Final answer:
Comets are referred to as rubble piles due to their composition of multiple fragments, including ice and dust.
Step-by-step explanation:
Comets are referred to as rubble piles primarily because they are composed of multiple fragments.
Comets are made up of a mixture of ice, dust, and solid grains. These materials come together to form a loosely packed structure, giving comets their irregular shapes.
When comets pass close to the Sun, the heat causes the ice in them to evaporate, releasing gas and dust particles into space. This process can lead to the disintegration or breakup of the comet, further contributing to their rubble-like appearance.