why the rings of Saturn are all along one line.


I would have thought all of the rings would be at different rotations around the planet, but they all bunch up together. Is that along Saturn’s equator? If so, why?

In: Physics

Gravity. As Saturn rotates and revolves around the sun, it pulls on all those little chunks and rocks. The sun also pulls, but more lightly. After millions of years of that, those uniform tugs bring them all into a uniform line, generally along the equator because that’s where both the sun’s and Saturn’s pulls would bring them. (Think of it like you hold a string tied to a rock, and I hold a string tied to the same rock. If we both pull, the rock will end up between the two of us).

Many things in astronomy work that way. Gravity tends to normalize rotations and revolutions. Note that all the major planets occupy roughly the same plane of orbit around the sun, and generally speaking most stars in the Milky Way occupy the same general rotational plane around the core. Also note that none of this is “perfect” from our perspective, it’s all a little bit off or a little bit tilted sometimes.

Most of the material in orbit around a planet formed from the same stuff as the planet itself, so it has a common angular momentum.

Imagine stuff moving in all sorts of orbits, but stuff that has intersecting orbits at big angles will hit each other over time at high speed and blast away. But stuff that’s close to the most common orbit will hit each other at slower speeds, and be more likely to just stick together and keep similar orbits.

So you get moons in these common planes close to the equators of planets.

You get rings in something called a Roche Orbit where the gravity of the planet pulls things apart while still keeping it in a common orbit.