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
Mission: Earth, Voyage to the Home Planet pictures from the radar capture. He describes his observations while looking at the Earth from space, for example he says, "Maybe more than any other sight from space, lightning gives the decided impression that the Earth is alive, a living organism". He described aurora phenomena as, "shimmering fingers of green light reaching up from the dark ocean, an arc of light around the South Magnetic Pole". June English provides contextual information about Jones' mission. "Mission: Earth, Voyage to the Home Planet" received a positive review from journalist Rebecca O'Connell, who wrote in the "Pittsburgh Post-Gazette", "The authors convey the awe