Galilean Moons

The Galilean Moons are the 4 biggest moons of jupiter, also having the biggest moon discovered in the solar system, Ganymede.

The 3 moons closest to Jupiter Io, Europa and Ganymede are in a laplace resonance which means every time Ganymede orbits jupiter once, Europa will orbit twice and Io orbits 4 times.

Io
Io is the closest galilean moon to jupiter. It is yellow and may have volcanoes.

Europa
Europa is the second closest galilean moon to jupiter. It is smaller (but denser = equal mass to other moons) than the other moons. It has a icy surface with an ocean below the ice sheets, which is good for life, but the temperatures are very cold and there is a lot of radiation from Jupiter.

Ganymede
Ganymede is the biggest moon and the third galilean moon from jupiter. It is the biggest moon, but is not dense as Io and Europa. It has a small magnetic field because of the core being liquid (by heating up) from tidal heating. It is similar to Europa, it has an icy sheet and rocky surface and a very deep salty water ocean below the surface.

Callisto
Callisto is the fourth galilean moon from jupiter, it is pretty big but isn't as dense as Io and Europa, having a similar density as Ganymede. It has lots of bright craters on its rocky surface. It may have a water ocean and ice sheet.