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Physicists Observe Direct Evidence of Effective Wave Growth Theory in Space

For the first time ever, physicists have observed energy being transferred from resonant electrons to whistler-mode waves in space. This offers confirmation of the non-linear growth theory of waves, which had been previously predicted. This breakthrough could provide a greater understanding of both space plasma physics and space weather, which can have an effect on satellites.

A team from Nagoya University in Japan has observed, for the first time, the energy transferring from resonant electrons to whistler-mode waves in space. Their findings offer direct evidence of previously theorized efficient growth, as predicted by the non-linear growth theory of waves. This should improve our understanding of not only space plasmaPlasma is one of the four fundamental states of matter, along with solid, liquid, and gas. It is an ionized gas consisting of positive ions and free electrons. It was first described by chemist Irving Langmuir in the 1920s.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>plasma physics but also space weather, a phenomenon that affects satellites.

When people imagine outer space, they often envision it as a perfect vacuum. In fact, this impression is wrong because the vacuum is filled with charged particles. In the depths of space, the density of charged particles becomes so low that they rarely collide with each other. Instead of collisions, the forces related to the electric and magnetic fields filling space, control the motion of charged particles. This lack of collisions occurs throughout space, except for very near to celestial objects, such as stars, moons, or planets. In these cases, the charged particles are no longer traveling through the vacuum of space but instead through a medium where they can strike other particles.

Whistler-Mode Wave Magnetic Field Energy Transfer

Whistler-mode wave magnetic field (blue arrows with spiral) propagating along the magnetic field (purple) interacting with electrons (red) passing through it. Credit: University of Tokyo

Around the Earth, these charged-particle interactions generate waves, including electromagnetic whistler-mode waves, which scatter and accelerate some of the charged particles. When diffuse auroras appear around the poles of planets, observers are seeing the results of an interaction between waves and electrons. Since electromagnetic fields are so important in space weather, studying these interactions should help scientists predict variations in the intensity of highly energetic particles. This might help protect astronauts and satellites from the most severe effects of space weather.

A team comprising Designated Assistant Professor Naritoshi Kitamura and Professor Yoshizumi Miyoshi of the Institute for Space and Earth Science (ISEE) at Nagoya UniversityNagoya University, sometimes abbreviated as NU, is a Japanese national research university located in Chikusa-ku, Nagoya. It was the seventh Imperial University in Japan, one of the first five Designated National University and selected as a Top Type university of Top Global University Project by the Japanese government. It is one of the highest ranked higher education institutions in Japan.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Nagoya University, together with researchers from the University of Tokyo, Kyoto University, Tohoku University, Osaka University, and Japan Aerospace Exploration Agency (JAXAFormed in 2003, the Japan Aerospace Exploration Agency (JAXA) was born through the merger of three institutions, namely the Institute of Space and Astronautical Science (ISAS), the National Aerospace Laboratory of Japan (NAL) and the National Space Development Agency of Japan (NASDA). JAXA performs various activities related to aerospace, from basic research in the aerospace field to development and utilization and is responsible for research, technology development, and launch of satellites into orbit, and is involved in advanced missions such as asteroid exploration and possible human exploration of the Moon.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>JAXA), and several international collaborators, mainly used data obtained using low-energy electron spectrometers, called Fast Plasma Investigation-Dual Electron Spectrometers, on board NASAEstablished in 1958, the National Aeronautics and Space Administration (NASA) is an independent agency of the United States Federal Government that succeeded the National Advisory Committee for Aeronautics (NACA). It is responsible for the civilian space program, as well as aeronautics and aerospace research. Its vision is "To discover and expand knowledge for the benefit of humanity." Its core values are "safety, integrity, teamwork, excellence, and inclusion." NASA conducts research, develops technology and launches missions to explore and study Earth, the solar system, and the universe beyond. It also works to advance the state of knowledge in a wide range of scientific fields, including Earth and space science, planetary science, astrophysics, and heliophysics, and it collaborates with private companies and international partners to achieve its goals.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>NASA’s Magnetospheric Multiscale spacecraft. They analyzed interactions between electrons and whistler-mode waves, which were also measured by the spacecraft. By applying a method of using a wave particle interaction analyzer, they succeeded in directly detecting the ongoing energy transfer from resonant electrons to whistler-mode waves at the location of the spacecraft in space. From this, they derived the growth rate of the wave. The researchers published their results in Nature Communications<em>Nature Communications</em> is a peer-reviewed, open-access, multidisciplinary, scientific journal published by Nature Portfolio. It covers the natural sciences, including physics, biology, chemistry, medicine, and earth sciences. It began publishing in 2010 and has editorial offices in London, Berlin, New York City, and Shanghai. ” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Nature Communications.

The most important finding was that the observed results were consistent with the hypothesis that non-linear growth occurs in this interaction. “This is the first time anybody has directly observed the efficient growth of waves in space for the wave-particle interaction between electrons and whistler-mode waves,” explains Kitamura. “We expect that the results will contribute to research on various wave-particle interactions and to also improve our understanding of the progress of plasma physics research. As more specific phenomena, the results will contribute to our understanding of the acceleration of electrons to high energies in the radiation belt, which are sometimes called ‘killer electrons’ because they inflict damage on satellites, as well as the loss of high-energy electrons in the atmosphere, which form diffuse auroras.”

Reference: “Direct observations of energy transfer from resonant electrons to whistler-mode waves in magnetosheath of Earth” by N. Kitamura, T. Amano, Y. Omura, S. A. Boardsen, D. J. Gershman, Y. Miyoshi, M. Kitahara, Y. Katoh, H. Kojima, S. Nakamura, M. Shoji, Y. Saito, S. Yokota, B. L. Giles, W. R. Paterson, C. J. Pollock, A. C. Barrie, D. G. Skeberdis, S. Kreisler, O. Le Contel, C. T. Russell, R. J. Strangeway, P.-A. Lindqvist, R. E. Ergun, R. B. Torbert and J. L. Burch, 28 October 2022, Nature Communications.
DOI: 10.1038/s41467-022-33604-2

This work was supported by Grant-in-Aid for Scientific Research (17H06140, 18H03727, 21K13979) from Japan Society for the Promotion of Science.

Source: SciTechDaily