Electrodynamic coupling between Ganymede and the Jovian ionosphere

The electromagnetic coupling between Ganymede and the Jovian ionosphere manifests it effects all along the magnetic field lines convecting across Ganymede, down to Jupiter's upper atmosphere. As the Alfvén waves generated by the local interaction propagate along the magnetic field lines, they accelerate charged particles in both parallel and anti-parallel directions. Part of these particles, mostly electrons, impact the neutral atmosphere of the giant planet and create auroral emissions, called the Ganymede footprint. This auroral footprint takes the form of several luminous spots followed by an extended curtain of light emission: the Ganymede footprint tail. The electron precipitation also results in a loss cone pitch angle distribution, driving the cyclotron-maser instability that generates characteristic decametric radio emissions. The morphology and the relative motion of the auroral features, as well as the time variability and the energetics of the radio emissions, provide key elements to understand the physical mechanisms at play. Moreover, the location of the Ganymede footprint proved to be an essential reference point in order to magnetically map processes from the Jovian ionosphere to the magnetospheric equatorial plane and vice-versa. In this chapter, we explore how these long-range consequences of this electrodynamic coupling have been discovered and what they tell us about the underlying physics and the state of the magnetosphere.