Undergrad Are orbital resonances constructive or destructive?

[smithpa9]

If I understand correctly, orbital resonances of some of Saturn's moons are responsible for clearing out gaps in Saturn's ring structure (like the Cassini division). But I've also read that Neptune and Pluto are in a roughly 2:3 orbital resonance. So, do orbital resonances pull matter out of a stable orbit (thus creating ring gaps on Saturn)? Or do they lock objects into a stable pattern (Neptune/Pluto)? Or do they really do both? And if both, how can you explain that seeming contradiction? Thanks!

 

[pbuk]

There is no contradiction. In order for some orbits to be relatively stable, others must be relatively unstable (otherwise all orbits would be equally stable). Over time, bodies move from relatively unstable trajectories to relatively stable ones.