Which object is primarily composed of rock, ice, and frozen gas?

Comets are primarily composed of rock, ice, and frozen gases, which is a key characteristic that differentiates them from other celestial objects. The structure of a comet can be visualized as a "dirty snowball," where the ice forms the core surrounded by dust and rocky materials. When comets approach the sun, the heat causes these ices to sublimate, creating a glowing coma and sometimes a tail that can stretch for millions of kilometers. This behavior further highlights their composition and the unique interactions they have with solar radiation.

In contrast, asteroids are primarily made up of rock and metal, lacking the significant amounts of ice found in comets. Planets, on the other hand, have a much more varied composition, often including large amounts of gas and liquid, especially in the case of gas giants, but they do not typically possess the combination of ice and rock as seen in comets. Stars, being massive celestial bodies fueled by nuclear fusion, consist mostly of hydrogen and helium, which is entirely different from the composition of a comet.