R5: Extraterrestrial materials

[R5-06] Analytical X-ray nanotomography of carbonaceous chondrites and their heated samples as a rehearsal of Hayabusa2 sample analysis.

[Presentation award entry]

*Mingqi Sun^1,2, Akira Tsuchiyama^3,2, Megumi Matsumoto¹, Yuri Fujioka¹, Tomoki Nakamura¹, Junya Matsuno³, Akira Miyake⁴, Naotaka Tomioka⁵, Motoo Ito⁵, Yu Kodama⁶, Naoto Nakano⁴, Stefano Rubino⁷, Kentaro Uesugi⁸, Akihisa Takeuchi⁸, Masahiro Yasutake⁸ (1. Tokoku Univ. Sci., 2. GIG, CAS, 3. Ritsumeikan Univ., 4. Kyoto University, 5. KICSR/JAMSTEC, 6. Marine Works Japan Ltd., 7. Inst. Astrophys. Spat. U. Paris-Saclay, 8. SPring-8/JASRI)

Keywords:Ryugu, nano X-CT, chondrite

The Hayabusa2 spacecraft has successfully returned to Earth on 6^th of Dec. 2020, carrying samples of the C-type near-Earth asteroid 162173 Ryugu. It is highly expected that the samples are similar to carbonaceous chondrites (CCs), which play a significant role in water and organic material delivery to the earth. SR-based X-ray nanotomography (SR-XCT) is a powerful technique to characterize nondestructively the detailed 3D structures in particular for CCs which have fine matrix. We performed SR-XCT analyses at BL47XU of SPring-8 synchrotron facility. SR-XCT acquires a nondestructive three-dimensional (3D) structure including external shapes and constituent phases with high signal-to-noise ratios and high spatial resolution (~100 nm). We can discriminate mineral phases and organic materials from the linear attenuation coefficients (LACs) and x-ray refractive index decrement (RIDs), which is almost proportional to material density, in phase shift images. This method could be beneficial to recognize the mineralogical features and estimate the heated condition of the asteroid Ryugu samples. We analyzed 34 samples by the DET-SIXM method to small particles of different groups of carbonaceous chondrites to understand variations in the same meteorites and among different groups. We obtained the peaks of the 3D histogram of the two LAC values at 7 and 7.35 keV and RID values as the representatives of the constituent materials in each sample grain. The first peaks generally come from the matrix of the meteorites, which is mainly composed of Fe-Mg hydrous silicates .We can estimate the Mg#, degree of dehydration and porosity of matrix from the 3D peak positions. Based on the results of the 3D peak analysis, it is concluded that (1) we may recognize the carbonaceous chondrite groups, CM, CI and C-ungrouped, (2) we can recognize samples heated at temperatures larger than ~500^oC, (3) heated samples could experience two processes: Fe-enrichment and dehydration and (4) this method is not so sensitive to estimate heating duration at least at 600^oC.