|AAPT Winter Meeting 2006|
Ganymede is the only moon with an internal magnetic field. Jupiter's rotation period is 11 h. The magnetic axis is not aligned with the rotation axis. This creates a messy plasma. The Galileo spacecraft has a mass of 2 tonnes. There is a fixed part for antennas, and a rotating part with a 20 s period. Two magnetometers are mounted on long arms 15 m apart. Two are needed to correct for the magnetic field generated by Gitself.
The planned launch in 1986 was delayed by the Challenger disaster. It was launched 3 y late in 1989 on Atlantis. The orbit was planned to use a slingshot effect from Earth's gravity to gain speed. Ganymede has a small magnetosphere inside Jupiter's magnetosphere, creating a region with strangle plasma properties.
On it's way, Galileo photographed the asteroid Ida, which has a moon Dactyl.