Asteroid Explorer Hayabusa2 Initial Analysis Stone Team reveals Formation and<br />evolution of the carbonaceous asteroid Ryugu.

Asteroid Explorer Hayabusa2 Initial Analysis Stone Team reveals Formation and
evolution of the carbonaceous asteroid Ryugu.

The Japan Aerospace Exploration Agency (JAXA) has just completed the first year of its analytical campaign on samples returned from asteroid Ryugu. These cutting-edge studies have been undertaken by six sub-teams of the Initial Analysis Team and two Phase-2 curation teams. We are pleased to announce that a paper summarizing the research results of the "Stone Analysis Team" of the Hayabusa2 Initial Analysis Team has been published in the American scientific journal "Science" on September 23, 2022.

Title	Formation and evolution of the carbonaceous asteroid Ryugu: Direct evidence from return samples
Journal	Science
DOI	10.1126/science.abn8671

Initial Analysis of Asteroid Ryugu Samples

The samples 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. The initial analysis team 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's mission. Meanwhile, the Phase-2 curation institutes have specific specialties that are utilized to catalog the samples 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 two Phase-2 curation institutes, will be announced separately as the results are published in scientific journals. After all the initial results have been released, a new overall summary of the Hayabusa2 science is planned.

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Formation and evolution of carbonaceous asteroid Ryugu:
Direct evidence from returned samples

Key points of the paper

∗ We found that Ryugu samples contain particles (such as Ca- and Al-rich inclusions ¹⁾ that were formed in high-temperature environments (>1000℃). These high-temperature particles are thought to have formed near the Sun and then migrated to the outer solar system, where Ryugu was formed. This indicates that large-scale mixing of materials occurred between the inner and outer solar system at the time of its birth.
∗ Based on the detection of the magnetic field left in the Ryugu samples, it is highly likely that the original asteroid from which the current Ryugu descended (Ryugu's parent body ²⁾) was born in the darkness of nebular gas ³⁾, far from the Sun, where sunlight cannot reach.
∗ Liquid water trapped in a crystal in the sample was discovered. This water was carbonated water containing salts and organic matter, which was once present in the Ryugu parent body.
∗ Crystals shaped like coral reefs were growing from the liquid water that existed in the interior of Ryugu's parent body.
∗ In the parent body of Ryugu, the ratio of water to rock differed between the surface and the interior, with rocks deeper underground containing more water.
∗ The hardness, heat transfer, and magnetic properties of the samples were measured. The results showed that the Ryugu sample was soft enough to be cut with a knife. The sample also contained many small magnets, behaving like a natural hard-disk, recording the magnetic field of the past.
∗ A computer simulation of the process from the birth of the Ryugu parent body to its destruction by a catastrophic impact was performed. This is the first time that measurements of the hardness and thermal diffusivity of actual asteroid samples have been incorporated into a simulation of the formation and evolution of asteroids.
∗ The simulation shows that the Ryugu parent body accumulated about 2 million years after the formation of the solar system, and then heated up to about 50℃ over the next 3 million years, resulting in chemical reactions between water and rock The size of the impactor that destroyed the Ryugu parent body, which is about 100 km in diameter, is at most 10 km in diameter, and that the present-day Ryugu is composed of material from a region far from the impact point.

Summary of the paper

A research group led by Professor Tomoki Nakamura at the Graduate School of Science, Tohoku University analyzed samples from the asteroid Ryugu recovered by the asteroid explorer Hayabusa2 (17 particles including the third largest sample recovered by the explorer (Figure 1)) using cosmochemical and physical methods at universities and institutes including five synchrotron radiation facilities in Japan, United States, and Europe. As a result, the history of Ryugu from its formation to its collisional destruction (i. e., formation and location in the solar system, information on the source material, types of ice contained, chemical evolution through reactions with water on the surface and in the interior of the asteroid, effects of collisions, etc.) were determined. The Ryugu samples were found to contain a mixture of material near the surface of the parent body before impact destruction and material from the interior of the body. The hardness, heat transfer, specific heat, density, etc. of the Ryugu samples were measured, and numerical simulations of the temperature change due to heating in the interior of the parent body and the impact destruction process of the body were performed using these measured physical values to reproduce the formation evolution of Ryugu on a computer.

Detailed description of the paper

The formation history of Ryugu, as determined from the analysis of Ryugu samples, can be divided into the six phases shown below. Figure 2 show the results of the numerical simulation using the analysis results.

1. Formation of the Ryugu parent body,
2. Melting of ice due to decay heat of radioactive elements,
3. Progression of water-rock reactions due to further increase in the internal temperature of the body,
4. Cooling of the body due to depletion of radioactive elements,
5. Destruction of the parent body by a large-scale collision event,
6. Formation of Ryugu by reassembly of rock fragments generated by the collision.

The evidence for each of these stages of formation was obtained from Ryugu samples, as shown below.

Birth of the parent body of Ryugu

• Based on the remanent magnetization in the samples, it is highly likely that Ryugu's parent body was born in the primordial solar nebula³⁾, which does not exist today. Ryugu was born in the darkness of nebular gas far from the sun, where sunlight cannot reach.

• The Ryugu parent body was born at an extremely low temperature of -200℃ or lower. In that region, not only water ice but also dry ice (CO₂ ice) existed. The Ryugu parent body was formed by incorporating the rock particles and ice that existed in the region.

• We found particles (such as Ca- and Al-rich inclusions ¹⁾) that were formed at high temperatures near the Sun (Fig. 3). The newly-born Ryugu contained, in addition to the low-temperature materials (ice and dry ice), a small amount of materials formed at high temperatures near the sun. These high-temperature particles are thought to have migrated from near the Sun to the outer solar system. This is evidence of a large-scale mixing of materials between the inner and outer solar system at the time of its birth.

• The chemical composition of 10 particles of the Ryugu samples (126 mg in total) was determined for light elements using a muon⁴⁾ beam (@J-PARC). The abundance of the light elements nitrogen and carbon is close to that of the most primitive meteorite (CI carbonaceous chondrites), indicating that the elemental abundance of Ryugu is very primitive.

Reactions between rocks and liquid water after the formation of the Ryugu parent body

• The raw materials of Ryugu were ice and various aggregates of solid particles (Figures 2 and 4). These raw materials reacted with water and CO₂ in the interior of the parent body (aqueous alteration) to form hydrous silicates and carbonate minerals that make up the majority of the sample.
The water temperature during aqueous metamorphism is estimated to have been approximately 25℃ based on the stability of the minerals formed during aqueous alteration.

• Liquid water trapped in crystals in the sample was found (Figure 5). The water was held in micron-sized vacancies. Molecular species were determined by mass spectrometry, and the water was carbonated containing salts and organic matter.

• The Ryugu sample was composed of small rock fragments (~1 mm in diameter). The diversity of minerals in these rock fragments can be explained by the different conditions for chemical reactions with water.

• The rock fragments can be divided into two main types: materials formed in environments with a low water content (water/rock mass ratio ‹ 0.2) and materials formed in environments with a high water content (0.2 ‹ water/rock mass ratio ‹ 0.9). The former is rock fragments formed near the surface of the parent body where it was easy to cool and ice was difficult to melt (Figure 4), and the latter is considered to be material formed in the interior of the parent body. Therefore, the present-day Ryugu contains a mixture of materials from the surface and interior of its parent body.

• In the interior of Ryugu's parent body, tabular coral-like crystals grew from liquid water (Fig. 6), suggesting that an environment similar to the Earth's oceans existed in Ryugu's interior.

Physical Properties of Ryugu Sample Formed through Reaction with Water

• Physical properties (hardness, heat transfer, specific heat, density, etc.) of the Ryugu samples were measured. The volume of the samples was precisely determined by synchrotron radiation CT analysis (@SPring-8) with a spatial resolution of less than 1 micron, and the mass was measured in an environment with no atmosphere to avoid the influence of adsorbed water on the samples. The average density of the sample was 1.79 ± 0.08 g/cm³, which is much higher than the density of the entire Ryugu asteroid (1.19 g/cm³). This suggests that interior of Ryugu contains more than 30% of pore spaces.

• The hardness of Ryugu's samples is very low compared with that of igneous rocks on Earth, making them soft. The Ryugu stones were actually easily cut using a blade.

• The Ryugu sample contains a large amount of magnetite, and a characteristic distribution of magnetic field lines (spiral magnetic domain structure: Figure 7) was confirmed in the interior of these crystals. This structure is more stable than ordinary hard disks and can record magnetic fields for more than 4.6 billion years. The magnetic fields inside and around magnetite record the magnetic field at the time when these crystals were formed, and it is highly likely that the solar nebula (with a magnetic field) was present when the Ryugu parent body was formed.

Numerical simulation of the thermal history and the collisional destruction of the Ryugu parent body

• The authors have succeeded in reproducing the history of Ryugu from the birth of the parent body to the disruption of the parent body via a large-scale collision using a computer. This is the first time that the results of hardness and thermal diffusivity of an actual asteroid sample are used to simulate the formation and evolution of an asteroid.

• A numerical simulation of the temperature change inside the asteroid due to the heat of decay of radioactive elements was performed. As a result, we were able to reproduce the process from the formation of the Ryugu parent body in an environment below -200℃ about 2 million years after the formation of the solar system, to the start of the water-rock reaction about 3 million years later, to the maximum temperature (~50℃) reached inside the body about 5 million years later, to the formation of the present Ryugu's constituent materials.

• We performed numerical simulations of the collisional destruction of the parent body of Ryugu. It is thought that Ryugu once belonged to either the Polarna or Eularia family ⁵⁾ of asteroid families ⁶⁾, and that all asteroids belonging to these families were formed by the destruction of Ryugu's parent body. Based on this inference, the Ryugu parent body would have had a diameter of about 100 km. When another body with a diameter about 1/10th of the parent body collides with the parent body, the parent body is destroyed, forming a body with a maximum diameter of ~50 km (about the same size as Polana and Eularia) and numerous small rock fragments. The present-day Ryugu is thought to have been formed by the reassembly of some rock fragments produced by the collision.

• Simulations of collisional disruption indicate that high pressures and temperatures are reached only near the epicenter of impact (only about 0.2 volume % of the parent body experiences impact pressures of 10 GPa or higher), and the majority of the parent body breaks up without experiencing high pressures and temperatures. We found little evidence of strong impacts in the Ryugu samples. This indicates that the rock fragments that formed the present-day Ryugu are materials that originated distant from the epicenter of the collision with Ryugu's parent body.

• The present-day Ryugu is thought to have been formed through the above processes (Figure 2). Water-bearing asteroids such as Ryugu are more widely distributed in the solar system than water-free objects. This study shows how such asteroids formed, evolved, were collisionally destroyed to their present form in the low-temperature region outside Jupiter, far from the Sun. This has provided a pathway to solutions to some of the many unresolved questions regarding the formation of the solar system.

• This research was supported by Grant-in-Aid for Scientific Research (20H00188 and 21H00159), of which Nakamura is a principal investigator, and many separate grants to coinvestigators by other agencies.

Fig.1(A) Optical micrograph of the largest sample C0002 analyzed and (B) CT view of the interior of the sample obtained by synchrotron radiation X-ray CT analysis at SPring-8. It can be seen that the entire sample is composed of fine-grained material (gray). (Credit: SPring-8, Tohoku Univ.)

Fig.2: Ryugu formation and evolution process inferred from the analysis of Ryugu samples. The temperature distribution, age, and collisional destruction process of the object were obtained by numerical simulation. (Credit: MIT, Chiba Tech, Tokyo Tech, Tohoku Univ.)

Figure 3: Particles formed in high temperature environments (>1000℃) found in the Ryugu samples (all images are taken by electron microscopes). (A, B) Ca- and Al-rich inclusions, (B-D) chondrules ⁷⁾ consist of olivine (Ol), metallic iron (FeNi), and iron sulfide (FeS), (F) porous particles resembling amoeboid olivine aggregates. (Credit: Tohoku Univ)

Fig. 4: Rock fragments found in the C0002 sample that retain primitive features before aqueous alteration (images taken by electron microscopes). (A) Overall view of the fine-grained, porous rock fragment. (B) magnified view of a portion of the rock fragment. (C) elemental distribution in the same area as in B. Red particles indicate olivine or pyroxene, indicating that these minerals are abundant. (D) Overall view of a fine-grained, porous rock fragment. (E) magnified view of a portion of D. The main constituents are amorphous silicate and iron sulfide particles less than 1 micron in size (indicated as GEMS-like in the photograph), and olivine (Ol). (Credit: Tohoku Univ.)

Figure 5: Liquid consisting mainly of water and CO₂ found inside a hexagonal iron sulfide crystal (iron sulfide) in a Ryugu sample. (A, B) CT images of vacancies in iron sulfide crystals. (C) Various ion species contained in the vacancies as measured by mass spectrometer (the two pictures of the same molecular species show the ion species contained in the upper part of the vacancy on the left and in the middle part on the right). The crystal temperature was set to -120℃ and the liquid in the vacancies was frozen for analysis. (D) After the analysis, the liquid in the vacancies was evaporated and the interior of the vacancies was observed. The results indicate that there are no solid components other than the liquid in the vacancy. (Credit: Tohoku Univ. NASA/JSC, SPring-8)

Figure 6: Crystals similar in shape to table corals found on the surface of the Ryugu sample (electron microscope image). The small, plate-like crystals are piled up to form the overall crystal. (Credit: Tohoku Univ.)

Figure 7: Paleomagnetic record remained in spherical magnetite (Fe₃O₄) crystals. (A) Transmission electron microscope image and (B, C) magnetic flux distribution images obtained by electron holography of magnetite cut from a Ryugu sample. Arrows and colors indicate the direction of magnetization. The concentric stripe pattern seen inside the particle indicates that the magnetic field wires wind in the direction of the arrow (called a spiral magnetic domain structure). Magnetic field wires seen on the outside of the particle are leakage fields from the particle, reflecting the magnetic field environment of Ryugu when the interior of the Ryugu parent body heated up and aqueous alteration reactions occurred. (Credit: Hokkaido Univ., Tohoku Univ.)

Explanation of words and phrases

1) Ca,Al-rich inclusions
The oldest solid particles in the solar system. It is thought to have been formed by condensation from high-temperature nebular gas near the sun during the formation of the solar system.

2) Ryugu parent body
Original asteroid Ryugu at the time of its birth. The diameter is thought to have been about 100 km. This parent body was destroyed to form the current Ryugu.

3) Primordial solar nebula, nebular gas
A disk of gas surrounding the sun that is thought to have existed in the solar system 4.5 billion years ago. It does not exist in the present solar system and is thought to have disappeared early in the formation of the solar system.

4) Muons
Negatively charged particles with a mass about 200 times that of an electron.

5) Asteroid family
Asteroid families are groups of asteroids with similar intrinsic orbital elements such as orbital radius, eccentricity, and inclination. Asteroids belonging to the same family are considered to be a debris group formed by collisional destruction of a common parent body.

6) Sugita et al, (2019) Science 364, eaaw0442. doi
10.1126/science.aaw0422/

7) Chondrules
spherical or near-spherical morphology particles that are abundant in meteorites of asteroidal origin. They are thought to have been formed by rapid cooling after heating to more than 1200℃ in the solar nebula.

Publication information

Journal Title	Science
DOI	10.1126/science.abn8671
Title of paper	Formation and evolution of carbonaceous asteroid Ryugu: Direct evidence from returned samples
Authors	T. Nakamura¹, M. Matsumoto¹, K. Amano¹, Y. Enokido¹, M. E. Zolensky², T. Mikouchi³, H. Genda⁴, S. Tanaka^5,6, M. Y. Zolotov⁷, K. Kurosawa⁸, S. Wakita⁹, R. Hyodo⁵, H. Nagano¹⁰, D. Nakashima¹, Y. Takahashi^11,12, Y. Fujioka¹, M. Kikuiri¹, E. Kagawa¹, M. Matsuoka^13,14, A. J. Brearley¹⁵, A. Tsuchiyama^16,17,18, M. Uesugi¹⁹, J. Matsuno¹⁶, Y. Kimura²⁰, M. Sato¹¹, R. E. Milliken²¹, E. Tatsumi^22,11, S. Sugita^11,8, T. Hiroi²¹, K. Kitazato²³, D. Brownlee²⁴, D. J. Joswiak²⁴, M. Takahashi¹, K. Ninomiya²⁵, T. Takahashi^26,27, T. Osawa²⁸, K. Terada²⁹, F. E. Brenker³⁰, B. J. Tkalcec³⁰, L. Vincze³¹, R. Brunetto³², A. Aléon-Toppani³², Q. H. S. Chan³³, M. Roskosz³⁴, J.-C. Viennet³⁴, P. Beck³⁵, E. E. Alp³⁶, T. Michikami³⁷, Y. Nagaashi^38,1, T. Tsuji^39,40, Y. Ino^41,5, J. Martinez², J. Han⁴², A. Dolocan⁴³, R. J. Bodnar⁴⁴, M. Tanaka⁴⁵, H. Yoshida¹¹, K. Sugiyama⁴⁶, A. J. King⁴⁷, K. Fukushi⁴⁸, H. Suga⁴⁹, S. Yamashita^50,51, T. Kawai¹¹, K. Inoue⁴⁸, A. Nakato⁵, T. Noguchi^52,53, F. Vilas⁵⁴, A. R. Hendrix⁵⁴, C. Jaramillo-Correa⁵⁵, D. L. Domingue⁵⁴, G. Dominguez⁵⁶, Z. Gainsforth⁵⁷, C. Engrand⁵⁸, J. Duprat³⁴, S. S. Russell⁴⁷, E. Bonato⁵⁹, C. Ma⁶⁰, T. Kawamoto⁶¹, T. Wada¹, S. Watanabe^5,26, R. Endo⁶², S. Enju⁶³, L. Riu⁶⁴, S. Rubino³², P. Tack³¹, S. Takeshita⁶⁵, Y. Takeichi^50,51,66, A. Takeuchi¹⁹, A. Takigawa¹¹, D. Takir², T. Tanigaki⁶⁷, A. Taniguchi⁶⁸, K. Tsukamoto¹, T. Yagi⁶⁹, S. Yamada⁷⁰, K. Yamamoto⁷¹, Y. Yamashita⁶⁹, M. Yasutake¹⁹, K. Uesugi¹⁹, I. Umegaki^72,65, I. Chiu²⁵, T. Ishizaki⁵, S. Okumura⁵², E. Palomba⁷³, C. Pilorget^32,74, S. M. Potin^13,75, A. Alasli¹⁰, S. Anada⁷¹, Y. Araki⁷⁶, N. Sakatani^70,5, C. Schultz²¹, O. Sekizawa⁴⁹, S. D. Sitzman⁷⁷, K. Sugiura⁴, M. Sun^17,18,78, E. Dartois⁷⁹, E. De Pauw³¹, Z. Dionnet³², Z. Djouadi³², G. Falkenberg⁸⁰, R. Fujita¹⁰, T. Fukuma⁸¹, I. R. Gearba⁴³, K. Hagiya⁸², M. Y. Hu³⁶, T. Kato⁷¹, T. Kawamura⁸³, M. Kimura^50,51, M. K. Kubo⁸⁴, F. Langenhorst⁸⁵, C. Lantz³², B. Lavina⁸⁶, M. Lindner³⁰, J. Zhao³⁶, B. Vekemans³¹, D. Baklouti³², B. Bazi³¹, F. Borondics⁸⁷, S. Nagasawa^{26, 27}, G. Nishiyama¹¹, K. Nitta⁴⁹, J. Mathurin⁸⁸, T. Matsumoto⁵², I. Mitsukawa⁵², H. Miura⁸⁹, A. Miyake⁵², Y. Miyake⁶⁵, H. Yurimoto⁹⁰, R. Okazaki⁹¹, H. Yabuta⁹², H. Naraoka⁹¹, K. Sakamoto⁵, S. Tachibana^11,5, H. C. Connolly Jr.⁹³, D. S. Lauretta⁹⁴, M. Yoshitake⁵, M. Yoshikawa^5,6, K. Yoshikawa⁹⁵, K. Yoshihara⁵, Y. Yokota⁵, K. Yogata⁵, H. Yano^5,6, Y. Yamamoto^5,6, D. Yamamoto⁵, M. Yamada⁸, T. Yamada⁵, T. Yada⁵, K. Wada⁸, T. Usui^5,11, R. Tsukizaki⁵, F. Terui⁹⁶, H. Takeuchi^5,6, Y. Takei⁵, A. Iwamae⁹⁷, H. Soejima^5,97, K. Shirai⁵, Y. Shimaki⁵, H. Senshu⁸, H. Sawada⁵, T. Saiki⁵, M. Ozaki^5,6, G. Ono⁹⁵ T. Okada^5,98, N. Ogawa⁵, K. Ogawa⁵, R. Noguchi⁹⁹, H. Noda¹⁰⁰, M. Nishimura⁵, N. Namiki^100,6, S. Nakazawa⁵, T. Morota¹¹, A. Miyazaki⁵, A. Miura⁵, Y. Mimasu⁵, K. Matsumoto^100,6, K. Kumagai^5,97, T. Kouyama¹⁰¹, S. Kikuchi^8,100, K. Kawahara⁵, S. Kameda^70,5, T. Iwata^5,6, Y. Ishihara¹⁰², M. Ishiguro¹⁰³, H. Ikeda⁹⁵, S. Hosoda⁵, R. Honda^104,105, C. Honda²³, Y. Hitomi^5,97, N. Hirata³⁸, N. Hirata²³, T. Hayashi⁵, M. Hayakawa⁵, K. Hatakeda^5,97, S. Furuya¹¹, R. Fukai⁵, A. Fujii⁵, Y. Cho¹¹, M. Arakawa³⁸, M. Abe^5,6, S. Watanabe¹⁰⁶, Y. Tsuda⁵.
Affiliations	¹Department of Earth Sciences, Tohoku University, Sendai 980-8578, Japan. ²NASA Johnson Space Center; Houston TX 77058, USA. ³The University Museum, The University of Tokyo, Tokyo 113-0033, Japan. ⁴Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo 152-8550, Japan. ⁵Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA), Sagamihara 252-5210, Japan. ⁶Department of Space and Astronautical Science, The Graduate University for Advanced Studies (SOKENDAI), Hayama 240-0193, Japan. ⁷School of Earth and Space Exploration, Arizona State University, Tempe AZ 85287, USA. ⁸Planetary Exploration Research Center, Chiba Institute of Technology, Narashino 275-0016, Japan. ⁹Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge MA 02139, USA. ¹⁰Department of Mechanical Systems Engineering, Nagoya University, Nagoya 464-8603, Japan. ¹¹Department of Earth and Planetary Science, The University of Tokyo, Tokyo 113-0033, Japan. ¹²Isotope Science Center, The University of Tokyo, Tokyo 113-0032, Japan. ¹³Laboratoire d'Etudes Spatiales et d'Instrumentation en Astrophysique (LESIA), Observatoire de Paris, Meudon 92195 France. ¹⁴Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, 305-8567, Japan. ¹⁵Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque NM 87131, USA. ¹⁶Research Organization of Science and Technology, Ritsumeikan University, Kusatsu 525-8577, Japan. ¹⁷Chinese Academy of Sciences (CAS) Key Laboratory of Mineralogy and Metallogeny, Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, CAS, Guangzhou 510640, China. ¹⁸CAS Center for Excellence in Deep Earth Science, Guangzhou 510640, China. ¹⁹Scattering and Imaging Division, Japan Synchrotron Radiation Research Institute, Sayo 679-5198, Japan. ²⁰Institute of Low Temperature Science, Hokkaido University,Sapporo 060-0819, Japan. ²¹Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI 02912, USA. ²²Instituto de Astrofísica de Canarias, University of La Laguna, Tenerife 38205, Spain. ²³Aizu Research Center for Space Informatics, The University of Aizu, Aizu-Wakamatsu 965-8580, Japan. ²⁴Department of Astronomy, University of Washington, Seattle WA 98195 USA. ²⁵Institute for Radiation Sciences, Osaka University, Toyonaka 560-0043, Japan. ²⁶Kavli Institute for the Physics and Mathematics of the Universe (The World Premier International Research Center Initiative), The University of Tokyo, Kashiwa 277-8583, Japan. ²⁷Department of Physics, The University of Tokyo, Tokyo 113-0033, Japan. ²⁸Materials Sciences Research Center, Japan Atomic Energy Agency, Tokai 319-1195, Japan. ²⁹Department of Earth and Space Science, Osaka University; Toyonaka 560-0043, Japan. ³⁰Institute of Geoscience, Goethe University, Frankfurt, 60438 Frankfurt am Main, Germany. ³¹Department of Chemistry, Ghent University, Krijgslaan 281 S12, Ghent, Belgium. ³²Institut d'Astrophysique Spatiale, Université Paris-Saclay, Orsay 91405, France. ³³Department of Earth Sciences, Royal Holloway University of London, Egham TW20 0EX, UK. ³⁴Institut de Minéralogie, Physique des Matériaux et Cosmochimie, Muséum National d'Histoire Naturelle, Centre national de la recherche scientifique (CNRS), Sorbonne Université, Paris, France. ³⁵Institut de Planétologie et d'Astrophysique de Grenoble, CNRS, Université Grenoble Alpes, 38000 Grenoble, France. ³⁶Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA. ³⁷Faculty of Engineering, Kindai University, Higashi-Hiroshima 739-2116, Japan. ³⁸Department of Planetology, Kobe University, Kobe 657-8501, Japan. ³⁹Department of Earth Resources Engineering, Kyushu University, Fukuoka 819-0395, Japan. ⁴⁰School of Engineering, The University of Tokyo, Tokyo 113-0033, Japan. ⁴¹Department of Physics, Kwansei Gakuin University, Sanda 669-1330, Japan. ⁴²Department of Earth and Atmospheric Sciences, University of Houston, Houston TX 77204, USA. ⁴³Texas Materials Institute, The University of Texas at Austin, Austin TX 78712, USA. ⁴⁴Department of Geoscience, Virginia Tech., Blacksburg VA 24061, USA. ⁴⁵Materials Analysis Station, National Institute for Materials Science, Tsukuba 305-0047, Japan. ⁴⁶Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan. ⁴⁷Department of Earth Science, Natural History Museum, London SW7 5BD, UK. ⁴⁸Institute of Nature and Environmental Technology, Kanazawa University, Kanazawa 920-1192, Japan. ⁴⁹Spectroscopy Division, Japan Synchrotron Radiation Research Institute, Sayo 679-5198, Japan. ⁵⁰Department of Materials Structure Science, The Graduate University for Advanced Studies (SOKENDAI), Tsukuba, Ibaraki 305-0801, Japan. ⁵¹Institute of Materials Structure Science, High-Energy Accelerator Research Organization, Tsukuba 305-0801, Japan. ⁵²Division of Earth and Planetary Sciences, Kyoto University; Kyoto 606-8502, Japan. ⁵³Faculty of Arts and Science, Kyushu University, Fukuoka 819-0395, Japan. ⁵⁴Planetary Science Institute, Tucson AZ 85719, USA. ⁵⁵The Pennsylvania State University, University Park, PA 16802, USA. ⁵⁶Department of Physics, California State University, San Marcos, CA 92096, USA. ⁵⁷Space Sciences Laboratory, University of California, Berkeley, California 94720, USA. ⁵⁸Laboratoire de Physique des 2 Infinis Irène Joliot-Curie, Université Paris-Saclay, CNRS, 91405 Orsay, France. ⁵⁹Institute for Planetary Research, Deutsches Zentrum für Luftund Raumfahrt, Rutherfordstraße 2 12489 Berlin, Germany. ⁶⁰Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena CA 91125, USA. ⁶¹Department of Geosciences, Shizuoka University, Shizuoka 422-8529, Japan. ⁶²Department of Materials Science and Engineering, Tokyo Institute of Technology, Tokyo 152-8550, Japan. ⁶³Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577, Japan. ⁶⁴European Space Astronomy Centre, 28692 Villanueva de la Cañada, Spain. ⁶⁵High Energy Accelerator Research Organization, Tokai 319-1106, Japan. ⁶⁶Department of Applied Physics, Osaka University, Suita, 565-0871, Japan. ⁶⁷Hitachi, Ltd., Hatoyama 350-0395, Japan. ⁶⁸Institute for Integrated Radiation and Nuclear Science, Kyoto University, Kumatori 590-0494, Japan. ⁶⁹National Metrology Institute of Japan, AIST, Tsukuba 305-8565, Japan. ⁷⁰Department of Physics, Rikkyo University, Tokyo 171-8501, Japan. ⁷¹Japan Fine Ceramics Center, Nagoya 456-8587, Japan. ⁷²Toyota Central Research and Development Laboratories, Inc., Nagakute 480-1192, Japan. ⁷³Istituto di Astrofisica e Planetologia Spaziali, Istituto Nazionale di Astrofisica, Rome 00133, Italy. ⁷⁴Institut Universitaire de France, Paris, France. ⁷⁵Faculty of Aerospace Engineering, Delft University of Technology, Delft, The Netherlands. ⁷⁶Department of Physical Sciences, Ritsumeikan University, Shiga 525-0058, Japan. ⁷⁷Physical Sciences Laboratory, The Aerospace Corporation, California 90245, USA. ⁷⁸University of Chinese Academy of Sciences, Beijing 100049, China. ⁷⁹Institut des Sciences Moléculaires d'Orsay, Université Paris-Saclay, CNRS, 91405 Orsay, France. ⁸⁰Deutsches Elektronen-Synchrotron Photon Science, 22603 Hamburg, Germany. ⁸¹Nano Life Science Institute (The World Premier International Research Center Initiative), Kanazawa University, 920-1192, Japan. ⁸²Graduate School of Life Science, University of Hyogo, Hyogo 678-1297, Japan. ⁸³Institut de Physique du Globe de Paris, Université de Paris, Paris 75205, France. ⁸⁴Division of Natural Sciences, International Christian University, Mitaka 181-8585, Japan. ⁸⁵Institute of Geosciences, Friedrich-Schiller-Universität Jena, 07745 Jena, Germany. ⁸⁶Center for Advanced Radiation Sources, The University of Chicago, Chicago, IL 60637, USA. ⁸⁷Optimized Light Source of Intermediate Energy to LURE (SOLEIL) Synchrotron, L'Orme des Merisiers, Gif sur Yvette Cedex, F-91192, France. ⁸⁸Institut Chimie Physique, Université Paris-Saclay, CNRS, 91405 Orsay, France. ⁸⁹Graduate School of Science, Nagoya City University, Nagoya 467-8501, Japan. ⁹⁰Department of Natural History Sciences, Hokkaido University, Sapporo 060-0810, Japan. ⁹¹Department of Earth and Planetary Sciences, Kyushu University, Fukuoka 819-0395, Japan. ⁹²Graduate School of Advanced Science and Engineering, Hiroshima University, Higashi-Hiroshima 739-8526, Japan. ⁹³Department of Geology, Rowan University, Glassboro NJ 08028, USA. ⁹4Lunar and Planetary Laboratory, University of Arizona; Tucson AZ 85721, USA. ⁹⁵Research and Development Directorate, JAXA, Sagamihara 252-5210, Japan. ⁹⁶Department of Mechanical Engineering, Kanagawa Institute of Technology, Atsugi 243-0292, Japan. ⁹⁷Marine Works Japan Ltd., Yokosuka 237-0063 Japan. ⁹⁸Department of Chemistry, The University of Tokyo, Tokyo 113-0033, Japan. ⁹⁹Faculty of Science, Niigata University, Niigata 950-2181, Japan. ¹⁰⁰National Astronomical Observatory of Japan, Mitaka 181-8588, Japan. ¹⁰¹Digital Architecture Research Center, National Institute of Advanced Industrial Science and Technology, Tokyo 135-0064, Japan. ¹⁰²JAXA Space Exploration Center, JAXA, Sagamihara 252-5210, Japan. ¹⁰³Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea. ¹⁰⁴Department of Information Science, Kochi University, Kochi 780-8520, Japan. ¹⁰⁵Center for Data Science, Ehime University, Matsuyama 790-8577, Japan. ¹⁰⁶Department of Earth and Environmental Sciences, Nagoya University, Nagoya 464-8601, Japan.

Press Release

Asteroid Explorer Hayabusa2 Initial Analysis Stone Team reveals Formation andevolution of the carbonaceous asteroid Ryugu.