An Overview of the Auroras of Jupiter and Saturn from the Cassini Perspective (Invited)

The Cassini spacecraft flew by Jupiter in late 2000 and early 2001 and has been orbiting Saturn since 2004. A highlight of the mission has been an unprecedented collection of high-resolution auroral images of Saturn obtained in the visible by Cassini ISS, in the infrared by Cassini VIMS, and in the ultraviolet by Cassini UVIS. We will briefly discuss auroral observations of Jupiter by Cassini showing auroral storms and episodes of periodic pulsations, then highlights from the large database of Saturn auroral images and movies, and complementary fields and particles data. Complementary and sometimes simultaneous HST images will also be shown.

Saturn's auroras exhibit a wide variety of changing forms. At times multiple narrow arcs are seen, at other times a single broader emission is seen. The polar cap inside the oval exhibits changing discrete forms, often near noon local time in the polar cusp region. Satellite footprints associated with Enceladus are very rarely seen. Bright auroral pulsations on the main oval sometimes occur, separated by about an hour. At times these seem associated with the moon Mimas, occurring at the sub-Mimas longitude and moving with the moon. We indicate a possible mechanism for this, involving Mimas control of the width of the Cassini Division, which forms a channel for plasma flow connecting Saturn's rings and/or flowing through Saturn's rings.