A newly revised estimation of bulk densities and examination of the shape of individual Ryugu grains

• Published in: Earth, Planets and Space
• Main Authors: Miyazaki, Akiko, Yada, Toru, Yogata, Kasumi, Hatakeda, Kentaro, Nakato, Aiko, Nishimura, Masahiro, Nagashima, Kana, Kumagai, Kazuya, Hitomi, Yuya, Soejima, Hiromichi, Tahara, Rui, Kanemaru, Rei, Nakano, Arisa, Yoshitake, Miwa, Iwamae, Ayako, Furuya, Shizuho, Tsuchiyama, Akira, Tachibana, Shogo, Michikami, Tatsuhiro, Okada, Tatsuaki, Abe, Masanao, Usui, Tomohiro
• Format: Report
• Language: English
• Published: SPRINGER 2023
• Subjects: Geology; Hayabusa2; Curation; Ryugu grains; Bulk density; 3D shapes; Geosciences; Multidisciplinary; TAGISH LAKE; POROSITY; METEORITES; SIZE; Tagish; Tagish Lake; Ryugu
• Online Access: http://ir.gig.ac.cn/handle/344008/78974; https://doi.org/10.1186/s40623-023-01904-6

The bulk density of grains from a celestial body is a fundamental property related to its composition and structure, contributing to the understanding of its evolutionary history. In this study, we provide the bulk density of 637 grains returned from the C-type near-Earth asteroid 162173 Ryugu. This is the largest number of grains to date for the curation activity, corresponding to 38 wt.% of the total returned samples (approximately 5.4 g). Although several densities of the Ryugu grains were reported, the volume estimation of some samples showed uncertainties. Therefore, we applied a new volume estimation model calibrated by X-ray micro-computed tomography (XCT) to the Ryugu grains to more accurately estimate their bulk density. The obtained average bulk density of 637 Ryugu grains was 1.79 +/- 0.31 g/cm3 (1 sigma variation) for weights of 0.5-100 mg (sub-mm -to 10 mm) irrespective of their 3D shapes characterized by three axial length ratios, considered to be a representative of the returned samples. The bulk density distributions of the grains in Chambers A and C were statistically distinguishable, with mean values of 1.81 +/- 0.30 and 1.76 +/- 0.33 g/cm3 (1 sigma variations), respectively. Despite the small difference, bulk density may have differed by sampling site. The obtained average bulk density value of A + C samples was almost the same as that of 16 Ryugu grains estimated based on CT scanned data, and was consistent with the densities of CI chondrites (1.57-1.91 g/cm3). The axial ratios of the grains in Chambers A and C were similar and those of the 724 returned samples and the flying particles ejected during the sampling operations were also similar, suggesting that relatively small Ryugu materials (mm-cm in size) are similar in shape. The minor difference between the Rygu grains and flying particles could be attributed to events such as scraping during sampling operations and transportation.