Initial analysis of “stone” size Ryugu samples: current status
Tomoki Nakamura1, Megumi Matsumoto1, Kana Amano1, Yuma Enokido1, Mike Zolensky2, Takashi Mikouchi3, Yuri Fujioka1,Mizuha Kikuiri1, Eiichi Kagawa1, Daisuke Nakashima1, Adrian Brearley4, Mikhail Zolotov5, Akira Tsuchiyama6, Masayuki
Uesugi7, Yoshio Takahashi3, Moe Matsuoka8, Ralph Milliken9, Donald Brownlee10, David Joswiak10, Miki Takahashi1,
Kazuhiko Ninomiya11, Tadayuki Takahashi3, Takahito Osawa12, Kentaro Terada11, Frank E. Brenker13, Beverley Tkalcec13,Yuki Kimura14, Satoshi Tanaka8, Housei Nagano15, Rosario Brunetto16, Alice Aléon-Toppani16, Queenie Chan17, Mathieu
Roskosz18, Esen Ercan Alp19, Pierre Beck20, Aiko Nakato8, Takaaki Noguchi21, Masahiko Tanaka22, Takahiro Hiroi9, Eri
Tatsumi23, Faith Vilas24, Amanda R. Hendrix24, Camilo Jaramillo25, Gerardo Dominguez26, Cecile Engrand16, Jean Duprat16,Hidenori Genda27, Kousuke Kurosawa28, Sara Russell29, Ashley King29, Enrica Bonato30, Chi Ma31, Kentaro Uesugi7, Akihisa
Takeuchi7, Jyunya Matsuno21, Akira Miyake21, Satomi Enju32, Masahiro Yasutake7, Toru Matsumoto33, Shota Okumura21, AkiTakigawa3, Shohei Yamashita34, Takahiro Kawai3, Jean-Christophe Viennet18, Barbara Lavina19, Toshiaki Tanigaki35, KazuoYamamoto36, Deborah Domingue Lorin24, Ferenc Borondics37, Zélia Dionnet16, Donia Baklouti16, Zahia Djouadi16, Cateline
Lantz16, Stefano Rubino16, Laszlo Vincze38, Bart Vekemans38, Gerald Falkenberg39, Pieter Tack38, Ella De Pauw38, MilesLindner13, Benjamin Bazi38, Shinya Yamada40, Kenya Kubo41, Shunsaku Nagasawa3, Taiga Wada1, Satoshi Takeshita34,Akihiro Taniguchi21, Shin Watanabe3, 8, Izumi Umegaki34, Chiu I-Huan11, Yasuhiro Miyake34, Kosuke Inoue42, Seiji Sugita3,Kohei Kitasato43, Hisayoshi Yurimoto14, Ryuji Okazaki33, Hikaru Yabuta44, Hiroshi Naraoka33, Kanako Sakamoto8, Shogo
Tachibana3,8, Seiichiro Watanabe15, Yuichi Tsuda8 and the Hayabusa2-initial-analysis Stone team.
1Tohoku University, Japan, 2NASA/JSC, USA, 3The University of Tokyo, Japan, 4University of New Mexico, USA, 5Arizona State University,USA, 6Ritsumeikan University, Japan and CAS, GIG, China, 7JASRI/SPring-8, Japan, 8ISAS/JAXA, Japan, 9Brown University, USA,
10University of Washington, USA, 11Osaka University, Japan, 12Japan Atomic Energy Agency, Japan, 13Goethe University Frankfurt,Germany, 14Hokkaido University, Japan, 15Nagoya University, Japan, 16University of Paris-Saclay, France, 17University of London, UK,18Muséum National d'Histoire Naturelle, France, 19Argonne National Laboratory, USA, 20Université Grenoble Alpes, France, 21Kyoto
University, Japan, 22National Institute for Materials Science, Japan. 23 Instituto de Astrofísica de Canarias, Spain,, 24Planetary ScienceInstitute, USA, 25Pensylvania State University, 26Callfornia State University, USA, 27Tokyo tech, Japan, 28Chiba tech, Japan, 29Natural
History Museum, UK, 30Deutsches Zentrum für Luft- und Raumfahrt, Germany, 31Caltech, USA, 32Ehime University, Japan, 33Kyusyu
University, Japan, 34High Energy Accelerator Research Organization (KEK), Japan, 35Hitachi, Ltd., Japan, 36Japan Fine Ceramics
Center, Japan, 37SOLEIL Synchrotron, France, 38Ghent University, Belgium, 39DESY, Germany, 40Rikkyo University, Japan,41International Christian University, Japan, 42Kanazawa University 43University of Aizu, Japan, 44Hiroshima University, Japan.

As a part of the initial analysis of the Ryugu samples, we perform a variety of analyses of millimeter-sized "stones". Our
goals are to elucidate the entire formation process of Cb-type asteroid Ryugu from the viewpoint of petrology and mineralogy
and obtain necessary information by sample analysis, and then simulate the formation of Ryugu based on the evidence
obtained from sample analysis. Eighteen stones (8 from the chamber A and 10 from the chamber C) were received from theISAS curation facility on June 1, 2021, and placed into a fully nitrogen-displaced glove box at Tohoku University. At the sametime, we also received the powder samples from the chamber A and the chamber C. All the allocated samples were put in thesample transport containers prepared by ISAS in the nitrogen atmosphere inside the clean chamber system dedicated to Ryugu
samples. The containers were then transferred to the nitrogen glovebox at ISAS, where all the containers were completely
sealed in plastic bags with moisture and oxygen absorbers. No moisture or oxygen was detected when the bags were opened in
the glove box at Tohoku University, so it was confirmed that there was no exposure to the atmosphere during transport.
To date, a number of analyses have been carried out successfully and within schedule margins. The analysis started with themeasurement of reflectance spectra, which are sensitive to atmospheric oxidation, hydroxylation, and adsorbed water. Theultraviolet, visible, near-infrared, and mid-infrared reflectance spectra were measured while the samples were kept airtight.
The spectra of powder samples and stone samples (as aggregates and as a single stone) were successfully obtained. Concurrent
with the analyses described below were ultra-violet spectral observations on stone samples, also transported and performed in
an inert environment, conducted at the University of Illinois Urbana-Champaign (USA).
A major feature of the stone team's analysis is the use of synchrotron radiation facilities around the world. Since thisanalysis is non-destructive, stone samples whose reflectance spectra were measured were sent to KEK, SPring-8, ESRF(France), SOLEIL (France), DESY (Germany), and APS (USA). Using these synchrotron radiation facilities, high spatial
resolution and sensitivity XRD, STXM, XANES, CT [1], IR-CT, FT-IR [2, 3], XRF, and Mössbauer [4] analyses wereperformed. Most of the analyses were carried out under airtight conditions on the stone samples and the particulates separated
from the stone samples. These analyses allowed us to determine the three-dimensional distribution of solid phases andelements, redox state, density, and porosity of the stone samples.
Furthermore, as a characteristic analysis of the stone team, light elemental analysis using negative Muon was performed at theMLF facility of J-PARC with an exceptionally long allocation of machine time. This is the non-destructive method to measure
the concentration of light elements in the whole (not the surface) of stone samples. Because the characteristic X-rays produced

by muon irradiation are much higher in energy than the fluorescent X-rays produced by X-ray irradiation, there is little effectof self-absorption by the sample, and therefore, the concentration of light elements such as carbon, oxygen, and sodium in theentire "stone" sample can be determined.
Some stone samples are currently being measured for thermal conductivity and strengths in order to understand the physicalproperties of asteroid Ryugu. The data obtained from these measurements are useful for interpreting the remote-sensing data
data taken from the surface layer of the asteroid Ryugu [5-8]. It is also important for understanding the behavior of the Ryugu
material during impact events.
The surfaces of many stone samples were observed by electron microscopy and other techniques, especially on natural “flat”
surfaces formed on 5 stones. As a result, characteristric mineral aggregates formed by the reactions with water andcharacteristic impact features were observed on some samples. Based on the observations of surfaces and the synchrotronmeasurements of the whole stones, important objects such as characteristic structures and specific crystal aggregates forunderstanding the formation history of the asteroid were identified, and these parts were separated from the stone samples
using a Xe beam (pFIB) and analyzed by various methods including transmission electron microscopy and synchrotron
radiation analysis. Many stone samples, from which important objects have been separated, are embedded in epoxy resin andcut to produce many polished sections. Electron microscopy and spectroscopic measurements of the polished surfaces arebeing carried out to reveal the detailed mineralogical properties and elemental distribution inside the stone samples. In this fall,
the allocate beam time for synchrotron radiation will begin, and we plan to analyze single crystals and characteristic objects
separated from the stone samples. Photometric measurements in the ultra-violet and visible to near-infrared will also be madethis fall on the powders produced in the structural experiments to facilitate comparisons with the ONC-T and NIRS3 remotesensing observations.
Acknowledgement
We thank Drs. H. Nakao (KEK), K. Nitta (JASRI/SPring-8), O. Sekizawa (JASRI/SPring-8) for support in synchrotron
analysis and Dr. O. Sasaki for support in CT analysis at Tohoku University.
References[1] Tsuchiyama A. et al. in this volume. [2] Dionnet Z. et al. in this volume.[3] Rubino S. et al. in this volume. [4] Viennet J-C.
et al. in this volume [5] Watanabe S. et al. 2019. Science 364:268.[6] Sugita S. et al. 2019. Science 364:252. [7] Kitazato K. etal. 2019. Science 364:272. [8] Okada T. et al. 2020. Nature 579:518.