The disk of matter you're describing is called a planetary ring system.

Here's a breakdown:

* Planetary ring systems are collections of dust, rock, ice, and other particles that orbit a planet.

* These particles range in size from micrometers (a few millimeters) to several hundred meters.

* The rings are held together by the planet's gravity and often have thin, flat structures.

* The most famous example is Saturn's ring system, which is composed of primarily ice particles.

Let me know if you'd like to know more about planetary ring systems!