"The largest moon in the solar system is Ganymede, at Jupiter. Many structures have been found on its surface that are still a mystery. During the Galileo mission to Jupiter it was discovered that Ganymede possessed a weak magnetic field. This was very surprising to planetary scientists because in small objects like moons, it is generally thought that any intrinsic field should have long since ceased to exist. Planetary scientists rely on dynamo theory to explain how planetary magnetic fields are maintained for billions of years. But magnetic dynamo theory has technical problems and especially so with a moon like Ganymede. The question of how Ganymede could still possess a magnetic field -- A dynamo requires that there be a liquid core of a conducting material such as iron and the core must support convection currents. If there is an electric current in a core consisting of a moving conducting liquid, this may generate a magnetic field. The chief problem in a small body such as Ganymede is the small core. A small sphere cools faster than a large sphere, thus a moon tends to cool rapidly over time. The heat flux out of Ganymede’s core should not be enough to keep convection operating in the core for over four billion years.In compositional convection, iron and possibly other metals would cool and condense to solid form at the top of the core and then sink to the center. In this process lighter materials such as sulfur would be driven out of the core. Thus a division of materials takes place, and when the metals condense, latent heat is released that is thought by some to be able to drive convection. This idea suffers from a significant problem that it happens at the bottom of the mantle, which is much cooler than the core. This means the heat generated by the process would be absorbed by the mantle and so it is doubtful that this process could drive a dynamo for billions of years.
There is another interesting possible structure in Ganymede that could affect its magnetic field. Planetary scientists suspect that Ganymede has a layer of liquid salt water some distance below the crust. This has been proposed to explain some of the interesting surface formations on Ganymede. However, a salt water layer is potentially an electrical conductor. So, scientists have considered whether the water layer could contribute to Ganymede’s magnetic field. A water solution, if there were an electrical current in it, would not likely produce a dynamo because very rapid fluid motion would be required. A water convection dynamo would probably not be stable, if it were even possible. However, it is possible that a water layer could cause some minor variations in Ganymede’s magnetic field. In a young age approach such as that from Russ Humphreys, the difficulties of dynamo theory are avoided and Ganymede fits into a biblical view of history." CMI
In the beginning God created the heaven and the earth.
Genesis 1:1
