What it is
During BepiColombo's fourth flyby of Mercury on 4 September 2024, the spacecraft passed within just 165 km of the surface while fluxes of high-energy solar particles were elevated. Using the onboard Solar Intensity X-Ray and Particle Spectrometer (SIXS), the authors tracked how those particles penetrated Mercury's magnetosphere and found that the flux variations depended on particle type, direction, and energy. The disappearance of protons was linked to magnetic shadowing by the planet, while electron dropouts were attributed to a wide magnetic loss cone.
Why it matters
The close approach and coincident solar particle event gave a rare in-situ view of how a weakly magnetized rocky planet close to its star shields, or fails to shield, its surface from high-energy particles. The results show that sustained high-energy particle precipitation can reach the surface during such events, which the authors link to regolith alteration and exospheric variability with implications for surface geochemistry and potential habitability.
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Filed underPlanetary Science and Exploration, Astro and Planetary Science, Ionosphere and magnetosphere dynamics