When the Galileo spacecraft flew by Ganymede, to everyone's surprise, it measured a very strong magnetic field for the first time near any moon.

To generate a magnetic field, there must be conducting material inside. This may be provided either by iron, or by salt water. The conducting material must also be in motion. Motions are usually provided by hot convective motions of the conducting material itself.

The existence of a magnetic field provides further evidence that Ganymede is not completely frozen, but has either a warm iron core or a salty, subterranian ocean. This is completely uncharacteristic of an icy moon, and makes Ganymede unique.

The presence of a magnetic field provides for a different kind of interaction with the charged particles in the magnetic environment of Jupiter. Such an interaction might even include aurora.

When the Galileo spacecraft flew by Ganymede, it found something that was a big surprise to everyone -- a very strong magnetic field. This is the first time a strong magnetic field had been found near any moon.

To generate a magnetic field, there must be conducting material inside. This may be provided either by iron, or by salt water. The conducting material must also be in motion. This means that Ganymede is not completely frozen, but has either a warm iron core or a salty, hideen ocean. This is completely new idea for an icy moon, and makes Ganymede unique.

Did you know that some of the planets and moons can be magnetic? Earth is! The Galileo spacecraft found out that a moon of Jupiter, Ganymede, is magnetic too!