The Hayabusa2 Initial Analysis Team is currently engaged in analysing the sample returned from asteroid Ryugu by the Asteroid Explorer Hayabusa2 Project. The Initial Analysis Team consists of six sub-teams and two Phase-2 curation institutions, Okayama University and the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) Kochi Institute for Core Sample Research.

A summary of recent results from the Chemical Analysis Team in the Hayabusa2 Initial Analysis Team has been published in the American scientific journal, "Science", on June 10, 2022.

Initial analysis of the asteroid Ryugu sample

The sample from asteroid Ryugu returned to Earth by the asteroid explorer, Hayabusa2, on December 6, 2020, initially underwent a cataloguing description (Phase-1 curation) at the facility established at JAXA's Institute of Space and Astronautical Science. Part of the returned sample was distributed to the Hayabusa2 Initial Analysis Team, consisting of six sub-teams, and two Phase-2 curation institutes at Okayama University and JAMSTEC Kochi Institute for Core Sample Research. The initial analysis is designed to reveal the multifaceted features of the sample through a plan of high-precision analysis, with specialized sub-teams assigned to tackle the science objectives of the Hayabusa2 mission. Meanwhile, the Phase-2 curation institutes have specific specialties that are utilized to catalogue the sample based on a comprehensive analysis flow, and clarify the potential impact of the sample through measurement and analysis appropriate to the characteristics of the returned particles.

Reports from the six teams involved in the initial analysis, as well as those from Okayama University and JAMSTEC Kochi Institute for Core Sample Research, will be announced separately as the results are published in scientific journals. After the initial results have been released, a new overall summary of the Hayabusa2 science is planned.

Samples returned from the asteroid Ryugu are similar to Ivuna-type carbonaceous meteorites

1.Outline

Measurements have been conducted of the chemical and isotopic compositions of the sample returned by asteroid Ryugu by the Hayabusa2 mission. Ryugu was found to be comprised primarily of carbonaceous chondrites, especially the Ivuna-type carbonaceous chondrites known as CI chondrites. The main constituent minerals are secondary minerals that would have precipitated out from aqueous solution in the Ryugu parent body. The aqueous liquid in the parent body altered the primarily minerals that would have been originally present, and deposited the resultant secondary minerals during a time about 5 million years after the birth of the Solar System. The temperature during these changes was about 40℃, with pressures not exceeding 0.06 atm. Subsequently and to this day, the Ryugu sample is believed to not have been heated above 100℃. From these results, it can be concluded that the Ryugu sample has the most primitive characteristics without chemical differentiation of any natural sample available to humans, including the meteorites discovered so far. In the future, the Ryugu sample will be studied internationally as a new Solar System reference material.

2.Main text

The type of material that form asteroids has not yet been well understood. The first Hayabusa mission revealed that S-type asteroid is comparable to ordinary chondrite meteorites, demonstrating for the first time the direct relationship between asteroids and meteorites. Expanding on these results, Hayabusa2 conducted a sample return from the asteroid Ryugu, in order to clarify the relationship between C-type asteroids and meteorites. This paper is the first report in the series of initial analyses that were conducted.

This publication considered the (1) chemical composition, (2) isotopic composition, (3) origin of the constituents, (4) age of constituents, and (5) relationship to meteorites. Due to the wide range of research fields involved, the project is a collaboration between the Hayabusa2 Project Team, and the Astromaterials Science Research Group, as well as international teams that include prominent researchers from around the world.

X-ray fluorescence analysis, synchrotron radiation, scanning electron microscopy were used for the chemical composition analysis. Inductively Coupled Plasma Mass Spectrometry (ICP-MS), Thermal Ionization Mass Spectrometry (TIMS) and secondary ion mass spectrometry were used for the isotope analysis. The condition of the Ryugu sample used in these analyses were powder, granular, polished fragments, and chemically treated liquids.

The chemical composition of 66 elements (H, Li, Be, C, O, Na, Mg, Al, Si, P, S, Cl, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Rb, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Te, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Tl, Pb, Bi, Th, U) was determined. The Ryugu sample was found to contain contamination from Ta (tantalum). The cause of this contamination was the use of tantalum projectiles used during the sample collection by the spacecraft, was expected and proves that the projectiles successfully fired. No contamination from other elements was observed, indicating that the sample had been handled in very clean conditions.

Figure 1 shows the analytical values for each element normalized by the CI chondrite value. Variations within each element arise from the heterogeneity within the sample, due to the small sample volume (approximately 30mg) that could be used for each analysis. Considering this heterogeneity, the averages sit on an almost horizontal line across all elements, indicating that the sample has the same concentration ratios as the CI chondrites. This horizontal line sits slightly above 1.0 due to the low hydrogen (H) plot (see below for reason).

Figure 1: Elemental abundances in the Ryugu sample, normalized to the analytical values of CI chondrites. Points that sit above (below) 1.0 are elements that are present in larger (smaller) quantities than in CI chondrites (©Yokoyama et al., 2022).

The chemical composition ratio of CI chondrites is thought to reflect that of the Solar System as a whole, making Ryugu the most primitive celestial body that has retained the chemical composition of the whole Solar System since its formation.

The isotopic ratios of Ti, Cr, and O in the Ryugu sample were also shown to be similar to that of CI chondrites. Further announcements on the isotopic ratios of the other elements will be made in the future.

An image from the scanning electron microscope analysis of the Ryugu sample is shown in Figure 2. Ryugu was found to be mainly composed of phyllosilicates (serpentine (Mg, Fe)₃Si₂O₅(OH)₄ and saponite Ca_0.25(Mg,Fe)₃((Si,Al)₄O₁₀)(OH)_2·n(H₂O)). Other major minerals are dolomite CaMg(CO₃)₂, breunnerite (Mg,Fe)CO₃, pyrrhotite Fe_1-xS, and magnetite Fe₃O₄. All of these minerals are formed via precipitates from aqueous solutions. Within the interior of Ryugu's parent body, the primary minerals would have been decomposed into these secondary minerals in aqueous solutions of melting ice. This phenomenon is called aqueous alteration. Aqueous alteration was so strong in the interior of the Ryugu parent body that few primary minerals now remain. This is also very similar to that of CI chondrites.

Figure 2: Constituent minerals of the Ryugu sample. All recognizable minerals in this figure are secondary minerals that were formed by aqueous alternation within Ryugu's parent body (©Yokoyama et al., 2022).

The age and temperature at which the aqueous alteration occurred were determined by the Mn-Cr dating and oxygen isotope thermometry. About 5 million years after the birth of the Solar System, aqueous alteration developed and deposited the secondary minerals. The temperature at this time was approximately 40℃, and the lower limit on the pressure was 0.06 atm.

Later, the present-day asteroid Ryugu was formed from the meteorite parent body. After the aqueous alteration, the Ryugu sample does not appear to have been heated above 100℃ at any time until the present day. However, most of the interlayer water that was contained between the layers of phyllosilicates evaporated into space. This is the major difference between the Ryugu sample and the CI chondrites. About half the water in the CI chondrites may be the result of contamination from terrestrial water vapour. If so, the material that makes up the CI chondrites, including organic matter, may have changed significantly from their original state when they were in space. This is an important perspective for future research.

These results indicate that the Ryugu sample is similar to CI chondrites. CI chondrites consist of only a few of the tens of thousands of meteorites that exist on the Earth. Such very rare meteorites came from C-type asteroids, which are abundant in the Solar System. Moreover, Ryugu retains more chemically primitive features than that of CI chondrites. This makes the Ryugu sample a primordial sample that is chemically closer to the average composition of the Solar System that any other natural sample that we have available to us. In the future, the Ryugu sample will be used around the world as a new Solar System reference sample.

3.Paper information

Paper title:
Samples returned from the asteroid Ryugu are similar to Ivuna-type carbonaceous meteorites

Authors:
Tetsuya Yokoyama1^†, Kazuhide Nagashima^2†, Izumi Nakai³, Edward D. Young⁴, Yoshinari Abe⁵, Jérôme Aléon⁶, Conel M. O'D. Alexander⁷, Sachiko Amari⁸, Yuri Amelin⁹, Ken-ichi Bajo¹⁰, Martin Bizzarro¹¹, Audrey Bouvier¹², Richard W. Carlson⁷, Marc Chaussidon¹³, Byeon-Gak Choi¹⁴, Nicolas Dauphas¹⁵, Andrew M. Davis¹⁵,Tommaso Di Rocco¹⁶, Wataru Fujiya¹⁷, Ryota Fukai¹⁸, Ikshu Gautam1, Makiko K. Haba¹, Yuki Hibiya¹⁹, Hiroshi Hidaka²⁰, Hisashi Homma²¹, Peter Hoppe²², Gary R. Huss², Kiyohiro Ichida²³, Tsuyoshi Iizuka²⁴, Trevor R. Ireland²⁵, Akira Ishikawa¹, Motoo Ito²⁶, Shoichi Itoh²⁷, Noriyuki Kawasaki¹⁰, Noriko T. Kita²⁸, Kouki Kitajima²⁸, Thorsten Kleine²⁹, Shintaro Komatani²³, Alexander N. Krot², Ming-Chang Liu⁴, Yuki Masuda¹, Kevin D. McKeegan⁴, Mayu Morita²³, Kazuko Motomura³⁰, Frédéric Moynier¹³, Ann Nguyen³¹, Larry Nittler⁷, Morihiko Onose²³, Andreas Pack¹⁶, Changkun Park³², Laurette Piani³³, Liping Qin³⁴, Sara S. Russell³⁵, Naoya Sakamoto³⁶, Maria Schönbächler³⁷, Lauren Tafla⁴, Haolan Tang⁴, Kentaro Terada³⁸, Yasuko Terada³⁹, Tomohiro Usui¹⁸, Sohei Wada¹⁰, Meenakshi Wadhwa⁴⁰, Richard J. Walker⁴¹, Katsuyuki Yamashita⁴², Qing-Zhu Yin⁴³, Shigekazu Yoneda⁴⁴, Hiroharu Yui⁴⁵, Ai-Cheng Zhang⁴⁶, Harold C. Connolly, Jr.⁴⁷, Dante S. Lauretta⁴⁸, Tomoki Nakamura⁴⁹, Hiroshi Naraoka⁵⁰, Takaaki Noguchi²⁷, Ryuji Okazaki⁵⁰, Kanako Sakamoto¹⁸, Hikaru Yabuta⁵¹, Masanao Abe¹⁸, Masahiko Arakawa⁵², Atsushi Fujii¹⁸, Masahiko Hayakawa¹⁸, Naoyuki Hirata⁵², Naru Hirata⁵³, Rie Honda⁵⁴, Chikatoshi Honda⁵³, Satoshi Hosoda¹⁸, Yu-ichi Iijima^18‡, Hitoshi Ikeda¹⁸, Masateru Ishiguro¹⁴, Yoshiaki Ishihara¹⁸, Takahiro Iwata^18,55, Kosuke Kawahara¹⁸, Shota Kikuchi⁵⁶, Kohei Kitazato⁵³, Koji Matsumoto⁵⁷, Moe Matsuoka^18§, Tatsuhiro Michikami⁵⁸, Yuya Mimasu¹⁸, Akira Miura¹⁸, Tomokatsu Morota²⁴, Satoru Nakazawa¹⁸, Noriyuki Namiki⁵⁷, Hirotomo Noda⁵⁷, Rina Noguchi⁵⁹, Naoko Ogawa¹⁸, Kazunori Ogawa¹⁸, Tatsuaki Okada^18,60, Chisato Okamoto^52‡, Go Ono¹⁸, Masanobu Ozaki^18,55, Takanao Saiki¹⁸, Naoya Sakatani⁶¹, Hirotaka Sawada¹⁸, Hiroki Senshu⁵⁶, Yuri Shimaki¹⁸, Kei Shirai¹⁸, Seiji Sugita²⁴, Yuto Takei¹⁸, Hiroshi Takeuchi¹⁸, Satoshi Tanaka¹⁸, Eri Tatsumi⁶², Fuyuto Terui⁶³, Yuichi Tsuda¹⁸, Ryudo Tsukizaki¹⁸, Koji Wada⁵⁶, Sei-ichiro Watanabe²⁰, Manabu Yamada⁵⁶, Tetsuya Yamada¹⁸, Yukio Yamamoto¹⁸, Hajime Yano¹⁸, Yasuhiro Yokota¹⁸, Keisuke Yoshihara¹⁸, Makoto Yoshikawa¹⁸, Kent Yoshikawa¹⁸, Shizuho Furuya¹⁸, Kentaro Hatakeda⁶⁴, Tasuku Hayashi¹⁸, Yuya Hitomi⁶⁴, Kazuya Kumagai⁶⁴, Akiko Miyazaki¹⁸, Aiko Nakato¹⁸, Masahiro Nishimura¹⁸, Hiromichi Soejima⁶⁴, Ayako Suzuki⁶⁴, Toru Yada¹⁸, Daiki Yamamoto¹⁸, Kasumi Yogata¹⁸, Miwa Yoshitake¹⁸, Shogo Tachibana⁶⁵, Hisayoshi Yurimoto^10,36*

Affiliation:
¹Department of Earth and Planetary Sciences, Tokyo Institute of Technology; Tokyo 152-8551, Japan.
²Hawai'i Institute of Geophysics and Planetology, University of Hawai'i at Mānoa; Honolulu, HI 96822, USA.
³Department of Applied Chemistry, Tokyo University of Science; Tokyo 162-8601, Japan.
⁴Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles; Los Angeles, CA 90095, USA.
⁵Graduate School of Engineering Materials Science and Engineering, Tokyo Denki University; Tokyo 120-8551, Japan.
⁶Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Sorbonne Université, Museum National d'Histoire Naturelle, Centre National de la Recherche Scientifique Unité Mixte de Recherche 7590, Institut de recherche pour le développement; 75005 Paris, France.
⁷Earth and Planets Laboratory, Carnegie Institution for Science; Washington, DC, 20015, USA.
⁸McDonnell Center for the Space Sciences and Physics Department, Washington University; St. Louis, MO 63130, USA.
⁹Guangzhou Institute of Geochemistry, Chinese Academy of Sciences; Guangzhou, GD 510640, China.
¹⁰Department of Natural History Sciences, Hokkaido University; Sapporo 001-0021, Japan.
¹¹Centre for Star and Planet Formation, Globe Institute, University of Copenhagen; Copenhagen, K 1350, Denmark.
¹²Bayerisches Geoinstitut, Universität Bayreuth; Bayreuth 95447, Germany.
¹³Université de Paris, Institut de physique du globe de Paris, Centre National de la Recherche Scientifique; 75005 Paris, France
¹⁴Department of Physics and Astronomy, Seoul National University; Seoul 08826, Republic of Korea.
¹⁵Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago; Chicago, IL 60637, USA.
¹⁶Faculty of Geosciences and Geography, University of Göttingen; Göttingen, D-37077, Germany.
¹⁷Faculty of Science, Ibaraki University; Mito 310-8512, Japan.
¹⁸Institute of Space and Astronautical Science / Jaxa Space Exploration Center, Japan Aerospace Exploration Agency; Sagamihara 252-5210, Japan.
¹⁹Department of General Systems Studies, The University of Tokyo; Tokyo 153-0041, Japan.
²⁰Department of Earth and Planetary Sciences, Nagoya University; Nagoya 464-8601, Japan.
²¹Osaka Application Laboratory, Rigaku Corporation; Osaka 569-1146, Japan.
²²Max Planck Institute for Chemistry; Mainz 55128, Germany.
²³Analytical Technology Division, Horiba Techno Service Co., Ltd.; Kyoto 601-8125, Japan.
²⁴Department of Earth and Planetary Science, The University of Tokyo; Tokyo 113-0033, Japan.
²⁵School of Earth and Environmental Sciences, The University of Queensland; St Lucia QLD 4072, Australia.
²⁶Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology; Kochi 783-8502, Japan.
²⁷Department of Earth and Planetary Sciences, Kyoto University; Kyoto 606-8502, Japan.
²⁸Department of Geoscience, University of Wisconsin- Madison; Madison, WI 53706, USA.
²⁹Max Planck Institute for Solar System Research; 37077 Göttingen, Germany.
³⁰Thermal Analysis Division, Rigaku Corporation; Tokyo 196-8666, Japan.
³¹Astromaterials Research and Exploration Science Division, National Aeronautics and Space Administration Johnson Space Center; Houston, TX 77058, USA.
³²Division of Earth-System Sciences, Korea Polar Research Institute; Incheon 21990, Korea.
³³Centre de Recherches Pétrographiques et Géochimiques, Centre National de la Recherche Scientifique - Université de Lorraine; 54500 Nancy, France.
³⁴School of Earth and Space Sciences, University of Science and Technology of China; Anhui 230026, China.
³⁵Department of Earth Sciences, Natural History Museum; London, SW7 5BD, UK.
³⁶Isotope Imaging Laboratory, Hokkaido University; Sapporo 001-0021, Japan.
³⁷Institute for Geochemistry and Petrology, Department of Earth Sciences, ETH Zurich, Zurich, Switzerland.
³⁸Department of Earth and Space Science, Osaka University; Osaka 560-0043, Japan.
³⁹Spectroscopy and Imaging Division, Japan Synchrotron Radiation Research Institute; Hyogo 679-5198 Japan.
⁴⁰School of Earth and Space Exploration, Arizona State University; Tempe, AZ 85281, USA.
⁴¹Geology, University of Maryland, College Park, MD 20742, USA.
⁴²Graduate School of Natural Science and Technology, Okayama University; Okayama 700-8530, Japan.
⁴³Department of Earth and Planetary Sciences, University of California; Davis, CA 95616, USA.
⁴⁴Department of Science and Engineering, National Museum of Nature and Science; Tsukuba 305-0005, Japan.
⁴⁵Department of Chemistry, Tokyo University of Science; Tokyo 162-8601, Japan.
⁴⁶School of Earth Sciences and Engineering, Nanjing University; Nanjing 210023, China.
⁴⁷Department of Geology, School of Earth and Environment, Rowan University; Glassboro, NJ 08028, USA.
⁴⁸Lunar and Planetary Laboratory, University of Arizona; Tucson, AZ 85705, USA.
⁴⁹Department of Earth Science, Tohoku University; Sendai, 980-8578, Japan.
⁵⁰Department of Earth and Planetary Sciences, Kyushu University; Fukuoka 819-0395, Japan.
⁵¹Earth and Planetary Systems Science Program, Hiroshima University; Higashi-Hiroshima, 739-8526, Japan.
⁵²Graduate School of Science, Kobe University; Kobe 657-8501, Japan.
⁵³Department of Computer Science and Engineering, University of Aizu; Aizu-Wakamatsu 965-8580, Japan.
⁵⁴Faculty of Science and Technology, Kochi University; Kochi 780-8520, Japan.
⁵⁵The Graduate University for Advanced Studies, Sokendai, Kanagawa 240-0193, Japan
⁵⁶Planetary Exploration Research Center, Chiba Institute of Technology; Narashino 275-0016, Japan.
⁵⁷National Astronomical Observatory of Japan; Mitaka 181-8588, Japan.
⁵⁸Faculty of Engineering, Kinki University; Higashi-Hiroshima 739-2116, Japan.
⁵⁹Academic Assembly Institute of Science and Technology, Niigata University; Niigata 950-2181, Japan.
⁶⁰Department of Chemistry, The University of Tokyo; Tokyo 113-0033, Japan.
⁶¹College of Science Department of Physics, Rikkyo University; Tokyo 171-8501, Japan.
⁶²Instituto de Astrofísica de Canarias, University of La Laguna; Tenerife, Spain.
⁶³Graduate School of Engineering, Kanagawa Institute of Technology; Atsugi 243-0292, Japan.
⁶⁴Marine Works Japan Ltd.; Yokosuka 237-0063 Japan.
⁶⁵UTokyo Organization for Planetary and Space Science, University of Tokyo; Tokyo 113-0033, Japan.

^*Corresponding author. Email: yuri[at]ep.sci.hokudai.ac.jp
^†These authors contributed equally to this work.
^‡Deceased.
^§Present address. Laboratoire d'études spatiales et d'instrumentation en astrophysique, Observatoire de Paris; 92195 Meudon, France.

Journal:Science

DOI:10.1126/science.abn7850

Contact:
Tomoki Nakamura
Email: tomoki.nakamura.a8 * tohoku.ac.jp
Website: http://www.esse.epms.es.tohoku.ac.jp/project-en.html
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Posted on：June 13, 2022