cometary

Cometary is an adjective used in astronomy to describe phenomena, features, or processes related to comets—small, icy bodies that orbit the Sun and become visibly active as they approach perihelion.

A typical comet has a solid nucleus composed of ice, dust, and rocky material; when heated, ices sublimate, creating a surrounding atmosphere called the coma. The coma often extends thousands of kilometers and is the source of the comet's tails.

The dust tail is curved and follows the comet's trajectory, while the ion or gas tail is pushed straight away from the Sun by solar wind.

Orbits are generally highly elongated; most comets originate from the Kuiper Belt or the Oort Cloud, and are classified as short-period or long-period depending on their orbital period.

Activity depends on distance from the Sun; aside from water, other volatile ices release gases such as carbon dioxide, carbon monoxide, methane, and ammonia. Jets and fragmentation can occur, altering or breaking up a nucleus.

The study of cometary material offers clues about the early solar system and the delivery of water and organic compounds to the terrestrial planets.