 Voyager 1 began photographing Jupiter in January 1979 and made its closest approach on March 5 , 1979 , at a distance of 349 @,@ 000 km from Jupiter 's center . This close approach allowed for greater image resolution , though the flyby 's short duration meant that most observations of Jupiter 's moons , rings , magnetic field , and radiation environment were made in the 48 @-@ hour period <unk> the approach , even though Voyager 1 continued photographing the planet until April . It was soon followed by Voyager 2 , which made its closest approach on July 9 , 1979 , 576 @,@ 000 km away from the planet 's cloud tops . The probe discovered Jupiter 's ring , observed intricate <unk> in its atmosphere , observed active volcanoes on Io , a process analogous to plate <unk> on Ganymede , and numerous craters on Callisto . 
