Voyager 1 flew by Jupiter's moon Io with its closest approach taking place on March 5, 1979. During this flyby encounter, the probe discovered active volcanoes on Io, the first time active volcanoes were seen on another body in the Solar System.
The closest approach to Io, which is about 5% larger than earth's moon, was at an altitude of 20,570 km (12,780 miles) and the images revealed that Io's surface was heavily dotted with active volcanoes, plumes, and lava lakes, appearing as a "pizza-like" surface. It helped scientists determine that Io's volcanic activity supplies the material that populates the Jovian magnetosphere with sulfur, oxygen, and sodium. Voyager 1 continued to study Jupiter and its moons until April 1979 before heading to Saturn.
