During the 1970s and 1980s, two Voyager space probes gave us unprecedented images of the jovian planets. Voyager 1 visited Jupiter and Saturn, and Voyager 2 added Uranus and Neptune to the list.
The Voyager missions also revealed volcanic activity on Io, one of Jupiter’s moons. As
for Saturn, a new, previously unknown system of rings emerged: several thousand
ringlets. Ten additional moons were discovered orbiting Uranus, which also revealed
the presence of a stronger magnetic field than had been predicted. And the Neptune
flyby led to the discovery of three planetary rings as well as six previously unknown moons. The hitherto featureless blue face of the planet was now resolved into atmospheric bands, as well as giant cloud streaks. As a result of the Voyager 2 flyby, the magnetospheres of Neptune and Uranus were detected. As with the Van Allen belts around the earth, the magnetospheres of these planets trap charged particles (protons and electrons) from the solar wind.
If only its namesake could have lived to see it. Launched in 1989, Galileo reached Jupiter in 1995 and began a complex 23-month orbital tour of the planet and its almost 400 years after the Italian astronomer first gazed on its colored bands and moons. Among the most extraordinary of
Galileo’s discoveries is a new ring of dust that has a retrograde (backward) orbit around Jupiter. About 700,000 miles (1,120,000 km) in diameter, this doughnut-shaped ring moves in the opposite direction of the rotating planet and its moons. Why does it move in this fashion? No one yet knows.
The Cassini space probe passed Jupiter in early 2001 and sent back images from its many cameras.
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