Mercury has a tenuous atmosphere containing alkali metals. In particular, the neutral sodium emission is bright and suitable for ground-based observation.

We use Tohoku University’s 60 cm telescope (T60) in Hawaii to perform 2D observations of Mercury’s exosphere.

In coordination with the BepiColombo spacecraft, which will enter Mercury’s orbit in 2027, we aim to observe Mercury both from the ground and in situ. Mercury’s magnetosphere is much smaller than Earth’s and varies on a timescale of just a few minutes.

By observing these rapid variations, we hope to better understand the interaction between Mercury’s atmosphere and its magnetic environment.

Venus is believed to have once possessed a substantial amount of water, but today it is an extremely dry planet.

One of the key processes behind this transformation is known as atmospheric escape — the loss of atmospheric particles into space.

This research aims to understand how the solar wind, a high-energy stream of charged particles emitted by the Sun, influences the hydrogen-rich upper atmosphere (exosphere) of Venus.

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.

‘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.

“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 lectromagnetic ion cyclotron (EMIC) waves. Right now, I’m working with data from the Arase satellite to try to uncover the types and ratios of ions present in the magnetosphere.

This could also help us study 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 planetary magnetic fields and plasma environments across the solar system.”

Auroral Kilometric Radiation (AKR), a type of auroral radio emission from Earth, is closely associated with various phenomena and structures in the Earth’s magnetosphere. It serves as a valuable barometer for understanding the state and dynamics of the magnetosphere.

However, long-term statistical studies of AKR—particularly those focusing on its correlation with solar activity—have been limited.

In this study, I aim to conduct a long-term statistical analysis of AKR using data from the Geotail satellite, which has observed the Earth’s magnetosphere for nearly 30 years.

By clarifying the occurrence characteristics and temporal variations of AKR, I hope to contribute to a deeper understanding of the Earth’s magnetospheric environment.

Since 2017 the Arase satellite has been investigating electron number density and temperature in the near-Earth environment. Electron density is derived from the upper-hybrid resonance (UHR) frequency recorded by the onboard electric-field antennas, yet this technique tends to underestimate density in low-density regions. To address the bias, we integrated satellite potential, in-situ particle measurements, and solar UV flux, and compared the resulting data set for 2017–2022. The analysis shows that, under geomagnetically quiet conditions, satellite potential and electron density exhibit a clear proportional relationship, with an additional dependence on electron temperature. These findings reduce measurement uncertainties and will enhance the accuracy of plasma observations by BepiColombo/MMO, scheduled to explore Mercury in 2026.

I analyze the Martian lower atmosphere conditions from OMEGA observation data, which is a near-infrared imaging spectrometer onboard the Mars Express. In collaboration with a French research team, I developed a system to estimate the dust optical depth, dust vertical distribution, and surface pressure on Mars. This contributes to understanding Martian meteorological phenomena. The system is also expected to be used in future Mars missions, including the upcoming MMX mission.

Jupiter possesses an exceptionally strong magnetic field, and within its magnetosphere lies a vast distribution of plasma released from its volcanically active moon, Io. This plasma forms a structure known as the Io plasma torus, from which narrowband kilometric radiation (nKOM) is emitted.
The objective of my research is to investigate the long-term variations in the occurrence frequency and intensity of nKOM emissions, in order to clarify their relationship with magnetospheric dynamics such as injection phenomena within Jupiter’s magnetosphere.

We focus on the volcanically active Io and the icy moon Europa. Sulfur and oxygen ions generated from Io spread to Europa’s orbit as a doughnut-shaped Io plasma torus. However, time and spatial continuity of plasma parameters at Europa’s orbit has rarely been investigated because of the limited observations. This study aims to estimate the electron density, electron temperature, and ion composition in Io plasma torus from Io’s orbit to Europa’s orbit using Hisaki satellite data. As a result, the sulfur and oxygen ion emission lines were successfully identified at Europa’s orbit. We will work on how the plasma density and ion composition at Europa’s orbit changed in response to Io’s volcanic activity occurred in late January 2015.

Jupiter’s polar regions exhibit auroral emissions with complex structures. The “footprint aurora” associated with Europa is a signature of the plasma environment around Europa. Using the observations of the footprint aurora made by the Hubble Space Telescope, I detected temporal variations in the plasma mass density and temperature around Europa. Currently, I am continuing my research using the high spatial resolution data obtained by the Juno spacecraft. A detailed investigation of the footprint aurora will lead to a deeper understanding of the plasma environment surrounding Europa.

Jupiter’s synchrotron radiation (JSR) is emitted from the high-energy electrons trapped in the Jupiter’s radiation belts. Its intensity and frequency depend on electron energy, electron number density, and magnetic field strength.

We are observing the JSR with several telescopes, including the Giant Metrewave Radio Telescope (GMRT) in India, and analyzing the data to estimate the spatial structure and energy spectrum of electrons in Jupiter’s radiation belts.

In this study, we focus on the refraction of planetary radio emissions as they pass through the ionospheres of moons—electrically charged layers of the atmosphere—and develop a method to derive electron densities from their bending behavior. Conventional observation techniques have limitations in spatial coverage. To address this, we propose a new approach that simulates the radio wave paths through the ionospheres using computer-based ray tracing and inversely estimates the electron density. We are currently applying this method to derive the electron density distribution of Titan’s ionosphere using data from the Cassini spacecraft. Furthermore, in preparation for the upcoming JUICE mission, we are investigating the use of radio wave polarization (i.e., rotational direction) to improve the accuracy of the analysis.