Final answer:
Planetary rings are composed of countless individual particles that orbit around a planet, notably water ice in the case of Saturn's rings. These rings are not solid sheets but a collection of various sized ice fragments with complex structures.
Step-by-step explanation:
The nature of planetary rings is best described as composed of countless individual particles, not as solid sheets or solid rings. Planetary rings appear to be continuous when viewed from a distance, but they are essentially vast numbers of small particles, each following its own orbit around the planet. For instance, Saturn's rings are made up of icy particles that can vary in size, with some being as small as ping-pong balls, while others can be as large as basketballs. These particles are primarily made of water ice, and the structure and dynamics of these rings are influenced by their interactions with nearby moons and the planet's own gravitational field.