Astromaterials Science Research Group｜ISAS

【Research Highlights】 A newly revised estimation of bulk densities and examination of the shape of individual Ryugu grains

　In this study, we provided the bulk density of 637 Ryugu grains – the largest number of grains corresponding to 38 wt.% of the total returned samples to date to analyze. The average bulk density was 1.79 ± 0.31 g/cm3. The obtained bulk density was consistent with the density of a CI (Orgueil) chondrite. The bulk density distributions of the grains in Chambers A and C were statistically distinguishable though its small difference, suggesting the local bulk density variation.

　We also found that the axial ratios of the 724 returned samples (up to 10mm) and the flying particles (in few cm size) ejected during the sampling operations were similar. This suggests that relatively small Ryugu materials (mm‒cm in size) are similar in shape. The collected Ryugu samples are slightly round possibly due to the abrasion within the container during the sample return.

A) Bulk density (density of the entire particle, including both fractures and voids) of Ryugu particles plotted against weight; RG_NT indicates the density range of 16 Ryugu particles by Nakamura et al. (2022b); the green line indicates the mean value of 1.79 g/cm3. "Or" or "TL" indicates the density ranges of the Orgueil (Or) and Tagish Lake (TL) meteorites, and the letters after "_" indicates the author of the cited reference;  B) distribution of the density of Ryugu particles in each chamber (Chamber A: red, Chamber C: blue);  C) comparison between the three-dimensional shapes of Ryugu particles and flying particles.

＜From the primary author – Dr. Miyazaki＞
Taking advantage of the large number of samples that only JAXA curation can have an access to, we found differences, though small, in the bulk density distributions of the grains between Chambers A and C – this was an exciting discovery. I am grateful to the co-authors, and looking forward to the results of future research.

Original article:

Journal：  Earth, Planets and Space
Title：  A newly revised estimation of bulk densities and examination of the shape of individual Ryugu grains
Author：  Miyazaki, A. et al.
DOI：  10.1186/s40623-023-01904-6
URL：  https://doi.org/10.1186/s40623-023-01904-6
Published：  November 15, 2023

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