 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 about the Jovian system , making close approaches to all of the four large Galilean moons and finding evidence for thin atmospheres on three of them , as well as the possibility of liquid water beneath their surfaces . It also discovered a magnetic field around Ganymede . As it approached Jupiter , it also witnessed the impact of Comet Shoemaker – Levy 9 . In December 1995 , it sent an atmospheric probe into the Jovian atmosphere , so far the only craft to do so . 
