Magnetosphere of Jupiter By 1973 the magnetic moment was known within a factor of two, whereas the tilt was correctly estimated at about 10°. The modulation of Jupiter's DAM by Io (the so-called Io-DAM) was discovered in 1964, and allowed Jupiter's rotation period to be precisely determined. 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
Space Shuttle Atlantis after its previous mission, STS-51-J in October 1985. "Atlantis" was then used for ten flights between 1988 and 1992. Two of these, both flown in 1989, deployed the planetary probes "Magellan" to Venus (on STS-30) and "Galileo" to Jupiter (on STS-34). With STS-30 "Atlantis" became the first shuttle to launch an interplanetary probe. During another mission, STS-37 flown in 1991, "Atlantis" deployed the Compton Gamma Ray Observatory. Beginning in 1995 with STS-71, "Atlantis" made seven straight flights to the former Russian space station Mir as part of the Shuttle-Mir Program. STS-71 marked a number of firsts in human spaceflight: 100th