Io in Orbit
This amazing image from NASA's Cassini spacecraft shows Jupiter's volcanic moon Io in orbit around the giant planet. Jupiter's churning cloud belts can be seen in the background. Io orbits so close to Jupiter that the giant planet's gravity stretches it. The friction generates heat, which creates volcanoes. In fact, Io is the only object in the Solar System besides Earth that is known to have active volcanoes. Cassini snapped this image as it passed Jupiter on its way to Saturn.
NASA / JPL / University of Arizona