This image of Jupiter's aurora was captured by the Hubble Space Telescope on November 26, 1998. This ultraviolet view of the auroral oval is centered on Jupiter's magnetic north pole. Charged particles, moving at high speeds along Jupiter's magnetic field lines, collide with gases in the planet's atmosphere. Energy from the collisions generates the auroral lights. Since some of Jupiter's moons orbit inside its magnetosphere, the moons alter particle flows along the planet's magnetic field lines. This creates "footprints" or tracks of those moons in the aurora, three of which are visible in this image. The footprint of Io appears as a bright dot and "tail" along the far left edge of this view; the dimmer dots of the footprints of Ganymede and Europa (to the right of and beneath Ganymede's) are towards the bottom center of the image.
Image courtesy NASA, ESA, the Hubble Heritage Team (STScI/AURA), and John Clarke (University of Michigan).