What is a comet?

Comets are basically dusty snowballs which orbit the Sun. They are made of ices, such as water, carbon dioxide, ammonia and methane, mixed with dust. These materials came from the time when the Solar System was formed. Comets have an icy center (nucleus) surrounded by a large cloud of gas and dust (called the coma). The coma is created as the ice in the nucleus is warmed by the Sun and vaporizes. Comets can develop two tails as they travel closer to the Sun: a straight gas tail and a curved dust tail. The gas tail is created by the solar wind, pushing gas away from the comet's coma and pointing straight back from the Sun. The dust in the coma is not affected by magnetic fields but is vaporized by the Sun's heat, and forms a curved tail which follows the comet's orbit.