|image: NASA/ESA, John Clarke (University of Michigan)|
This is a spectacular NASA Hubble Space Telescope close-up view of an electric-blue aurora that is eerily glowing on the giant planet Jupiter. Auroras are curtains of light resulting from high-energy electrons racing along the planets magnetic field into the upper atmosphere. The electrons excite atmospheric gases, causing them to glow.
This image shows the main oval of the aurora, which is centered on the magnetic north pole, plus more diffuse emissions inside the polar cap. Though the aurora resembles the same phenomenon that crowns Earths polar regions, the Hubble image shows unique emissions from the magnetic "footprints" of three of Jupiters largest moons. (These points are reached by following Jupiters magnetic field from each moon down to the planet).
Auroral footprints can be seen in this image from Io (along the left hand limb), Ganymede (near the center), and Europa (just below and to the right of Ganymedes auroral footprint). These emissions, produced by electric currents generated by the moons, flow along Jupiters magnetic field, bouncing in and out of the upper atmosphere. They are unlike anything seen on Earth.
December 14, 2000 inaugurated an intensive two weeks of joint observation of Jupiters aurora by Hubble and the Cassini spacecraft. The team will develop computer models that predict how the aurora operates, and this will yield new insights into the effects of the solar wind on the magnetic fields of planets.