Callisto: 8/10 — Might have an internal water ocean, is the most heavily cratered object in the solar system.
Io: 10/10 — Most volcanically active world in the solar system. Spews fountains of lava dozens of miles high. Might have a magma ocean.
Europa: 12/10 — Has a liquid water ocean, plumes of water vapor shooting into space, and maybe life. Very icy, very smooth.
Ganymede: 9/10 — Largest moon in the solar system (it’s bigger than the planet Mercury!), only moon with its own magnetic field.
Almathea (middle): 8/10 — Reddest object in the solar system. Feeds material to Jupiter’s Gossamer ring (yes, Jupiter has rings!)
Chaldene: 7/10 — One of Jupiter’s many retrograde moons, which means it’s a rebel that orbits in the opposite direction as the other moons. (We don't have a picture of it.)
Metis (right): 7/10 — Small but mighty. Orbits Jupiter faster than Jupiter turns on its own axis. Take that, Jupiter!
Dia: 10/10 — This sneaky moon disappeared in 2000 right after it was discovered. It didn’t turn up again until 2010. (We also don't have a picture of this one.)