Joint Press Release
Shogo Tachibana, Professor, Department of Earth and Planetary Science, Space and Planetary Science Organization

Moe Matsuoka, a researcher at the National Institute of Advanced Industrial Science and Technology (AIST) and Toru Kouyama, a team leader, National Institute of Advanced Industrial Science and Technology, in collaboration with Prof. Tomoki Nakamura, Tohoku University; Kana Amano, Japan Society for the Promotion of Science Research Fellow, Tohoku University; Dr. Takahito Osawa, Research Director, Japan Atomic Energy Agency; Prof. Shogo Tachibana, University of Tokyo; Prof. Hiroshi Naraoka and Associate Prof. Takashi Okazaki, Kyushu University, etc. and other researchers, conducted a direct comparison between the data obtained by the asteroid probe Hayabusa2 from the sky over the surface of the asteroid Ryugu and the data obtained by measuring samples collected and brought back (sample return) from Ryugu without exposing them to the Earth’s atmosphere.

As a result, we found that while the observed data from Ryugu’s surface and the sample return data agree well, there is a clear difference in the absorption of hydroxy groups (-OH), which is the key to determine the presence of water. In order to clarify the cause of this difference, experiments and data analysis of primitive meteorites similar to Ryugu, which are rich in hydrous silicates, revealed that Ryugu’s surface (about 1/100 mm) has been altered (space weathering) by exposure to cosmic rays and dust, resulting in partial loss of water.

This research result, which was only possible through a combination of remote observation from the spacecraft and analysis of collected samples, is one of the landmark results that demonstrate the importance of sample return in planetary exploration. The details of the study were published in Communications Earth & Environment on September 27, 2023 (JST).

For more information, please refer to the following

Graduate School of Science web: https://www.s.u-tokyo.ac.jp/ja/press/10047/
Publication URL: https://www.nature.com/articles/s43247-023-00991-3