According to current understanding, which of the following is required in order for a planet to have rings?
A) The planet must once have had a large moon that came too close to it, shattering the moon and creating the ring particles.
B) The planet must be at least as massive as Saturn.
C) The planet must orbit its star at a distance greater than Mars orbits the Sun.
D) The planet must have many small moons that orbit relatively close to the planet in its equatorial plane.
Answer: D