Comet.  A comet orbits around the Sun in an elliptical path. As it approaches the Sun, it appears as a faint star. When it is near the orbit of Mars, a coma, or head, develops and the first sign of a tail. The tail grows longer as the comet nears the Sun. The tail always points away from the Sun. As the comet leaves the influence of the Sun, the tail gets smaller and then disappears.

A comet is a small body from the outer reaches of the solar system similar to an asteroid but composed of ice. Often described as "dirty snowballs," they are composed largely of carbon dioxide ice, methane ice, and water ice with a mixture of dust and small stony aggregates mixed in. Comets are thought to be small pieces of debris left over from the formation of the solar system, representing a sample of the original composition of the nebula that condensed to form the Sun and all of its planets.