Dr. Kanako Seki is a Professor at the Research Center for Advanced Science and Technology (RCAST), The University of Tokyo (UTokyo). She earned her Ph.D. in Science from UTokyo in 2000 and has previously served as Associate Professor at STEL/ISEE, Nagoya University and Professor at the Department of Earth and Planetary Science of UTokyo. Her research focuses on space environment and planetary system science, particularly space weather and space climate phenomena affecting Earth, Mars, and beyond. Prof. Seki combines spacecraft observations with advanced numerical modeling to study planetary ion dynamics in various magnetospheres, atmospheric escape, and conditions for habitable planets. She has contributed to various space missions, including Geotail, Arase, BepiColombo, and MAVEN, and has received prestigious honors such as the AGU Fred L. Scarf Award, NASA Group Achievement Awards, and the COSPAR William Nordberg Medal. Her work advances understanding of planetary environments and supports future space exploration.
As space exploration expands, our understanding of the space environment surrounding planets has deepened dramatically through a combination of ground- and/or satellite-based observations with numerical simulations. This progress has enabled us to discuss space environments and atmospheric escape in a comparative planetary context. The space environment around a planet depends on various conditions such as the distance from the Sun, solar activities, planetary size, atmospheric composition, and intrinsic magnetic field. Planets within the solar system are constantly exposed to the solar wind. The interaction between the solar wind and planetary atmospheres and magnetic fields forms their own characteristic magnetospheres. This interaction is also closely linked to atmospheric escape from terrestrial planets, influencing whether the planets can retain the atmosphere essential for a habitable environment. Insights derived from the studies of our solar system have increasingly been applied to studies of conditions for habitable exoplanets.
For magnetized planets with strong intrinsic magnetic fields, such as Earth, a large magnetosphere is formed, preventing most of the solar wind from directly penetrating into the atmosphere. Consequently, atmospheric escape is confined to the polar regions where the magnetic field opens into interplanetary space. In contrast, for non-magnetized planets like Venus and Mars, which lack a global intrinsic magnetic field, the interplanetary magnetic field carried by the solar wind becomes draped around the planet. This forms a structure called an induced magnetosphere, which allows the solar wind to directly interact with the upper atmosphere, leading to efficient atmospheric escape. This lecture focuses on the atmospheric escape from terrestrial planets, with a particular emphasis on effects of solar activities. Topics covered include ion outflows from low-altitude ionosphere during geomagnetic storms on Earth, the dependence of ion escape on the intrinsic magnetic field strength, and the impact of solar flares on ion escape from non-magnetized planets.