Uranus has a system of rings much smaller than Saturn; in order for the rings to stay condensed, they need shepherd moons, such as Cordelia and Ophelia, which orbit the planet on either side of the last ring. All of Uranus' rings have shepherd moons keeping them in place.
The biggest moon of Uranus, Titania, measures only half the size of Earth's moon. Some of Uranus' moons, such as Caliban and Prospero have retrograde orbits, meaning their orbits run opposite to the spin of the planet. Because of their retrograde orbits, these moons are thought to be captured asteroids that came too close to the planet and became locked in its gravitational pull.Learn more about Planets