On February 5, 1979, Voyager 1 made its closest approach to Jupiter since early 1974 and 1975 when Pioneers 10 and 11 made their voyages to Jupiter and beyond. Voyager 1 completed its Jupiter encounter in early April, after taking almost 19,000 pictures and recording many other scientific measurements. Although astronomers had studied Jupiter from Earth for several centuries, scientists were surprised by many of Voyager 1 and 2′s findings. They now understand that important physical, geological, and atmospheric processes go on that they had never observed from Earth. Discovery of active volcanism on the satellite Io was probably the greatest surprise. It was the first time active volcanoes had been seen on another body in the solar system. Voyager also discovered a ring around Jupiter. Thus Jupiter joins Saturn, Uranus, and Neptune as a ringed planet — although each ring system is unique and distinct from the others.
Image and text courtesy of NASA and the NASA Marshall Space Flight Center.