Mercury’s plasma environment after BepiColombo’s third flyby

Abstract

Understanding Mercury’s magnetosphere is crucial for advancing our comprehension of how the solar wind interacts with the planetary magnetospheres. Despite previous missions, several gaps remain in our knowledge of Mercury’s plasma environment. Here, we present findings from BepiColombo’s third flyby, offering a synoptic view of the large scale structure and composition of Mercury’s magnetosphere. The Mass Spectrum Analyzer (MSA), Mass Ion Analyzer (MIA), and Mass Electron Analyzer (MEA) on the magnetospheric orbiter reveal insights, including the identification of trapped energetic hydrogen (H+) with energies around 20 keV e−1 evidencing a ring current, and a cold ion plasma with energies below 50 eV e−1. Additionally, we observe a Low-Latitude Boundary Layer (LLBL), which is a region of turbulent plasma at the edge of the magnetosphere, characterized by bursty ion enhancements, indicating an ongoing injection process in the duskside magnetosphere flank. These observations during cruise phase provide a tantalizing glimpse of future discoveries expected from the Mercury Plasma Particle Experiment (MPPE) instruments after orbit insertion, promising broader impacts on our understanding of planetary magnetospheres. Due to its proximity to the Sun, the space plasma environment of Mercury is tightly coupled with the interior and the surface of the planet, and their interaction facilitate the escape of planetary material and energy exchange. The authors present data from the third flyby of the BepiColombo spacecraft revealing new evidence of trapped energetic hydrogen (H+) with energies of around 20 keV/e and highlight the presence of cold ion population below 50 eV/e in Mercury’s magnetosphere.