Auroral footprint of Ganymede

The interaction of Ganymede with Jupiter's fast rotating magnetospheric plasma gives rise to a current system producing an auroral footprint in Jupiter's ionosphere, usually referred to as the Ganymede footprint. Based on an analysis of ultraviolet images obtained with the Hubble Space Telescope, we demonstrate that the auroral footprint surface matches a circular region in Ganymede's orbital plane having a diameter of 8-20 R-G. Temporal analysis of the auroral power of Ganymede's footprint reveals variations of different timescales: (1) a 5-hour timescale associated with the periodic flapping of Jupiter's plasma sheet over Ganymede, (2) a 10-40 minute timescale possibly associated with energetic magnetospheric events, such as plasma injections, and (3) a 100-s timescale corresponding to quasiperiodic fluctuations, which might relate to bursty reconnections on Ganymede's magnetopause and/or to the recurrent presence of acceleration structures above Jupiter's atmosphere. These three temporal components produce an auroral power emitted at Ganymede's footprint of the order of similar to 0.2 to similar to 1.5 GW.