 The first spacecraft to visit Jupiter was Pioneer 10 in 1973 , followed a year later by Pioneer 11 . Aside from taking the first close @-@ up pictures of the planet , the probes discovered its magnetosphere and its largely fluid interior . The Voyager 1 and Voyager 2 probes visited the planet in 1979 , and studied its moons and the ring system , discovering the volcanic activity of Io and the presence of water ice on the surface of Europa . Ulysses further studied Jupiter 's magnetosphere in 1992 and then again in 2000 . The Cassini probe approached the planet in 2000 and took very detailed images of its atmosphere . The New Horizons spacecraft passed by Jupiter in 2007 and made improved measurements of its and its satellites ' parameters . 
