Ion observations and composition from MSA and MIA during BepiColombo's final gravity assist maneuver at Mercury

On January 8th, 2025, BepiColombo performed its sixth and final gravity assist maneuver (MFB6) at Mercury. This final maneuver followed the previous fourth flyby (MFB4), which was conducted in the polar regions. Unlike the first three flybys, which occurred near the equatorial regions, the spacecraft approached the planet from south to north, traveling from the nightside to the dayside across the cusp region at altitudes as low as ~265 km above the planet’s surface.

Although BepiColombo is in a "stacked configuration" during cruise (meaning that most of the instruments cannot be fully operated), several instruments remain capable of making valuable observations. In particular, despite their limited field of view, the particle sensors provide insights into the plasma composition and dynamics along a unique path across the magnetosphere, close to the planet. Notably, the Mass Spectrum Analyzer (MSA), part of the Mercury Plasma Particle Experiment (MPPE, PI: Y. Saito) consortium, detected clear evidence of Na+ ions and heavier ion species such as K+ around closest approach. In this presentation, we provide an overview of the ion observations from MSA and the Mercury Ion Analyzer (MIA), focusing on the ion composition during MFB6 in comparison with MFB4.