Preliminary results from FTIR hyper-spectral imaging campaign on Ryugu small grains andfragments.
Zélia Dionnet1, Stefano Rubino1, Alice Aléon-Toppani1, Rosario Brunetto1, Tomoki Nakamura2, Donia Baklouti1, Zahia
Djouadi1, Cateline Lantz1, Ferenc Borondics3, Christophe Sandt3, Eva Héripré4, David Troadec5, Megumi Matsumoto2, KanaAmano2, Tomoyo Morita2, Hisayoshi Yurimoto6, Takaaki Noguchi7, Ryuji Okazaki7, Hikaru Yabuta8, Hiroshi Naraoka7,Kanako Sakamoto9, Shogo Tachibana9-10, Seiichiro 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,
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Kyushu University, Japan, 8Hiroshima University, Japan, 9ISAS/JAXA, Japan, 10The University of Tokyo, Japan, 11Nagoya
University, Japan

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Introduction: Hayabusa2 is the first sample return mission to study and return samples from a primitive carbonaceousasteroid. It thus allows the study of the same small body at very different scales, from the km down to the atomic scale. Infrared(IR) spectroscopy plays a crucial role in this respect, helping to build a bridge between the remote sensing observations of theasteroid’s surface, performed by NIRS3 [1,2] and the chemical and physical processes operating at a smaller scale andcharacterized in the laboratory on the returned samples. In December 2020, the Hayabusa2 reentry capsule delivered 5.4 g ofmaterial coming from asteroid Ryugu. This extremely precious material was then recovered by JAXA and pre-characterized
inside the ISAS curation facility [3,4]. A fraction of this material was then given to six Initial Analysis sub teams, including the“Stone” team led by T. Nakamura which studies mineralogy and petrology at a large scale [5].
Material and Methods: We will present the result of FTIR hyperspectral imaging on six micrometric Ryugu fragments(ranging from 30 to 80 µm in size). These fragments originate from 2 bigger millimetric grains (A0064 and C0046). We analyzed
these small grains in multiple configurations (see detailed analytical plan and transportation issues in [6]). After the firstcharacterization in reflectance mode on their gold substrate, we mounted these small grains at the top of metallic needles toanalyze them at different rotating angles both in transmission and reflection modes. The obtained data in transmission mode, IRCT [7] (Infrared Computed Tomography), were then analyzed to reconstruct 3D distributions of the molecular components inside
the grains, while reflectance data were projected on a 3D shape model of the grains. In this case, the fragments were treated as aplanetary surface, which will also help to reinforce the link between remote sensing and laboratories measurements. Taking
advantage of each configuration, the preliminary results of the combination of the different measurements will be shown anddiscussed.
Results and Discussion: We will present the average spectra in the 2.5 – 30 µm range. Several grains have IR signaturesat 2.7 µm, 3.0-3.1 µm, 3.4 µm, and 3.9 µm, in a good agreement with the bands identified by NIRS3 or by MicrOmega and FTIR
in the JAXA curation facility [3, 4], plus several mid-IR signatures of great interest, such as bands attributed to Si-O stretchingin phyllosilicates, and C=O stretching in organics and carbonates. A comparison of the IR spectra of the different grains withthose of a large variety of carbonaceous chondrites acquired with the same set-up will be presented. Finally, we will discuss theheterogeneity within individual grains, with particular emphasis on the following issues: (i) detection and heterogeneity of the2.7 µm band (ii) spatial correlation between phases (phyllosilicates, carbonates, opaque phases, organics) and (iii) identificationand quantification of the carbonates. These spectral observations and parameters will help to better constrain the 3D μm-scaleassembly of minerals and organics in Ryugu, and will provide information on the origin and evolution of Ryugu.
Perspectives: Our multi-analytical sequence started with non-destructive IR hyperspectral imaging and continues now
with more destructive techniques. One grain has been sliced into 3-µm thin sections and will be analyzed in 2D with higher
resolution IR hyperspectral imaging and complementary analyses [8]. The rest of the samples have been sent back to Japan, tobe analyzed at the BL47XU of SPring-8 synchrotron by XCT [9] in order to obtain complementary information concerning the3D physical, chemical and morphological properties.
Acknowledgments: We thank Moe Matsuoka for her precious help in preparing and sending Ryugu’s particles from
Sendai-Japan all the way to Orsay-France. This work is part of the multi-analytical sequence of the Hayabusa2 “Stone” MINPET group, led by Tomoki Nakamura. Zélia Dionnet was supported by a CNES postdoctoral allocation and this work wassupported by the Centre 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] Kitazato et al. 2019 Science 364-6437: 272. [2] Watanabe, S.-I., Tsuda, Y., Yoshikawa, M., et al. 2017,
Space Science Review, 208: 3. [3] Bibring et al. 2021. Metsoc Abstract #6276. [4] Yada et al. 2021. Metsoc Abstract #6186. [5]Nakamura et al. in this volume. [6] Rubino et al. in this volume. [7] Dionnet et al. 2020. Meteoritics & Planetary Science 55:
1645-1664. [8] Aléon-Toppani et al. 2021. Meteoritics & Planetary Science. [9] Tsuchiyama A. et al. 2011. Science 333-6046:1125.