Joint Press Release
Shogo Tachibana (Professor, Department of Earth and Planetary Science, ISAS)

Reflection spectra of asteroid recovered samples and meteorites provide clues to identify the constituent materials of asteroids from observationally obtained reflection spectra of asteroids.

A research group led by graduate student Kana Amano (currently a visiting researcher) and Professor Tomoki Nakamura of the Department of Earth Sciences, Graduate School of Science, Tohoku University, researcher Moe Matsuoka of the National Institute of Advanced Industrial Science and Technology (AIST), and Professor Shogo Tachibana of the Department of Earth and Planetary Science, Institute of Space and Planetary Science, Graduate School of Science, the University of Tokyo, and their colleagues have been studying asteroid samples recovered by the asteroid probe Hayabusa2 from asteroid Ryugu sample recovered from the asteroid Ryugu by the asteroid explorer Hayabusa2, and measured the reflection spectrum of the sample by devising a way to prevent it from reacting with the Earth’s atmosphere. By comparing Ryugu samples, meteorites from the same type of asteroid as Ryugu, and experimentally heated meteorites, they showed that the reaction of the meteorites with water and oxygen in the Earth’s atmosphere changed their reflection spectra to be brighter than they were in space. Based on this achievement, it is expected that the accuracy of identifying the constituent materials of asteroids by observation will be improved by considering how the reflection spectra of meteorites can change due to their alteration on the ground.

This result was published in Science Advances, a journal published by the American Association for the Advancement of Science (AAAS), on December 7, 2023.

For more information, please refer to the following

Graduate School of Science web: https://www.s.u-tokyo.ac.jp/ja/press/10144/
Publication URL: https://www.science.org/doi/10.1126/sciadv.adi3789

Joint Press Release
Aki Takigawa (Associate Professor, Department of Earth and Planetary Science)
Shogo Tachibana (Professor, Department of Earth and Planetary Science, ISAS)

Icy bodies and comets born far from the sun contain large amounts of nitrogen compounds such as ammonium salts. Such nitrogen-containing solids are thought to be very important as material for life, but no evidence of their transport to the Earth’s orbital region has been found. In this study, we examined sand from Ryugu, an asteroid orbiting near Earth, using an electron microscope and discovered that the very surface of the sand is covered with nitrided iron (iron nitride: Fe4N). Iron nitride is found on the surface of a mineral composed of iron and oxygen atoms called magnetite. We hypothesized that the iron nitride was formed by a chemical reaction on the surface of the magnetite when a small meteorite containing a large amount of ammonia compounds from an icy body hit Ryugu. On the surface of the asteroid, oxygen is lost from the magnetite surface due to exposure to ionic winds (solar wind) from the sun, and metallic iron, which easily reacts with ammonia, forms on the very surface. This is assumed to have promoted the synthesis of iron nitride derived from ammonia on the surface of the magnetite. This micrometeorite may have come from an icy body in the distant solar system, and it is possible that a larger amount of nitrogen compounds than previously realized were transported to the solar system near Earth to provide the material for life.

This work was conducted by a group led by Dr. Toru Matsumoto, a specific assistant professor at the Hakubi Center, Kyoto University; Dr. Takaaki Noguchi, a professor at the Graduate School of Science; Dr. Ryo Miyake, an associate professor; Dr. Yohei Igami, an assistant professor; Dr. Mitsutaka Haruta, an associate professor at the Institute for Chemical Research; and international collaborators, and published online in the British international journal Nature Astronomy on November 30, 2023, in the It was published online in the British international journal Nature Astronomy on November 30, 2023.

Professor Shogo Tachibana and Associate Professor Aki Takigawa of the Department of Earth and Planetary Sciences participated in the research results.

For more information, please refer to the following

Graduate School of Science web: https://www.s.u-tokyo.ac.jp/ja/press/10130/
Publication URL: https://www.nature.com/articles/s41550-023-02137-z