Collisions with neighboring particles permanently lock expelled particles out of resonance, carving ring gaps.

Evidence

A ring particle recently resonantly expelled from a traffic lane does, however, manage to find a source of friction: as a new arrival to an adjacent orbit, the particle finds itself going a shade too fast or slow and suffers very minor fenderbenders with other particles. These collisions soon settle the particle in its new orbit, safely out of resonance with the moon that kicked it out of the old orbit. All particles initially in the resonant lane will suffer this fate. The result will be a gap swept clean. This story is repeated with different moons and frequency ratios involving small integers, leading to many gaps. — Eric J. Heller, Why You Hear What You Hear- An…, 927

Categorization

• CANDY: The image of ring particles suffering ‘minor fenderbenders’ is a delightfully concrete way to explain gap formation — tweetable on its own.