The BepiColombo mission, a collaborative effort between the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA), has finally reached Mercury after an eight-year journey through space. In early September, two of the spacecraft’s orbiters—the Mercury Planetary Orbiter and the Mercury Magnetospheric Orbiter—separated from the transfer module that had carried them across the solar system. These orbiters are set to begin their detailed study of Mercury in November, with plans to separate from each other in December to perform individual scientific investigations. During its long voyage, BepiColombo has already made six close approaches to Mercury. One of the most significant of these was its fourth flyby in September 2024, when the spacecraft came within just 165 kilometers (103 miles) of the planet's surface. At that time, a powerful solar eruption sent a stream of high-energy electrons and protons toward Mercury. A Finnish-built instrument called SIXS (Solar wind and Ionospheric X-ray Sensor), designed to detect particles and X-rays, recorded how these solar particles interacted with Mercury’s magnetic field and struck its surface. "This flyby was truly unique," said Emilia Kilpua, the principal investigator of SIXS and a professor of space physics at the University of Helsinki. "The spacecraft was closer to Mercury’s surface than it will be in its final orbit, and we were fortunate that a major solar eruption occurred at that precise moment." The data collected by SIXS revealed that during such solar events, a vast number of high-energy particles reach Mercury’s surface, which has no significant atmosphere to shield it. These particles dislodge atoms and molecules from the surface, creating X-ray radiation. This process offers valuable clues about Mercury’s surface composition and its geological evolution. Mercury’s magnetic field is much weaker than Earth’s, and its magnetosphere—the region around a planet that is influenced by its magnetic field—is much smaller. Rami Vainio, co-principal investigator of SIXS and a professor at the University of Turku, explained that studying these conditions on Mercury can help scientists understand how powerful solar storms might affect Earth’s magnetosphere and atmosphere. The data from SIXS will also be used in the Center of Excellence in Space Resilience, a research initiative running from 2026 to 2033, where Kilpua and Vainio’s teams are involved.