Four of its previous 31 close flybys of Jupiter's moons have been by Io. After eight Europa encounters, mission controllers flew the spacecraft past Jupiter's moon Callisto four times. That path nudged the probe through the Io torus, a giant doughnut-shaped collection of charged particles that surrounds Jupiter's moon Io. Researchers hoped to learn as much about the torus as they can, including what creates it and what effect it has on Jupiter's many other moons. Galileo is to fly near the small inner moon Amalthea once before a mission-ending plunge into the crushing pressure of Jupiter's atmosphere in 2003.
Scientists are extremely pleased by what the probe has discovered.
Detecting a magnetic field, stronger than the planet Mercury's, around Jupiter's largest moon, Ganymede. Learning that Europa, Io and Ganymede all have metallic cores. Oddly, Callisto does not. Observing massive volcanic eruptions on Io, including one that covered an area the size of Arizona in four months. NASA's Deep Space Network, wtih three huge antenna sites on Earth, provides the communication link for interplanetary spacecraft.