What are comets?

 By Mahesh Paudyal

Comets are small, fragile, irregularly shaped bodies composed of a mixture of non-volatile grains and frozen gases. They usually follow highly elongated paths around the Sun. Most become visible, even in telescopes, only when they get near enough to the Sun for the Sun's light to start evaporating the volatile gases, which in turn blow away small bits of the solid material. These materials expand into an enormous escaping atmosphere called the coma, which becomes far bigger than a planet, and they are forced back into long tails of dust and gas by radiation and charged particles flowing from the Sun. Comets are cold bodies, and we see them only because the gases in their comae and tails fluoresce in sunlight and because of sunlight reflected from the solids. Comets are regular members of the solar system family, gravitationally bound to the Sun. They are generally believed to be made of material, originally in the outer part of the solar system, that didn't get incorporated into the planets – leftover debris. It is the very fact that they are thought to be composed of such unchanged primitive material that makes them extremely interesting to scientists who wish to learn about conditions during the earliest period of the solar system.

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