The rings probably formed primarily because one or more small moons broke up close to Saturn. This breakup could have been the result of a collision with a comet or asteroid, or with another moon in close orbit around Saturn. Over millions of years, the moon bits and cometary ice chunks spread out into the complex ring system that exists today. Ring formation can also start or be sped up if a large enough moon, asteroid, or comet comes close enough to Saturn that the gravitational pull of Saturn gently breaks it apart. This can happen when the difference between gravity’s pull on the side facing Saturn and its pull on the side facing away from Saturn is enough to tear the object apart. After it is pulled apart, the smaller particles will begin to collide with each other and with preexisting ring particles. This slowly grinds them down in size and spreads them out, gradually adding to Saturn’s rings.