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