A drawing of space near Jupiter, showing a portion of the radiation belts (in red), the Io torus (green) and the Europa torus (blue). The blue and green belts come from the atmospheres of the moons Europa and Io. The picture comes from measurements taken by the Cassini spacecraft.
The Atmosphere of Europa
The Galileo mission
discovered an amazing thing! Europa has its own atmosphere, although it is very, very thin. When fast moving molecules traveling through space near Jupiter hit Europa's atmosphere, they can bump molecules out of the atmosphere or off it's surface and make them get trapped in a donut-shaped belt called a "torus" around Jupiter.
Even though Ganymede
also have thin atmospheres, they do not seem to produce torii near Jupiter. Scientists think this has something to do with the shape of Jupiter's magnetic field
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