrogen isotopic distributions of the Ryugu IOM within the range of CI, CM, and Tagish Lake chondrites as well as the similar δ15N values of IOM between the Ryugu samples and CI chondrites [13]. Additionally, some of the individual carbonaceous grains showing extreme D and/or 15N enrichments or depletions could possibly have been derived from the solar nebula or protosolar molecular cloud [14, 15].
References: [1] Tachibana S. et al. (2022) Science, doi: 10.1126/science.abj8624. [2] Yada T. et al. (2021) Nat. Astron. doi.org/10.1038/s41550-021-01550-6. [3] Pilorget C. et al. (2021) Nat. Astron. doi.org/10.1038/s41550-021-01549-z. [4] Yabuta et al. 53rd Lunar Planet Sci., [5] Bonal et al. 53rd Lunar Planet Sci., [6] Komatsu et al. 53rd Lunar Planet Sci., [7] Kebukawa et al. 53rd Lunar Planet Sci., [8] Quirico et al. 53rd Lunar Planet Sci., [9] Dartois et al. 53rd Lunar Planet Sci., [10] De Gregorio et al. 53rd Lunar Planet Sci., [11] Stroud et al. 53rd Lunar Planet Sci., [12] Mathurin et al. 53rd Lunar Planet Sci., [13] Remusat et al. 53rd Lunar Planet Sci., [14] Barosch et al. 53rd Lunar Planet Sci., [15] Nittler et al. 53rd Lunar Planet Sci.
Samples and Methods: Chamber A aggregates (A0108) and Chamber C aggregates (C0109) collected at the first and second touchdown sites, respectively, have been analyzed. Additional aggregates from Chamber A (A0106) and Chamber C (C0107) were treated with HCl and HCl/HF to yield insoluble organic matter (IOM).
The analytical procedures included a combination of micro-Fourier transform infrared microspectroscopy (μ-FTIR), micro-Raman spectroscopy, synchrotron-based scanning transmission X-ray microscopy coupled with X-ray absorption near edge structure (STXM-XANES), scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDS), atomic force microscope based infrared spectroscopy (AFM-IR), and nanometer-scale secondary ion mass spectrometry (NanoSIMS).
Results and discussion: The broad Raman D- and G-bands observed from the Ryugu intact grains reflected that organic matter in the asteroid samples has a disordered, polyaromatic structure [5, 6]. Characteristically, the Ryugu samples had high fluorescence background, which is similarly observed in CI chondrites. The Raman spectral parameters show that the Ryugu samples escaped thermal metamorphism on the parent body. The μ-FTIR [7-9] and STXM-XANES [10] analyses of the Ryugu grains showed that organic matter in the asteroid samples is a complex macromolecular solid consisting of aromatic carbon, aliphatic carbon, ketones and carboxyls. Combination of STXM-XANES [10], STEM [11], and AFM-IR [12] revealed that the organic functional group compositions correlate with the morphologies of nano-sized organic matter. Organic nanoglobules are aromatic-rich, while organic matter in Ryugu matrix was IOM-like or diffuse carbon. These organic microstructures were associated with Mg-rich phyllosilicates and carbonates, and thus the observed functional group diversity likely resulted from aqueous alteration on the asteroid parent body. This conclusion is also supported by NanoSIMS measurements showing the hydrogen isotopic distributions of the Ryugu IOM within the range of CI, CM, and Tagish Lake chondrites as well as the similar δ15N values of IOM between the Ryugu samples and CI chondrites [13]. Additionally, some of the individual carbonaceous grains showing extreme D and/or 15N enrichments or depletions could possibly have been derived from the solar nebula or protosolar molecular cloud [14, 15].
References: [1] Tachibana S. et al. (2022) Science, doi: 10.1126/science.abj8624. [2] Yada T. et al. (2021) Nat. Astron. doi.org/10.1038/s41550-021-01550-6. [3] Pilorget C. et al. (2021) Nat. Astron. doi.org/10.1038/s41550-021-01549-z. [4] Yabuta et al. 53rd Lunar Planet Sci., [5] Bonal et al. 53rd Lunar Planet Sci., [6] Komatsu et al. 53rd Lunar Planet Sci., [7] Kebukawa et al. 53rd Lunar Planet Sci., [8] Quirico et al. 53rd Lunar Planet Sci., [9] Dartois et al. 53rd Lunar Planet Sci., [10] De Gregorio et al. 53rd Lunar Planet Sci., [11] Stroud et al. 53rd Lunar Planet Sci., [12] Mathurin et al. 53rd Lunar Planet Sci., [13] Remusat et al. 53rd Lunar Planet Sci., [14] Barosch et al. 53rd Lunar Planet Sci., [15] Nittler et al. 53rd Lunar Planet Sci.