Galileo's prime mission ended on December 7, 1997. With more to learn, and the spacecraft in
good health, NASA approved a two-year study called "GEM" -- the Galileo Europa Mission. For
fourteen more orbits, the spacecraft focused on ice, water, and fire: the icy moon Europa, which
might have an ocean; Jupiter's majestic thunderstorms; and the fiery volcanoes of Io.
The spacecraft came so close to Europa that if there were something there the size of a school
bus, Galileo would have detected it. The additional observations of Europa supported the theory
that an ocean of water currently exists below the surface. NASA began considering plans for
future missions to orbit Europa, and perhaps to send a lander.
Approaching Io --- Jupiter's innermost moon --- meant surviving Jupiter's intense radiation,
so these encounters were saved until last. When radiation upset the spcecraft's computer,
engineers worked all night to get them back on line. But Galileo came through again, and even
discovered a lava fountain erupting on Io.
These successful flybys led to another exciting mission --- the Galileo Millennium Mission,
extending into 2001. The data are collected on Io and Europa, and studies made of the effects
of radiation on a spacecraft close in to Jupiter. The Cassini spacecraft, on its way to Saturn,
swings by Jupiter in late 2000 and for a few weeks, both spacecraft observe the giant of our Solar
System.
The Future: Jupiter Icy Moons Orbiter 
Next: The Spacecraft
