Jupiter’s magnetosphere

Jupiter’s magnetosphere has been simultaneously sampled by two spacecraft, Galileo (already on patrol in the Jupiter system) and Cassini–Huygens (headed toward Saturn). Just as Cassini was approaching Jupiter in January 2001, other Earthbound observatories, including radio telescopes and the Hubble (optical) and Chandra (x-ray) satellites, were turned to the giant planet. The Sun also cooperated: Three interplanetary shock waves in the solar wind swept by. The two spacecraft caught Jupiter’s magnetosphere in the act of being compressed. That compression produced strong electric fields and therefore particle accelerations, which brightened Jupiter’s auroras. Internal magnetospheric dynamics caused other observed auroral brightenings and a wind of neutral atoms—formed from ions spewed by Io’s volcanic eruptions—sent outward against the incoming solar wind. Such energetic neutral atoms had not been directly observed before. The flyby also provided the first opportunity to observe electrons above 50 MeV trapped in Jupiter’s radiation belts. Shown here is the synchrotron radiation from those electrons, with a superimposed Hubble image of Jupiter. (Seven articles in Nature 415 , 985 ff, 2002 http://dx.doi.org/10.1038/415985a .)