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Heavily cratered surface of Callisto
This image shows the heavily cratered surface of Callisto. It was taken by Voyager 2 on July 7, 1979. An enormous impact basin with concentric rings is located near the top and slightly left of center.
Jupiter: Moons: Callisto

With a diameter of over 4,800 km (2,985 miles), Callisto is the third largest satellite in the solar system and is almost the size of Mercury. Callisto is the outermost of the Galilean satellites, and orbits beyonds Jupiter's main radiation belts. It has the lowest density of the Galilean satellites (1.86 grams/cubic centimeter). Its interior is probably similar to Ganymede except the inner rocky core is smaller, and this core is surrounded by a large icy mantle. Callisto's surface is the darkest of the Galileans, but it is twice as bright as our own Moon.

Callisto is the most heavily cratered object in the solar system. It is thought to be a long dead world, with a nearly complete absence of any geologic activity on its surface. In fact, 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. With a surface age of about 4 billion years, Callisto has the oldest landscape in the solar system.
Just the Facts
Distance from Jupiter: 
1,883,000 km
Equatorial Radius: 
2,403 km
107,593,000,000,000,000,000,000 kg
Jupiter's Moons
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Last Updated: 03.30.04