Goals: Voyager 1 and 2 were designed to take advantage of a rare planetary alignment to explore the outer solar system. Voyager 1 targeted Jupiter and Saturn before continuing on to chart the far edges of our solar system.
During the Jupiter leg of its journey, Voyager 1 was to explore the giant planet, its magnetosphere and moons in greater detail than the Pioneer spacecraft that preceded it. Voyager 1 was not only to study Jupiter, but to use it as a springboard to Saturn, using the gravity-assist technique.
Accomplishments: Voyager 1 succeeded on all counts, with the single exception of experiments using its photopolarimeter, which failed to operate. Jupiter's atmosphere was found to be more active than during the visits of Pioneer 10 and 11, sparking a rethinking of the earlier atmospheric models which could not explain the new features. The spacecraft imaged the moons Amalthea, Io, Europa, Ganymede, and Callisto, showing details of their terrain for the first time.
Possibly the most stunning of Voyager 1's discoveries was that Io has extremely active volcanoes, powered by heat generated by the stretching and relaxing the moon endures every 42 hours as its elliptical orbit brings it closer to and then farther from Jupiter. This finding revolutionized scientists' concept of the moons of the outer planets. The spacecraft also discovered a thin ring around the planet (then making it the second planet known to have a ring), and two new moons: Thebe and Metis.
Voyager 1 entered interstellar space in August 2013.