Ganymede
- Largest of the Galilean moons
- Made of ice
- Has a great deal of cratering
- $\frac{1}{4}$ of the surface seems old (heavily cratered) and the rest formed more recently
- Has differentiated like the terrestrial planets
- Has a magnetic field
- Signature of a partially molten interior
- Tidal forces from Jupiter have probably helped heat its interior and trigger major convulsions on its crust