Saturn’s ring gaps arise from orbital resonances with its moons

Evidence

Suppose that there were no gaps initially. The moons, circling with definite periods, tug harmlessly on all the ring particles, like a child pulling too often on a bell tower rope. Harmlessly, that is, unless the frequency of the tugs is just right. Different orbits in the ring go around at a continuous range of different periods: the closer a particle is to the planet, the faster it circulates. Therefore, particles in some orbits will have periods in exact integer ratio—for example, 2:3—with a particular moon. Particles finding themselves in such a resonance receive the tugs at the same time during each orbit. As Galileo implied, even a child’s well-timed tugs can add up resonantly. Here, they add up to cause the orbit to wander from its appointed lane. — Eric J. Heller, Why You Hear What You Hear- An…, 925

Categorization

• DEFINE: Beautifully explains orbital resonance in the concrete setting of ring particles whose orbital period is an integer ratio of a moon’s period, with the bell-rope analogy making cumulative tugs intuitive.