Comets and asteroids are both objects that orbit the sun, but they differ in their composition, appearance, and behavior. Here's a brief explanation of each:

1. Comets: Comets are icy bodies that originate from the outer solar system. They are composed of frozen water, methane, ammonia, and other volatile compounds, as well as dust and rock. When a comet approaches the sun, the heat causes the ice to sublimate, or turn directly from a solid to a gas, creating a coma or atmosphere around the comet, and often a tail pointing away from the sun. Comets are often considered to be "dirty snowballs" because of their icy composition and their glowing appearance in the sky.
2. Asteroids: Asteroids are rocky bodies that orbit the sun, mostly between the orbits of Mars and Jupiter in the asteroid belt, but also found elsewhere in the solar system. They are made up of rock and metal, and some may also contain organic compounds. Asteroids range in size from small pebbles to large boulders, and some are considered to be minor planets. Unlike comets, asteroids do not have a coma or tail, and their appearance is generally dark and dull.

In summary, comets are icy bodies that develop a coma and a tail when they get close to the sun, while asteroids are rocky bodies that do not. Comets are believed to have formed in the outer solar system and to have been perturbed into orbits that bring them closer to the sun, while asteroids are thought to be remnants from the early solar system that never formed into planets.