The is a ring-shaped cloud of and surrounding the planet Jupiter. Electrons collide with the ions, which absorb energy from the collisions and release it again as light. This process resembles the light emission by neon lights and the aurora borealis (northern lights).
Neon lights, however, get their power from the man-made electrical power grid. What powers the Io plasma torus?
Only part of the answer to this question is known.
The Io plasma torus is created by neutral atmospheric gases such as sulfur dioxide. These ions are created by the part of sunlight and bombardment by the of the plasma torus. These new ions and electrons are immediately accelerated to move with Jupiter's rotating magnetic field, and as a side effect the ions are heated to very high temperatures (tens of thousands of degrees), which is passed on to the electrons. Electrical currents are also driven by this acceleration process, forcing electrons to move at very high speeds. This energy leaves the system when the electrons excite the ions to give off this energy as ultraviolet light, which can be observed by telescopes (LINK to observations page)
Because these ions and electrons, or come from Io and its accompanying donut-shaped cloud of escaped atmospheric gases, this plasma cloud is also donut-shaped. Because of its shape, it is called the Io plasma torus. It rotates with Jupiter with a 10 hour period, while Io and its accompanying neutral gas ring requires 42 hours to revolve around Jupiter. Because Jupiter's magnetic field is tilted, the Io plasma torus rotation has a wobble or shimmy, like a car tire with a bent hub (see animation).