Auroral footprint of Ganymede

Abstract

The interaction of Ganymede with Jupiters fast rotating magnetospheric plasma gives rise to a current system producing an auroral footprint in Jupiters 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 Ganymedes orbital plane having a diameter of 8-20 RG. Temporal analysis of the auroral power of Ganymedes footprint reveals variations of different timescales: (1) a 5-hour timescale associated with the periodic flapping of Jupiters 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 Ganymedes magnetopause and/or to the recurrent presence of acceleration structures above Jupiters atmosphere. These three temporal components produce an auroral power emitted at Ganymedes footprint of the order of ∼0.2 to ∼1.5 GW. Copyright 2009 by the American Geophysical Union.