Comets

Comets are ancient solar system objects much smaller in size than a typical planet or moon. Comets may be leftover chunks of material out of which planets formed billions of years ago. Comets are solid bodies consisting of a mixture of ices and rock. The ices can be frozen water, carbon dioxide, methane, ammonia, or carbon monoxide, just to name a few. When they approach the Sun, comets form an atmosphere called a coma. Comets can also form a neutral dust tail and an ion tail. The ion tail interacts with the solar wind and always points away from the Sun. The dust tail tends to follow the path of the comet behind it. Most comets orbit the Sun far away from the inner solar system in the Kuiper Belt or the Oort Cloud and are not typically visible from Earth. The orbits of comets do not necessarily lie in or near the ecliptic. When their distant orbits are perturbed, comets can enter the inner solar system. These comets are classified as single-pass or periodic depending on whether their orbits are hyperbolic, parabolic, or elliptical.