Geissler, P., McEwen, A., and Porco, C. (2001). "Cassini Imaging of Visible Aurorae on Io and Europa." American Astronomical Society, DPS meeting #33, #9.02.

During its passage through the Jovian system, Cassini captured several sequences of images showing Io, Europa and Ganymede while the moons were eclipsed by Jupiter. Io was the best studied of the satellites: more than 500 images were acquired by Cassini's Imaging Science Subsystem during 4 separate eclipses of Io from 12/29/2000 to 1/05/2001. One of these imaging sequences was mistimed and captured only the start of the eclipse on 12/31/2000. Observations of the first three eclipses were made using 5 colors, while the last eclipse was imaged using 15 different filter combinations from 235 nm to 1100 nm. These data have been assembled into time-lapse sequences or "movies" recording entire eclipses. Major results from the Io observations include the detection of emissions at previously unknown near-ultraviolet and near-infrared wavelengths, motion of the equatorial sulfur dioxide and oxygen glows in response to the changing orientation of the Jovian magnetic field, and evidence contradicting the notion of eclipse "dimming" interpreted from earlier Galileo images. Europa was observed during an eclipse on 1/10/2001 and could still be detected in clear filter images more than an hour after ingress. Moonlight reflected from Ganymede could account for much of the signal but the images show that Europa is brightest along its limb, suggesting auroral emissions. Ultraviolet oxygen emissions with similar morphology were reported from HST/STIS observations by McGrath et al., 2001. Neutral oxygen and/or sodium emissions of about 10 kR could explain the observed brightness of Europa at visible wavelengths.