Ion-kinetic modeling of Mercury’s magnetosphere: A reference for BepiColombo’s sixth flyby

The BepiColombo mission provides a unique opportunity to study Mercury’s magnetosphere, exosphere, and their interactions with the solar wind. The sixth Mercury flyby (MSB6) on January 8, 2025, offers a high-latitude trajectory potentially crossing through the plasma sheet and other key magnetospheric regions, making it a critical target for investigation. The aim of this study is to provide a model-based reference for ion and magnetic field measurements during MSB6 and to explore how solar wind and interplanetary magnetic field (IMF) conditions affect ion dynamics along the spacecraft trajectory. These results serve as a framework for interpreting BepiColombo’s observations, offering valuable insights that support the mission's scientific objectives. The global 3D hybrid plasma code AIKEF is employed to model Mercury’s magnetosphere under twelve scenarios, varying solar wind and IMF conditions. The model incorporates a kinetic treatment of ions and a self-consistent sodium exosphere. Ion differential energy spectra are computed for solar wind-origined protons and exopsheric sodium ions. Modeled ion and magnetic field data are discussed along the MSB6 trajectory. The results show significant variations in magnetospheric boundaries and particle populations depending on solar wind conditions. Bow shock crossings shift by up to 12 minutes across scenarios, while ion energies reach up to 10 keV for protons and 30 keV for sodium ions in the maximum solar wind case. Proton energy dispersion slopes in the plasma mantle are steeper under higher solar wind input. These findings provide critical insights into Mercury’s magnetospheric dynamics and form a foundation for interpreting BepiColombo’s upcoming observations.