A Model of Ganymede's Magnetic and Plasma Environment During the Juno PJ34 Flyby.

Using a hybrid model (kinetic ions, fluid electrons), we provide context for plasma and magnetic field observations from Juno's PJ34 flyby of Ganymede on 07 June 2021. We consider five model configurations that successively increase the complexity of Ganymede's atmosphere and ionosphere by including additional particle species and ionization mechanisms. We examine the density and flow patterns of pick‐up ions with small H2+ $\left({\mathrm{H}}_{2}^{+}\right)$, intermediate (H2O+), and large O2+ $\left({\mathrm{O}}_{2}^{+}\right)$ masses in Ganymede's interaction region. The results are validated by comparing the modeled magnetic field and ion densities against time series from Juno's magnetometer and plasma instruments. Our major findings are: (a) Ganymede's internal dipole dominated the magnetic field signature observed inside the moon's magnetosphere, while plasma currents shaped the field perturbations within the "wake" region detected along the Jupiter‐averted magnetopause. (b) Ganymede's pick‐up tail leaves a subtle, but clearly discernible imprint in the magnetic field downstream of the moon. (c) Heavy pick‐up ions dominate ionospheric outflow and form a tail with steep outer boundaries. (d) During the flyby, the position of Ganymede's Jupiter‐facing magnetopause varied in time due to Kelvin‐Helmholtz waves traveling along the boundary layer. As such, the location of the Jupiter‐facing magnetopause observed by Juno represents only a single snapshot of this time‐dependent process. (e) Ionospheric hydrogen ions are partially generated outside of Ganymede's magnetopause, forming a dilute H2+ ${\mathrm{H}}_{2}^{+}$ corona that surrounds the moon's magnetosphere. (f) Most H2O+ ions are produced at low latitudes where field lines are closed, resulting in a very dilute pick‐up tail for this species. Key Points: Using a hybrid model, we provide three‐dimensional context for plasma and magnetic field observations from the Juno PJ34 flyby of GanymedeEscaping heavy ions from Ganymede's ionosphere cause subtle, but discernible modifications to the magnetic field in the vicinity of the moonGanymede's sub‐Jovian magnetopause is susceptible to Kelvin‐Helmholtz instabilities, causing the location of the boundary layer to oscillate [ABSTRACT FROM AUTHOR]