NASA mission to study Jupiter and its Galilean satellite s with an orbiting spacecraft and an atmospheric probe, launched in 1989.
Though the failure of its high-gain antenna resulted in its data being transmitted back to Earth very slowly, the mission returned a wealth of valuable information. En route to Jupiter, the craft took the first detailed images of two asteroids. On its arrival in 1995, its atmospheric probe descended by parachute into Jupiter's upper cloud layers, detecting large thunderstorms. In a series of flybys of the Galilean moons, the orbiter observed volcanoes on Io hotter than any on Earth and found evidence of a liquid ocean below Europa's icy surface, a magnetic field around Ganymede, and a possible subsurface ocean on Callisto.