Question

Astronomy:

Saturn’s rings pose a mystery to astronomers; they should fall back to the planet due to being inside Saturn’s Roche Limit. This means they should be relatively young. How do you explain this?

Answer 1

Even though Saturn's rings are within its Roche limit, yet they do not fall back into the planet due to the influence of Saturn's "shepherd moons". A shepherd moon is a small natural satellite, revolving the planet, which pulls on the particles in the rings of the planet by its gravitational force in order to contain the particles well within the ring and preventing them from falling back into the planet subjected to the gravitational pull of the planet. Saturn's "shepherd moons" include Prometheus (pulling on F ring particles to keep them contained in the ring), Daphnis, Pan, Janus and Epimetheus.( each of these moons are helping to contain the particles of one or the other ring)

As a matter of fact, particles of Saturn's D ring are actually falling into the planet presently. However, these shepherd moons are preventing the particles of the other rings, with their gravitational pull, from falling into the planet by revolving closer to these rings.