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
Surveyor 3 panspermia, but more importantly, it led NASA to adopt strict abiotic procedures for space probes to prevent contamination of the planet Mars and other astronomical bodies that are suspected of having conditions possibly suitable for life. Most dramatically, the "Galileo" space probe was deliberately destroyed at the end of its mission by crashing it into Jupiter, to avoid the possibility of contaminating the Jovian moon Europa with bacteria from Earth. The "Cassini" probe also impacted Saturn at the end of its mission in 2017. However, independent investigators have challenged the claim of surviving bacteria on Surveyor 3 on the Moon.