Plasma environment of Mercury’s magnetosphere as seen by BepiColombo during its third flyby

On June 19^th 2023, BepiColombo performed its third (MFB3) gravity assist maneuvers at Mercury. During this flyby, the spacecraft approaching the planet from dusk-nightside toward dawn-dayside and traveling down to close distances ~ 235 km altitudes above the planet’s surface. 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 an overview of the plasma environment from the Mercury Ion Analyzer (MIA) and the Mercury Electron Analyzer (MEA); moreover we will present the first ion composition observations of the Mass Spectrum Analyzer (MSA). MIA, MSA and MEA are 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). During this flyby, MSA and MIA 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., Nature Communications, under review].