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
Exploration of Jupiter 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. The "Galileo" spacecraft was the first to have entered orbit around Jupiter, arriving in 1995 and studying the planet until 2003. During this period "Galileo" gathered a large amount of information