 The definitive discovery of the Jovian magnetic field occurred in December 1973, when the Pioneer 10 spacecraft flew near the planet.As of 2009 a total of eight spacecraft have flown around Jupiter and all have contributed to the present knowledge of the Jovian magnetosphere.The first space probe to reach Jupiter was Pioneer 10 in December 1973, which passed within 2.9 "R"J from the center of the planet.