The glowing patch of ultraviolet light near Saturn's north pole and the magnetic field lines were found by the ultraviolet imaging spectrograph and the fields and particles instruments on NASA's Cassini spacecraft, including the magnetospheric imaging instrument (MIMI).
The footprint shows the presence of an electrical circuit that connects Saturn with Enceladus, accelerating electrons and ions along the magnetic field lines.
The patch glows for the same reason as the planet's north and south polar auroras - energetic electrons diving into the planet's atmosphere - but isn't connected to the rings of auroras themselves.
The Cassini plasma spectrometer backed up the MIMI data, finding field-aligned electron beams in the area. A team of scientists analyzed the charged particle data and concluded that the electron beams had enough energy flux to generate detectable levels of auroral emission at Saturn.
They then passed target locations to Cassini's ultraviolet imaging spectrograph team, who found it in 2008.
The auroral footprint measures about 750 miles by 250 - about the size of California - and is located at about 65 degrees north latitude.
In the brightest image, it shines with an ultraviolet light intensity of about 1.6 kilorayleighs - far less than the Saturnian polar auroral rings, and about the same as the faintest aurora visible on Earth without a telescope in the visible light spectrum.
Scientists haven't yet found a matching footprint at the southern end of the magnetic field line.