2023-10-30 09:51:57
JAXA’s Mio satellite, one of the BepiColombo mission satellites, was launched in 2018 for the exploration of Mercury’s magnetosphere. Its insertion into final orbit around the planet is planned for December 2025. Unlike the Mariner 10 and MESSENGER satellites which had already explored Mercury, Mio is equipped with a set of instruments designed to study electromagnetic waves in Mercury’s environment and their role in the acceleration of charged particles. Before this date the satellites will have to fly over Earth, Venus and Mercury several times in order to carry out gravitational assistance maneuvers.
The study was carried out by a Franco-Japanese team including scientists from CNRS-INSU (see box), using data from induction magnetometers (DBSC and LF-SC) from Mio built jointly with Kanazawa University. Data acquired during flybys of Mercury (in 2021 and 2022) made it possible to detect the first electromagnetic waves (known as chorus) around the planet. This type of waves, whose frequencies are close to the frequency of gyration of electrons around the magnetic field, makes the interaction between the two (chorus waves and gyration waves of electrons) effective (resonance phenomenon), which allows to accelerate electrons more efficiently, hence their importance.
What surprised the researchers was the spatial location of these waves in an extremely limited region on the day side of the magnetosphere. This location appears to be strongly correlated with the curvature of the magnetic field lines due to the dynamic pressure of the solar wind. A theoretical and numerical study showed that in the day side energy is transferred more efficiently from electrons to electromagnetic fields, thus creating conditions favoring the generation of chorus waves.
This study should provide a better understanding of various Hermian energetic phenomena (aurora, precipitation of particles on the surface of the planet, etc.) and their impact on the large-scale dynamics of the magnetosphere. Further studies will be carried out from December 2025 once the instruments are deployed following the satellites are inserted into their final orbit around Mercury.
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