Japan Aerospace Exploration Agency

Tohoku University

High Energy Accelerator Research Organization

J-PARC Center

Japan Synchrotron Radiation Research Institute

Hokkaido University

Tohoku University

Kyoto University

Kyushu University

Hiroshima University

The University of Tokyo

Summary of Presentation

Ryuguu samples returned to Earth by the asteroid explorer Hayabusa2 on December 6, 2020, were initially described (Phase-1 curation) at the Institute for Space and Astronautical Science (ISAS), JAXA. A part of the sample was distributed to the "Hayabusa2 Initial Analysis Team" consisting of six sub-teams and two "Phase-2 Curation Organizations". The Phase-2 Curation Organizations will produce individual HAYABUSA2 Particle catalogs will be created based on the "comprehensive analysis" characteristic of each of the Phase-2 curation institutes, and at the same time, the potential value of the HAYABUSA2 particles will be clarified through measurement and analysis according to the characteristics of the particles.

Professor Tomoki Nakamura and his research group at Graduate School of Science, Tohoku University analyzed the samples of the asteroid Ryuguu recovered by the Hayabusa2 spacecraft (17 particles including the third largest sample recovered by the spacecraft (Figure 1)) using cosmochemical and physical methods at five synchrotron radiation facilities and muon facilities in Japan, the United States and Europe. The results were analyzed using cosmochemical and physical methods. As a result, the history of Ryuguu from its formation to its impact destruction (formation and location in the solar system, information on astronomical material materials, types of ice contained, chemical evolution through reactions with water on the surface and in the interior of the celestial body, effects of celestial collisions, etc.) were determined. It was also found that the Ryuguu sample contains a mixture of material near the surface of the parent body and material in the interior of the body prior to impact destruction. Furthermore, we measured the hardness, heat transfer, specific heat, and density of the Ryuguu sample, and used these measurements to numerically simulate the temperature change due to heating in the interior of the parent body after the formation of Ryuguu and the collisional destruction process to reproduce the formation evolution of Ryuguu on a computer.

Figure: Formation and evolution process of Ryuguu inferred from the analysis of Ryuguu samples. The temperature distribution and age of the object and the collisional destruction process were obtained by numerical simulation.

The Graduate School of Science, Graduate School of Engineering, and University Museum from The University of Tokyo participated in this research result. The following members from the Department of Science are participating in this project.

Shogo Tachibana	Professor, Department of Earth and Planetary Science, UTokyo Organization for Planetary and Space Science
Yoshio Takahashi	Professor, Department of Earth and Planetary Science
Akira Takikawa	Associate Professor, Department of Earth and Planetary Science
Masahiko Sato	Assistant Professor, Department of Earth and Planetary Science
Seiji Sugita	Professor, Department of Earth and Planetary Science
Tomokatsu Morota	Associate Professor, Department of Earth and Planetary Science
Yuichiro Osa	Assistant Professor, Department of Earth and Planetary Science
Manabu Nishiyama	Doctoral student, Department of Earth and Planetary Science
Takahiro Kawai	Doctoral student, Department of Earth and Planetary Science
Hideto Yoshida	Project Specialist, Department of Earth and Planetary Science
Shizumoe Furuya	Project Specialist, UTokyo Organization for Planetary and Space Science

For more information, please visit the website of the Japan Aerospace Exploration Agency.

Journals

Journal name	Science
Title of paper	Formation and evolution of carbonaceous asteroid Ryugu: Direct evidence from returned samples
DOI number	10.1126/science.abn8671