Comets
Small objects in the solar system, consisting mainly of frozen gases and dust, resembling "dirty snowballs". A comet only becomes visible when it approaches the Sun. Gases are dissipated by the Sun's heat and excited to luminescence by the solar wind. The gas also forms the tail of the comet. Astronomers believe that a comet orbits the Sun approx. 1000 times until it is fully dissipated (see illustrations 13 and 14).