Note: Callisto is the third largest satellite in the solar system and orbits beyond Jupiter's main radiation belts. It has the lowest density of the Galilean satellites (1.86 grams/cubic centimeter). Callisto has the oldest landscape (about 4 billion years old), and most heavily cratered surface of any object in the solar system. These changes however are long dead, as Callisto is the only body greater than 1000 km in diameter in the solar system that has shown no signs of undergoing any extensive resurfacing since impacts have molded its surface.
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