Mercury’s magnetosphere: BepiColombo’s flybys observations of the ion composition from the Mass Spectrum Analyzer

International audienceOn June 23rd 2022 and 19th 2023, BepiColombo performed its second (MFB2) and third (MFB3) gravity assist maneuvers at Mercury. The two flybys had similar trajectories, the spacecraft approaching the planet from dusk-nightside toward dawn-dayside and traveling down to extremely close distances (down to ~198 km and ~ 235 km altitudes above the planet’s surface for MFB2 and MFB3, respectively). Even though BepiColombo is in a so-called “stacked configuration” during cruise (meaning that most of the instruments cannot be fully operated yet), a number of instruments can still make interesting observations. Particularly, despite their limited field-of-view, the particle sensors allow us to get a hint on the plasma composition and dynamics along a unique path across the magnetosphere and very close to the planet.In this presentation, we will show the first ion composition observations of the Mass Spectrum Analyzer (MSA) at Mercury during the two flybys. MSA is part of the Mercury Plasma Particle Experiment (MPPE, PI: Y. Saito) consortium that is a comprehensive instrumental suite for plasma, high-energy particle and energetic neutral atom measurements onboard Mio (Saito et al. 2021). MSA is a time-of-flight spectrometer that provides information on the plasma composition and the three-dimensional ion distribution functions in the ~ 10 eV/q-38 keV/q energy range and in the ~ 1-60 amu mass range (Delcourt et al. 2016). We will focus on the third Mercury flyby during which MSA revealed the presence of energetic (> 10 keV) and cold (< 100 eV) heavy ions inside the magnetosphere around closest approach. Moreover, we will show major features of the Mercury magnetosphere highlighting different regions: 1) plasma sheet, 2) nightside bounday-layer and 3) magnetosheath [Hadid et al., in prep]