BepiColombo 2nd Mercury flyby: Ion composition measurements from the Mass Spectrum Analyzer onboard Mio
Résumé
On June 23rd 2022, BepiColombo performed its second gravity assist maneuver (MFB2) at Mercury. Just like the first encounter that took place on October 1st 2021, the spacecraft approached the planet from dusk-nightside toward dawn-dayside, traveling down to an extremely close distance (at ~198 km altitude above the planet's surface). This distance is smaller than that of the two BepiColombo orbiters when they will orbit the planet after insertion in 2025. Even though BepiColombo is in a so-called "stacked configuration" during cruise (meaning that most of the instruments cannot be fully operated yet), the 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 very close to the planet. In this presentation, we will show the first observations of the Mass Spectrum Analyzer (MSA) at Mercury during MFB2. 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 ion composition (1) at the closest approach that occurred around 09:44 UT, and (2) during the outbound sequence in the foreshock region between ~10:00 UT and ~ 10:30 UT.