Space Environment and Planetary System Science Laboratory (Seki Lab.)
Research Center for Advanced Science and Technology (RCAST)

Advancing the Frontier in Space: Unraveling Space Weather and the Essential Conditions for Habitable Terrestrial Planets

The vast space surrounding us is a dynamic plasma world where space radiation flies about and plasma particles interact with each other in complex ways via electromagnetic field variations. The field of Space Environment and Planetary System Science has developed rapidly since the dawn of the space age. In our laboratory, we combine scientific satellite observations with our own numerical simulations/models to study universal plasma processes in universe, space weather phenomena that are becoming indispensable to modern society, and the effects of atmospheric escape on habitability of terrestrial planets.

Research on space weather phenomena on Earth, Mars, and beyond

“Space weather” refers to variable conditions on the Sun, throughout space, and in the planetary environment that can influence the performance and reliability of space-borne and ground-based technological systems and endanger human life and health. Phenomena related to the space weather include auroras and space radiation (high-energy particles) variations. Around Earth, we are conducting research through close collaboration between satellite observations by the geospace exploration satellite “Arase,” ground-based observations, and numerical simulations. The approach of the integrated studies that combines diverse data tailored to the scientific challenges we aim to address. The space environment surrounding a planet varies significantly depending on whether the planet possesses a global intrinsic magnetic field. As the frontier of the human exploration expands from the Moon to Mars, extending current Earth-based research into planetary space weather has become an urgent necessity. We participate also in Mars exploration missions such as NASA’s MAVEN and JAXA’s MMX. We combine these observations with our own numerical models to advance our understanding of planetary space weather phenomena such as Martian aurorae.

Research on space climate to understand the impact of stellar activities on planetary environments

An atmosphere is essential for maintaining a habitable surface environment with oceans like Earth. Understanding atmospheric escape to space, which determines the conditions for atmospheric retention, is one of the key issues in elucidating the recipe for a second Earth. In particular, understanding how various proposed atmospheric escape mechanisms depend on stellar activity and planetary magnetic field strength is key to elucidating the diversity and universality of terrestrial exoplanets. To address this issue, we have developed original numerical models that have been tested by observations of planets in our solar system and are beginning to apply them to exoplanets. For example, our recent studies have revealed that intense solar activity at that time may have caused significant atmospheric escape from ancient Mars, leading to the loss of most of its atmosphere and habitable environment. Our research has also shown that the presence of an intrinsic magnetic field can suppress atmospheric escape from Venus-like exoplanets, significantly extending their atmospheric retention (habitable) period. Additionally, we are conducting research on how space radiation interacting with the atmosphere influences the formation of prebiotic molecules based on photochemical models.