Characterizing the Magnetic and Plasma Environment Upstream of Ganymede

Abstract

We present an application of the latest UCL-AGA magnetodisc model (MDISC) to the study of the magnetic and plasma conditions in the near-Ganymede space. By doing this, we provide a comparison with measurements from Juno's most recent flyby of the Jovian moon, perijove 34 (PJ34). We find good agreement between the model results and the magnetometer data, pointing toward a hot plasma index value $K_h=$ (2.719$\pm$0.024)$\times$10⁷ Pa m T⁻¹ and an effective magnetodisc radius $r_{\text{max}}=$ (79.5$\pm$1.1) Jupiter radii for the Jovian magnetosphere, for the duration of the trajectory, suggesting a configuration with middling levels of expansion. We also predict the plasma conditions observed by Juno during the same flight-path, as well as the typical conditions over the orbit of Ganymede, with the magnetic and hot plasma pressures assuming dominant roles. Finally, these results are compared with functional fits of a compilation of Galileo flyby data obtained in the vicinity of Ganymede's orbit, suggesting Juno experienced somewhat similar conditions, despite a systematic overestimation in magnetic field intensity in the near-Ganymede space.