Bright scars on a darker surface testify to a long history of impacts on Jupiter's moon Callisto in this image of Callisto from NASA's Galileo spacecraft. This is the only complete global colour image of Callisto obtained by Galileo, which began orbiting Jupiter in 1995. Of Jupiter's four largest moons, Callisto orbits farthest from the giant planet. Callisto's surface is uniformly cratered but is not uniform in colour or brightness. Scientists believe the brighter areas are mainly ice and the darker areas are highly eroded, ice-poor material.
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