From the Cassini mission press release
“The footprint discovery at Saturn is one of the most important fields and particle revelations from Cassini and ultimately may help us understand Saturn’s strange magnetic field,” said Marcia Burton, a Cassini fields and particles scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “It gives us the first visual connection between Saturn and one of its moons.”
The auroral footprint measures approximately 1,200 kilometers (750 miles) by less than 400 kilometers (250 miles), covering an area comparable to California or Sweden. At its brightest, the footprint shone with an ultraviolet light intensity far less than Saturn’s polar auroral rings, but comparable to the faintest aurora visible at Earth without a telescope in the visible light spectrum. Scientists have not found a matching footprint at the southern end of the magnetic field line.
Jupiter’s active moon Io creates glowing footprints near Jupiter’s north and south poles, so scientists suspected there was an analogous electrical connection between Saturn and Enceladus. It is the only known active moon in the Saturn system with jets spraying water vapor and organic particles into space. For years, scientists used space telescopes to search Saturn’s poles for footprints, but they found none.
“Cassini fields and particles instruments found particle beams aligned with Saturn’s magnetic field near Enceladus, and scientists started asking if we could see an expected ultraviolet spot at the end of the magnetic field line on Saturn,” said Wayne Pryor, a lead author of the Nature study released today, and Cassini co-investigator at Central Arizona College in Coolidge, Ariz. “We were delighted to find the glow close to the ‘bulls-eye’ at the center of our target.”
Here’s a short video showing three observations of Enceladus’ ‘footprint’ on Saturn. Credit: NASA/JPL/University of Colorado/Central Arizona College.
And a video demonstrating “the hiss-like radio noise generated by electrons moving along magnetic field lines from the Saturnian moon Enceladus to a glowing patch of ultraviolet light on Saturn.” Credit: NASA/JPL/University of Iowa.
Finally, an animated graphic showing how Saturn and its moon Enceladus are electrically linked. Credit: NASA/JPL/University of Iowa.
There’s also an artist’s concept image, used as a featured image for this post. Credit: NASA/JPL/JHUAPL/University of Colorado/Central Arizona College/SSI.