We observe auroral emissions from both space and ground, and combine them with satellites and ground-based radar to promote a comprehensive understanding of auroral physics.
Certain types of auroras are of interest because of the very high energy precipitating electrons that affect the middle atmosphere. We launched the LAMP rocket in 2022, the first in the world to successfully observe these phenomena simultaneously. We also plan to launch the LAMP-2 rocket.
On the other hand, the high-latitude polar cap region, which is directly affected by the solar wind, is attracting attention from the perspective of space weather. We have developed 10 all-sky cameras and constructed an observation network that covers a wide area over the Antarctic Continent. Written by SAKANOI, Takeshi.

‘Geospace’ is the space around the Earth that consist of plasma (charged particles) originating from the Earth’s atmosphere and the solar wind. The electromagnetic waves propagating in the plasma are called ‘plasma waves’. In space, collisions between particles rarely occur, but the motion of particles is scattered by ‘collisions’ between plasma waves and charged particles. As a result, the enegetic particles precipiatte into the Earth’s atmosphere and cause polar auroras and affect the composition in the upper atmosphere. Therefore, studying the generation and propagation of plasma waves is important topic for understanding the connection between space and the Earth’s atmosphere. Using observations of plasma waves by the Arase satellite and groundbased aurora observations, we are investigating how plasma waves propagate through geospace and scatter enegetic charged particles, and studying the effects of space on the Earth’s atmosphere. Written by TSUCHIYA, Fuminori.

Have you heard that “Earth is like a giant magnet”? This magnet creates a vast region called the magnetosphere, which acts like a protective shield from the stream of charged particles known as the solar wind.

I study what’s going on inside this magnetosphere—especially what kinds of ions (electrically charged particles) are there, where they are, and how many of them exist by analyzing ElectroMagnetic Ion Cyclotron (EMIC) waves which are excited by ions traveling through the magnetosphere. Right now, I’m working with data from JAXA’s Arase satellite to try to uncover the types and ratios of ions present in the magnetosphere.

This research is expected to be applied to other planets. For example, BepiColombo is scheduled to arrive at Mercury in 2026, and JUICE will begin orbiting Jupiter in 2031. By applying this method, we hope to open new ways to explore particles and plasma environments surrounding planets. Written by KIKUCHI Riku.

Auroras glow above the Arctic and Antarctic. Far above them, powerful radio emissions known as Auroral Kilometric Radiation (AKR) are emitted into space at frequencies corresponding to the medium wave band. The intensity and frequency of this radiation are closely linked to various phenomena and structures within Earth’s magnetosphere that drive auroral activity. It also serves as an indicator showing the overall activity level in real time.

The Japan-U.S. joint satellite Geotail continuously observed this radio activity for approximately 30 years, from its launch in 1992 until 2022. This marks the first time such high-quality observations have been made by a single satellite over such an extended period. It spans three solar activity cycles, providing invaluable data for studying the effects of solar activity on Earth. Through long-term statistical analysis of this unique data, we aim to deepen our understanding of the Earth’s magnetosphere by examining the occurrence characteristics and variability trends of AKR.

Such radio activity is observed across planets. We anticipate research developments for Mercury, where the joint Japanese-European BepiColombo orbiter will begin observations in 2026; Jupiter, where the European JUICE orbiter will start observations in 2031; Saturn, explored by the US Cassini probe in the 2000s-2010s; and the two icy giant planets, Uranus and Neptune, for which future exploration plans are under consideration. Written by YAMANAKA Haruto.

The JAXA Arase satellite, which traverses the Earth’s radiation belts, investigates plasma activity extending from the ionosphere to regions beyond geostationary orbit. One of its primary observation targets is electron density, derived from the frequency of a wave known as the Upper Hybrid Resonance (UHR) detected by electric field antennas. However, in regions where the electron density is low and the wave signal is weak, the measurement accuracy decreases. In space, a satellite becomes electrically charged through the balance between incoming ambient electrons and photoelectrons emitted by sunlight.

By analyzing variations in this spacecraft potential, together with direct electron particle measurements, we have examined more than eight years of data collected since Arase’s launch in 2017. Since electron inflow depends on both electron density and temperature, this method provides valuable insight into how these parameters vary from the ionosphere up to the magnetosphere. Furthermore, spacecraft potential serves as a foundation for measuring electric fields that accelerate electrons and ions to high energies in space.

This study not only contributes to improving the accuracy of space electric field measurements, but also supports observations of the BepiColombo mission, a joint Japan–Europe project that will begin orbiting Mercury at the end of 2026. Written by KAWAGATA Keiya.