Final answer:
Saturn's rings are, on average, 20 meters thick from top to bottom. They are composed primarily of water ice particles that range in size and create an ethereal appearance.
Step-by-step explanation:
You asked how thick Saturn's rings are from top to bottom. The correct answer is that the average thickness of Saturn's main rings is only about 20 meters. This is quite thin compared to their vast width extending up to 70,000 kilometers across.
Moreover the rings are made predominantly of water ice varying in size from tiny sand grains to large boulders comparable to the size of houses. The rings may appear as a spectacular cloud of ice particles from up close varying in size and loosely clumped together in some areas.