Small grains from Ryugu: handling and analysis pipeline for Infrared Synchrotron
Microspectroscopy
Stefano Rubino1, Zélia Dionnet1, Alice Aléon-Toppani1, Rosario Brunetto1, Tomoki Nakamura2, Donia Baklouti1, Zahia
Djouadi1, Cateline Lantz1, Obadias Mivumbi1, Ferenc Borondics3, Stephane Lefrançois3, Christophe Sandt3, Francesco
Capitani3, Eva Héripré4, David Troadec5, Megumi Matsumoto2, Kana Amano2, Tomoyo Morita2, Hisayoshi Yurimoto6,Takaaki Noguchi7, Ryuji Okazaki7, Hikaru Yabuta8, Hiroshi Naraoka7, Kanako Sakamoto9, Shogo Tachibana9-10, Sei-ichiro
Watanabe11, Yuichi Tsuda9, and the Hayabusa2-initial-analysis Stone team
1IAS, Université Paris-Saclay, CNRS, France, 2Tohoku University, Japan, 3SMIS-SOLEIL, FranceCentraleSupélec, Université Paris-Saclay, CNRS, France, 5IEMN, Université de Lille, France, 6Hokkaido University, Japan,7
Kyushu University, Japan, 8Hiroshima University, Japan, 9ISAS/JAXA, Japan, 10The University of Tokyo, Japan, 11Nagoya
University, Japan

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Introduction: In December 2020, the sample return mission
Hayabusa2 (JAXA) brought 5.4g of matter from the surface of Ctype primitive asteroid (162173) Ryugu [1]. This extremely
precious material is now the object of multiple studies with stateof-the-art techniques in laboratories all around the world (InitialAnalysis phase). These studies will grant new insight on the origin
and evolution of primitive hydrated planetesimals, and ultimately
on the early stages of our solar system. Within the Hayabusa2initial-analysis “Stone” team [1] led by T. Nakamura, we received
several microscopic particles in July 2021, with the goal ofperforming IR hyper-spectral imaging and IR micro-tomography
studies.
Samples transfer and handling: Ryugu samples are kept in acontrolled N₂ environment at Sagamihara (JAXA) in order toFigure 1. Sample-holder description
avoid exposure to the terrestrial atmosphere. We took several steps
in order to minimize the samples’ exposure to air, before, during
and after measurements. Prior to receiving the samples, we designed a custom sample-holder (Figure 1) for transferring particles
from Japan to France and for their preliminary analysis. Particles from Ruygu were deposited on a gold mirror inside the sampleholder at Tohoku University (Japan). A KBr window installed in the cover of the sample-holder allowed us to acquiremeasurements of the particles while the sample-holder was still sealed. This custom-made sample-holder was kept as clean andsterile as possible (to avoid terrestrial contamination) and it had to fulfill two major requirements: fit on the microscope stages
for our IR imaging and microspectroscopy studies and keep the samples in a dry N₂ environment (to avoid alteration from theatmosphere). The sample-holder was assembled inside a glovebox under N₂ atmosphere (ΔP ~ 6 mBar, H₂O = 1.0 ppm, O₂ = 1.2ppm). Multiple interfaces were used in order to prevent the mixing of the clean N₂ atmosphere and the ambient air (gold gasket,cleanroom static shielding bags), but also to avoid issues from shocks and vibrations (membrane boxes, foam-padded case).
Once in Sendai, the empty sample holders were opened in a glovebox, and were loaded with 32 microscopic particles from
Ryugu (distributed among four sample-holders: 14 particles from the first touchdown site in SH2 and SH3, and 18 particles fromthe second touchdown site in SH1 and SH4).
To monitor the atmosphere’s changes in our sample-holders, these were accompanied by a “control”-holder, with grains ofolivine and Fe dust (to monitor hydration and oxidation). A second “control”-holder, loaded with drierite (calcium sulfate) andsome Fe dust, was kept in France, to monitor hydration and oxidation when not under dry N₂ conditions.
Samples reception and characterization: Upon arrival at synchrotron SOLEIL (France) in early July, the sample holders wereinspected with a binocular through the KBr windows. We were able to identify at least 24 out of 32 of the original Ryugu
particles, either based on their morphological correspondence with the grains prepared at Tohoku, and/or thanks to their clear IR“Ryugu-like” spectral signatures (mainly the 2.7 µm feature [2]). The particle size range was from 20 to 80 µm, with a particularly
large particle in SH4 larger than 100 µm.
The analytical pipeline started with a full spectral characterization using the IR synchrotron beam while keeping the sampleholder closed, in order to minimize exposure to air. During the first three weeks of July, we analyzed all the identified Ryugu
grains in their sample holders using three different FTIR microscopes: (1) a mid-IR large wavelength range MCT/B-equippedand synchrotron-radiation-fed microscope, (2) a far-IR bolometer-equipped microscope, (3) an FPA-equipped imaging
microscope. Multiple detectors were used to access different wavelength ranges, covering from near-IR to far-IR (1 µm to 35µm). This large spectral coverage allowed us to detect carbonates, organics, and phyllosilicates with different band positions [3].
Most of the IR spectra showed interesting features. Hyperspectral maps in the mid-IR of the individual particles were alsoacquired, in order to assess the compositional heterogeneity at the 5-10 µm scale. A few Raman spectra and maps were alsoacquired on isolated fragments, to assess the presence and structure of endemic organics in Ryugu’s particles and to getcomplementary information on the mineralogy.

Thanks to a Raman measurement on a µm-spot on the gold substrate, we managed to detect remotely molecular oxygen inside
SH2, which indicates the holders at some point lost their air-shut condition, probably in flight from Japan to France. We estimatethat the grains were exposed to air for about 72-96 hours, before we received them and we put them again into a dry N2environment. However, we did not observe any modification of the KBr (a control KBr window we exposed to air for 24h
showed clear modifications), and the anhydrous control samples we sent along the Ryugu sample holders showed no evidenceof water adsorption nor hydration. So we inferred that Ryugu grains remained in a relatively dry environment, although inpresence of O2, probably thanks to the presence of desiccants that prevented an increase in humidity.
In mid- and late-July, we opened sample holders SH2 and SH3, and we mounted 6 Ryugu grains on W or Al needles using two
different FIB-SEM microscopes in Saclay and in Lille [4]. These grains were then measured in both transmission and reflectancemode, by Infrared Computed Tomography [5] (IR-CT) and Infrared Surface Imaging [6] (IR-SI) respectively. IR-CT allows usto assess the compositional heterogeneity of small particles in a 3D space, while IR-SI allows us to assess the surface composition
for larger particles, treating the grain as a planetary surface by projecting the 2D IR hyper-spectral maps on a 3D shape model.
Data processing and analysis of this large set of data is still ongoing. Our primary method of analysis, IR spectroscopy, is totally
non-destructive, which implies that after our measurements a few particles can be sent to other analytical teams in the scope of
combining different studies on the same sample. Some of these particles are now being analyzed by X-ray computed tomography
at SPring-8 (Japan) [7].
Overall, the outcome of the last months has shown that the agreed handling, transfer and analysis pipelines are valid and may be
applied for future sample-return missions.
Acknowledgements: We thank Moe Matsuoka for her precious help in preparing and sending Ryugu’s particles from SendaiJapan all the way to Orsay-France. This work is part of the multi-analytical sequence of the Hayabusa2 “Stone” MIN-PET group,
led by Tomoki Nakamura. Zélia Dionnet was supported by a CNES postdoctoral allocation and this work was supported by theCentre National d’Etudes Spatiales (CNES-France, Hayabusa2 mission). The micro-spectroscopy measurements were supported
by grants from Region Ile-de-France (DIM-ACAV) and SOLEIL.
References[1] T. Nakamura et al., abstract in this volume ; [2] K. Kitazato et al., Science, 2019, 364, 272–275. ; [3] Z. Dionnet et al, abstract
in this volume ; [4] A. Aléon-Toppani et al., Meteorit. Planet. Sci., 2021, 56, 1151–1172. ; [5] Z. Dionnet et al. 2020. Meteoritics& Planetary Science 55 ; [6] Z. Dionnet et al., in preparation, 2021. ; [7] A. Tsuchiyama et al., abstract in this volume.