comète

A comète, the French term for a comet, is a small solar system body composed largely of volatile ices, dust and rock that orbits the Sun. The heat of the Sun can sublimate the ices, releasing gas and dust that form a surrounding coma and, in many cases, one or more tails that extend away from the Sun.

The nucleus is the solid core, typically a few kilometers across. The coma is a cloud of gas and dust produced by sublimation, and it can reach thousands of kilometers in diameter. The ion tail consists of ionized gases swept directly away from the Sun by the solar wind, while the dust tail is broader and follows a curved path influenced by radiation pressure and the comet’s motion.

Comets originate from two main reservoirs. Short-period comets come from the Kuiper Belt beyond Neptune and have orbital periods of decades to a few centuries. Long-period comets originate in the distant Oort Cloud and can have highly elongated orbits with return times ranging from thousands to millions of years. Their orbits are often highly inclined and eccentric.

The study of comets provides insight into the early solar system, preserving material from its formation. They have been observed since antiquity and are now investigated with telescopes and spacecraft, which study their composition, nucleus activity, and interactions with the solar wind.