Morphology and time variability of Io's visible aurora

Clear-filter imaging of lo during the Galileo nominal and extended missions recorded diffuse auroral emissions in 16 distinct observations taken durin g 14 separate eclipses over a two year period. These images show that the m orphology and time variability of the visible aurora have several similarit ies to lo's far ultraviolet emissions. The orbital leading hemisphere of lo is consistently brighter than the trailing hemisphere, probably due to a g reater concentration of torus electrons in the wake region of the satellite . The locations of the polar limb glow and the bright equatorial glows appe ar to correlate with Io's System III longitude. Unlike the far ultraviolet emissions, the visible aurorae are enhanced near actively venting volcanic plumes, probably because of molecular emission by SO2.