this image, shows jupiter's volcanic moon Io passing above the turbulent clouds of the giant planet, on July 24, 1996. the conspicuous black spot on jupiter is io's shadow. the shadow is about the size of io (3,640 kilometers across) and sweeps across the face of jupiter at 17 kilometers per second.the smallest details visible on io and jupiter are about 100 miles across. io is roughly the size of earth's moon, but 2,000 times farther away.