Galileo was the first NASA mission to orbit an outer planet when it entered orbit around Jupiter on December 7, 1995.
NASA launched Galileo in 1989, and the spacecraft used gravity assists at Venus and Earth to reach Jupiter. It released an atmospheric probe that descended into Jupiter’s clouds and measured temperature, pressure, winds, and chemical composition.
The orbiter studied Jupiter’s atmosphere, magnetosphere, rings, and major moons. Its observations provided strong evidence that Europa, Ganymede, and Callisto have subsurface oceans or layers of liquid water beneath their icy surfaces.
Galileo operated for almost eight years at Jupiter. NASA deliberately sent it into Jupiter’s atmosphere in 2003 to prevent any accidental impact with Europa and possible contamination.