Rare Hubble Portrait of Io and Jupiter
This image shows Jupiter's volcanic moon Io passing above the turbulent clouds of the giant planet. The conspicuous black spot on Jupiter is Io's shadow. This shadow is about the size of Io (2,262 miles or 3,640 kilometers across) and sweeps across the face of Jupiter at 38,000 mph (17 kilometers per second).
The smallest details seen on Io and Jupiter are about 100 miles across. Bright patches visible on Io are regions of sulfur dioxide frost. Io is roughly the size of Earth's moon but 2,000 times farther away.