Io 's surface is young, shows practically no impact craters, and is continually being repaved by the lava exploding from its many large volcanoes . Callisto 's surface is old, shows the highest density of impact craters in the Solar System , and harbors no volcanoes or even any large mountains. Callisto 's surface is one large ice-field, laced with cracks and craters from billions of years of collisions with interplanetary debris. The high-resolution vertical band in the above mosaic was taken by the robot spacecraft Galileo currently orbiting Jupiter . The rest of the mosaic was compiled from pictures taken by the Voyager spacecraft which passed the Callisto in 1979.
Specific rights apply .