Search

The JAXA Astromaterials Science Research Group developed a web-based database system for the Hayabusa2-returned sample from C-type asteroid Ryugu. The database (Ryugu Sample Database System; RS-DBS) is designed as an online catalog for users of wide scientific communities to choose their preferred samples and propose the sample loan through the JAXA Ryugu Sample Announcement of Opportunity. Ryugu samples can be sorted and given identification numbers as individual particles larger than 1 mm and aggregate samples consisting of less than 1 mm particle through the Phase1 curation (i.e., the initial description). The RS-DBS lists all samples with analytical data such as a microscopy image, size, weight, spectroscopic data, and shape model obtained by the initial description at the JAXA curation facility. The list also includes research results conducted by previous projects (i.e., the Hayabusa2 initial analysis team and Phase2 curation teams). The RS-DBS, built with open-source technologies, archives the data securely and long-term on the Data Archives and Transmission System (DARTS) at ISAS/JAXA.

The bulk density of grains from a celestial body is a fundamental property related to its composition and structure, providing a clue to understand the evolutionary history of the body. Here, 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 as a part of the curation activity, and corresponds to 38 wt.% of total returned samples (⁓5 g). Although several densities of the Ryugu grains were reported, some showed uncertainties in sample volume estimation. In this study, we applied a new volume estimation model calibrated by X-ray micro-computed tomography (XCT) to Ryugu grains to estimate their bulk density more accurately. The averaged bulk density of the Ryugu grains was 1.79±0.31 g/cm3 (error is 1 standard deviation) for a wide range of weight of 0.5‒100 mg (sub-mm ‒10 mm in size) and for a variety of their 3D shapes characterized by the three axial length ratios. We also found that the average bulk densities of the two sampling sites on Ryugu, stored separately in the Chambers A and C of the sample container, were almost the same within error. The log plots in the weight (≥1.0 mg) and size (≥1.5 mm) distributions were approximately linear, and the slopes were approximately -1.1 and -3.4, respectively. The average bulk density of 637 Ryugu grains with >0.5 mg was almost the same as that of 16 Ryugu grains with XCT, and also consistent with the densities of CI chondrites (1.57 ‒2.12 g/cm3). The axial ratios of the 724 Ryugu grains and the particles ejected during the sampling operations (flying particles) were similar, which suggests relatively small Ryugu materials (mm‒cm in size) are similar in shape. The minor difference between Rygu grains and flying particles could be attributed to subsequent events such as scraping during sampling operations and transportation.

Surface and subsurface materials of C-type near-Earth asteroid 162173 Ryugu were collected and successfully returned to the Earth in the Hayabusa2 mission. Fourier-Transform Infrared Spectroscopy (FTIR) has been conducted to characterize these returned samples as one of the initial description in a non-destructive manner under a purified nitrogen condition without terrestrial contamination. We selected the individual grains and aggregate samples that were not severely influenced by the reflection of incident beam at the sapphire dish and analyzed their reflectance spectra using the primary component analysis (PCA). The result indicates that Ryugu returned samples are highly homogeneous with only a little heterogeneity. The average spectrum of the main PCA group is represented by four absorption bands at 2.7, 3.05, 3.4, and 3.95 µm. The spectral feature is consistent with that obtained from bulk FTIR measurements as reported in Yada et al. (2022), indicating potential presence of hydroxyl, organics and carbonates. Rarely observed types of grains with unique spectra are categorized into three groups: significantly high reflectance, carbonates, and hydroxyl compounds.

C-type asteroids likely formed in the outer Solar System and were then scattered inwards during giant planet migration (Walsh et al., 2011). They may have transported volatiles to the inner Solar System and created the conditions suitable for life on Earth(Alexander, 2017). Carbonaceous chondrites are fragments from C-type asteroids and provide evidence that these generally organic-rich (Garvie and Buseck, 2007) bodies experienced extensive aqueous alteration early in Solar System history (Alexander et al., 2014). On 6th December 2020, ~5.4g of material was delivered to Earth from the C-type asteroid 162173 Ryugu by the Hayabusa2 spacecraft (Yada et al., 2021). Here we present the results of an integrated bulk and micro-analytical study of Ryugu particles, which provides a unique insight into the interrelationship between aliphatic-rich organics and surrounding hydrous minerals at a sub-micrometer scale. This dataset has clear implications for better understanding the origin and early evolution of Solar System organic matter and demonstrates that Ryugu particles are among the most uncontaminated extraterrestrial materials so far studied.

C-type asteroids are considered to be primitive small Solar-System bodies enriched in water and organics, providing clues for understanding the origin and evolution of the Solar System and the building blocks of life. C-type asteroid 162173 Ryugu has been characterized by remote sensing and on-asteroid measurements with Hayabusa2, but further studies are expected by direct analyses of returned samples. Here we describe the bulk sample mainly consisting of rugged and smooth particles of millimeter to submillimeter size, preserving physical and chemical properties as they were on the asteroid. The particle size distribution is found steeper than that of surface boulders11. Estimated grain densities of the samples have a peak around 1350 kg m-3, which is lower than that of meteorites suggests a high micro-porosity down to millimeter-scale, as estimated at centimeter-scale by thermal measurements. The extremely dark optical to near-infrared reflectance and the spectral profile with weak absorptions at 2.7 and 3.4 microns implying carbonaceous composition with indigenous aqueous alteration, respectively, match the global average of Ryugu, confirming the sample’s representativeness. Together with the absence of chondrule and Ca-Al-rich inclusion of larger than sub-mm, these features indicate Ryugu is most similar to CI chondrites but with darker, more porous and fragile characteristics.