Why are our planets in the solar system all on the same disc/plane/layer?
I've noticed this in many pictures, Planets are shown with a single ring around them (in some particular plane). Taking extreme case... As gravity should act in all the directions, such planets must be covered with asteroids all around them. Not just single ring in some single plane..!
So, My question is: Why don't planets have many rings instead of just a single ring..?