In this Hubble telescope picture, a curtain of glowing gas is wrapped around Jupiter's north pole like a lasso. This curtain of light, called an aurora, is produced when high-energy electrons race along the planet's magnetic field and into the upper atmosphere where they excite atmospheric gases, causing them to glow.
The aurora resembles the same phenomenon that crowns Earth's polar regions. But this Hubble image, taken in ultraviolet light, also shows the glowing "footprints" of three of Jupiter's largest moons: Io, Ganymede, and Europa. Spanning the next two months in 2004, Jupiter's aurora will be scrutinized by two observatories: the Hubble telescope and the Cassini spacecraft, which will fly by the planet on its voyage to Saturn.
Image Credit: John Clarke (University of Michigan) and NASA