Europa and Jupiter from Voyager 1
What are those spots on Jupiter? Largest and furthest, just right of center, is the Great Red Spot -- a huge storm system that has been raging on Jupiter possibly since Giovanni Cassini 's likely notation of it 352 years ago . It is not yet known why this Great Spot is red . The spot toward the lower left is one of Jupiter's largest moons: Europa . Images from Voyager in 1979 bolster the modern hypothesis that Europa has an underground ocean and is therefore a good place to look for extraterrestrial life . But what about the dark spot on the upper right? That is a shadow of another of Jupiter's large moons: Io . Voyager 1 discovered Io to be so volcanic that no impact crater s could be found. Sixteen frames from Voyager 1's flyby of Jupiter in 1979 were recently reprocessed and merged to create the featured image . Forty years ago today, Voyager 1 launched from Earth and started one of the greatest explorations of the Solar System ever. Free 40th Anniversary Downloads: Voyager Posters