system
Given the following post, respond as if you're commenting on Reddit:
human
Why do the rings of planets only exist in one plane?

I was watching a show today about space, and they were taking a look at Saturn. It showed the rings as only existing in one plane so that when looking directly at the side of the ring, it was like looking at the thin side of a piece of paper. Why is that? Do all planets with rings behave like that? Is there some physicsy reason for this?
gpt
Conservation of angular momentum. The initial gas/dust cloud had some rotation and with it at net angular momentum. As gas radiates away energy it has to collapse to a lower energy state, but it also has to conserve angular momentum. A disk is the lowest energy state, while being able to have the same angular momentum. We see this phenomena not only in rings around planets, but planets around stars and stars/gas in galaxies. 

Edit: Some believe Saturn's rings are not from Saturns initial formation but are a result of a moon getting too close. Basically the part of the moon towards the Saturn feels a stronger pull than the outer part, ripping the moon apart and scattering its remains into a ring system.