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An Io volcano from above.
Voyager snapped an image of a ring around Jupiter.
The lines that cross Jupiter's moon Europa were first seen by earlier space probes, but showed that Europa's features were so flat, they "might have been painted on with a felt marker," according to a scientist. It is believed that the planet's surface may be covered by a water ice crust of up to three miles — hiding oceans as deep as 30 miles.