What is the main difference between a comet and an asteroid?

The main distinction between a comet and an asteroid lies in their composition. Comets are composed primarily of ice, dust, and rocky materials, which is why they often develop a glowing coma and tail when they approach the Sun. The heat causes the ice to vaporize, releasing gases and dust particles that create this characteristic feature. In contrast, asteroids are predominantly made up of rocky and metallic materials, lacking the icy components that define comets. This fundamental difference in composition not only influences their physical appearances but also their behaviors when they travel through the solar system.

Understanding this distinction highlights why comets can display dramatic tails and comas while asteroids generally do not exhibit such features. The other options present mischaracterizations about size, features like tails, and the locations of these celestial bodies, which do not accurately represent the primary difference between comets and asteroids.