Resistive MHD simulations of Ganymede's magnetosphere 2. Birkeland currents and particle energetics

The Birkeland current flows generated by Ganymede's magnetospheric interaction with the Jovian magnetosphere are simulated by using a resistive MHD code. The total field-aligned current is estimated to be I_∥ ≈ 6.6 × 10 A. The power delivered to the Jovian auroral zone and to Ganymede's polar surface via energetic charged particle bombardment is about 6 × 10⁹W. Ions and electrons could gain as much as 2.9-48 keV at the reconnection site of the magnetopause. The production rate of oxygen and water molecules from the associated ion sputtering effect (Q_II ≈10²⁵ - 10²⁶ molecules/s, Q_I ≈ 1-4 × 10²⁶ molecules/s) can be derived from polar cap precipitation of the ambient Jovian energetic ions. Because Ganymede's Birkeland current system is highly time-variable in response to the Jovian magnetic field variations, the "footpoints" of the accelerated ion beams could have rapid changes and hence the motion of the hotspots of the oxygen airglow emission as observed by the Hubble Space Telescope.