A first look at the interior and exterior of Ryugu preserved in samples collected by Hayabusa2
Eizo Nakamura1, Katsura Kobayashi1, Ryoji Tanaka1, Tak Kunihiro1, Hiroshi Kitagawa1, Christian Potiszil1, Tsutomu Ota1,
Chie Sakaguchi1, Masahiro Yamanaka1, Yusuke Yati1,Tomohiro Usui2, Yuichi Tsuda2, Seichiro Watanabe3, Masanao Abe2,
Tatsuaki Okada2, Toru Yada2
1
The Pheasant Memorial Laboratory, Inst. for Planetary Materials, Okayama Univ. at Misasa, Tottori 682-0193, Japan.
2Inst. Space Astronaut. Sci., Japan Aerosp. Explor. Agency (JAXA), Kanagawa 252-5210, Japan
3
Dept Earth Planet. Sci., Grad. Sch. Sci., Nagoya Univ., Nagoya 464-8601, Japan.
Sample return missions represent great opportunities to study materials from known locations. The Hayabusa mission returnedmaterial to Earth from the asteroid Itokawa in 2010 and revealed through geochemistry and micro-petrograpy that it isgenetically related to ordinary chondrite meteorites and the surface of the modern-day asteroid is being actively bombarded byhyper-velocity small particles (e.g., Kawaguchi et al., 2003; Nakamura et al., 2012). The Hayabusa2 mission returned material
to Earth from Ryugu on 6th of December, 2020 (Tsuda et al., 2020). Based on the very low geometric albedo indicated byremote observations (Sugita et al., 2019; Kitazato et al., 2019), abundant organic matter on Ryugu, compared to those incarbonaceous chondrites, might be expected (Potiszil et al., 2020). The initial uncontaminated and non-destructive
observations for the entire set of returned samples in the Phase-1 Curation at JAXA/ISAS (Yada et al., 2021) demonstrated
that Hayabusa2 retrieved the representative and unprocessed (albeit slightly fragmented) Ryugu sample. The data further
expanded on the indications from the remote sensing observations that Ryugu is dominated by hydrous carbonaceouschondrite-like materials, similar to CI chondrites, but with an optically darker, more porous, and more fragile nature.
In order to analyze both organic and inorganic matter, the pieces of Ryugu were subject to in-depth investigations in thePheasant Memorial Laboratory (PML), Okayama University at Misasa. The 16 particles of Ryugu sample (A0022, A0033,A0035, A0048, A0073, A0078, and A0085 from the natural surface of the equatorial region of Ryugu, and C0008, C0019,C0027, C0039, C0047, C0053, C0079, C0081, and C0082 from the surrounding site of the artificial impact crater on Ryugu;
total ~55 mg) were selected during the Phase-1 Curation. The selected samples were then transferred to the ultimate clean
room in the PML for Phase-2 Curation, to catalog the samples via a comprehensive analytical strategy.
The particles were first characterized under digital optical microscope and then their volume and mass were measured
to determine their densities. The average density was 1530 ± 250 kg m-3, which was systematically larger than the value
reported in Yada et al (2021). To elucidate the systematic differences among the 16 pieces, both plainer surfaces and powder
were created from each piece using an ultra-microtome equipped with a diamond knife. The surface was observed using
optical microscope and SEM, the major element distribution and mineral phases were determined by EDS installed in SEM,
micro-Raman spectroscopy, micro-XRD and TEM, all without coating. Subsequently, major and trace element compositions
were determined from a given powder by ICP-MS. Element and isotope compositions of H, C, N and O were determined bygas-source mass-spectrometry, and those of Ne were determined by laser-heating noble-gas-mass-spectrometry using small
broken pieces. Solvent soluble organic matter was extracted from sample powders using various solvents, including water,acetonitrile, ethyl acetate and formic acid. Meanwhile, insoluble organic matter was isolated after solvent extraction anddemineralization by HCl, HF and boric acid. After the first-round characterization, the microtomed surfaces were surveyedusing micro-Raman spectroscopy, SIMS and desorption electrospray ionization-orbitrap-mass spectrometry (DESI-OT-MS).
The 16 pieces were found to consist of magnetite, carbonate, phosphates, sulfides and minor silicate fragmentsinterfiled by matrix (modal abundance of 86-96%) that was dominated by sub-micron-sized phyllosilicates. Average modalabundances of the aforementioned phases (excluding matrix) were 3.7, 2.4, 0.8, 2.5 and 0.4 %, respectively. The
phyllosilicates were mainly composed of the serpentine and smectite groups. As noted by the Phase-1 Curation, the existenceof high-temperature nebular products, such as refractory inclusions and chondrules were not found. The magnetite was present
as micron-sized euhedral to subhedral grains and sub-micron-sized grains with a framboidal and plaquette texture. Noncarbonate carbon-rich phases of several micrometers in size, were discovered embedded in the matrix (modal abundance is~0.2%). The presence of soluble and insoluble organic matter was confirmed by DESI-OT-MS and FTIR and micro-Raman
spectroscopy, respectively. Further characterization of the solvent soluble fraction via HPLC-OT-MS and GC-MS is currently
underway. The organic matter is ubiquitous in the matrix according to observations by SIMS and micro-Raman spectroscopy.

The major and trace element compositions and O isotope composition are homogenous, with the major and traceelement compositions representing the proto-solar abundance of Lodders (2020). However, a significant variation of H, C, Nand Ne isotopic compositions at the sub-mm scale among the particles was found, which suggests that Ryugu has experienced
a complex evolutionary history.
In this talk, preliminary results from the Misasa Phase2 Curation team will be presented.
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