The Voyager missions vastly improved our understanding of the Galilean moons , and also discovered Jupiter 's rings . They also took the first close @-@ up images of the planet 's atmosphere , revealing the Great Red Spot as a complex storm moving in a counter @-@ clockwise direction . Other smaller storms and eddies was found throughout the banded clouds ( see animation on the right ) . Two new , small satellites , Adrastea and Metis , was discovered orbiting just outside the ring , making them the first of Jupiter 's moons to be identified by a spacecraft . A third new satellite , Thebe , was discovered between the orbits of Amalthea and Io .