Whistler-mode waves in Mercury’s magnetosphere observed by BepiColombo/Mio

Whistler-mode chorus waves are natural electromagnetic emissions known to play a key role in electron acceleration and loss mechanisms via wave–particle interactions in planetary magnetospheres. Chorus waves have not yet been detected in Mercury’s magnetosphere due to the lack of suitable instruments in the probes that previously visited the planet as well as to its harsh environment. Here, we present the direct probing of chorus waves in the localized dawn sector during the first and second Mercury flybys by the BepiColombo/Mio spacecraft. Mio’s search coil magnetometers detected chorus events with tens of picotesla intensities in the dawn sector, while no clear chorus activity was observed in the night sector. The simulation results suggest that this regional difference could be due to the impact of background magnetic field inhomogeneities on the nonlinear wave generation process. This observational evidence is crucial for understanding the energetic electron dynamics of the localized dawn sector of Mercury’s magnetosphere.