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

A research group led by Professor Tetsuya Yokoyama of the Department of Earth and Planetary Science, Faculty of Science, Tokyo Institute of Technology, Associate Professor Tsuyoshi Iizuka and Professor Shogo Tachibana of the Graduate School of Science, University of Tokyo, and Professor Hisayoshi Yurimoto of the Graduate School of Science, Hokkaido University has measured the isotopic composition of the Cb-type asteroid Ryugu, and found that intense water metamorphism and water circulation on Ryugu caused local heterogeneity in chromium isotopic composition, They found that local inhomogeneities in chromium isotopic compositions were caused by the intense water metamorphism and water circulation that occurred on Ryugu.

Initial analysis of Ryugu samples revealed that the chemical and mineral compositions of the Cb-type asteroid Ryugu are similar to those of Ivuna-type carbonaceous meteorites, but there is a slight discrepancy between Ryugu and Ivuna-type carbonaceous meteorites in terms of chromium nucleosynthesis origin isotopic anomalies, the cause of which has been awaited to be clarified. The research group has been waiting for the cause of the anomaly to be clarified.

The research group measured nucleosynthetic origin isotope anomalies of chromium (54Cr) and titanium (50Ti) in a total of five Ryugu samples. The results showed that the 54Cr isotopic anomaly varied significantly from higher to lower than the average value for Ivna-type meteorites. This variation is inversely correlated with that of chromium isotopes (53Cr) derived from radiolytic decay of manganese-53 (53Mn), a short-lived nuclide. The 54Cr isotopic anomaly in the combined Ryugu samples (7-24 mg) (about 90 mg) is consistent with the average value for Ivna-type carbonaceous meteorites. In the initial analysis of the Bennu samples brought back by OSIRIS-REx, it was found that it is desirable to analyze a certain amount of sample (>0.1 g) in order to avoid the influence of heterogeneity.

The results of this research were published online in Science Advances on November 9, 2023 Japan time.

For more information, please refer to the following

Graduate School of Science web: https://www.s.u-tokyo.ac.jp/ja/press/10087/
Publication URL: https://www.science.org/doi/10.1126/sciadv.adi7048

Joint Press Release
Kotaro Kono, Professor, Astronomy Education and Research Center)

An international research team led by Assistant Professor Takuma Izumi of the National Astronomical Observatory of Japan (NAOJ) has observed the Compass Galaxy in the nearby universe with the ALMA telescope at an extremely high resolution of about one light year, and succeeded in quantitatively measuring the gas flow and its structure on a spatial scale of only a few light years around a supermassive black hole in all phases: plasma, atomic and molecular. The result was the world’s first successful quantitative measurement of the gas flow and its structure in all phases of plasma, atoms, and molecules. As a result, the accretion flow toward the supermassive black hole was clearly observed, and it was also clarified that the accretion flow is caused by a physical mechanism called “gravitational instability”. Furthermore, it was found that the majority of the accretion flow is not used for the growth of the black hole, but is instead ejected as atomic or molecular gas from the vicinity of the black hole, and then returns to the gas disk to become accretion flow to the black hole again, as if a fountain-like gas cycle is taking place. This is an important achievement toward a comprehensive understanding of the growth mechanism of supermassive black holes.

These observation results were published in the American journal Science on November 3, 2023 as “Supermassive black hole feeding and feedback observed on sub-parsec scales” by Izumi et al. (DOI: 10.1126/science.adf0569).

Professor Kotaro Kono of the Center for Astronomy Education and Research is participating in this research.

For more information, please visit the website of NAOJ and NAOJ ALMA Project.

https://www.nao.ac.jp/news/science/2023/20231103-alma.html

Joint Press Release
Satoshi Kasahara (Associate Professor, Department of Earth and Planetary Science)

Professor Lynn Kistler, Professor Yoshizumi Miyoshi, and Project Associate Professor Tomoaki Hori of Nagoya University and their colleagues, Associate Professor Kazushi Asamura and Professor Iku Shinohara of the Japan Aerospace Exploration Agency, Associate Professor Satoshi Kasahara and Assistant Professor Kunihiro Keika of the University of Tokyo, and Associate Professor Shoichiro Yokota of Osaka University, and their colleagues in the United States discovered that the main cause of space storms is plasma originating from the Earth, rather than plasma originating from the Sun as previously thought.

Through international collaboration, the research team analyzed data from a total of four scientific satellites, including the Japanese Geospace Exploration Satellite Arase, NASA of the United States, and ESA of Europe. As a result, they succeeded for the first time in separating the composition of solar- and terrestrial-origin plasma in near-Earth space (geospace), and discovered that the plasma in the Earth’s magnetosphere changes from solar to terrestrial origin during space storms. They also identified that the Earth-origin hydrogen ions are initially dominant in the development of space storms, and that the Earth-origin oxygen ions later become the main cause of space storms.

This indicates that not only ions of solar origin, as previously thought, but also those of terrestrial origin influence the development of space storms. During space storms, the space environment around the Earth changes drastically, which can cause disturbances to satellites and strong electric currents on the ground, which can affect the power grid. This research indicates that an accurate understanding of the behavior of not only plasma from the sun but also from the earth is necessary to understand the changes in the space environment caused by space storms and to predict space storms, which will force a major change in the conventional understanding of space storms.

The research results were published in the British scientific journal Nature Communications on October 30, 2023, at 7:00 p.m. CST.

For more details, please refer to the following

Graduate School of Science web: https://www.s.u-tokyo.ac.jp/ja/press/10073/
Publication URL: https://www.nature.com/articles/s41467-023-41735-3