comete

Comete, sometimes written comète in French, refers to the class of objects in the Solar System known in English as comets. These are small bodies composed largely of volatile ices mixed with dust and rocky material. When a comet approaches the Sun, solar heating causes the ices to sublimate, releasing gas and dust that form a surrounding coma and often one or more tails that extend away from the Sun.

The solid core of a comet is called the nucleus, typically measuring from a few hundred meters to several kilometers in diameter. The coma is a gas-and-dust envelope that can reach tens of thousands of kilometers, while the tails can stretch to millions of kilometers. There are two main tails: a dust tail created by solar radiation pressure and an ion (gas) tail shaped by the solar wind. Tails always point away from the Sun, regardless of the comet’s direction of travel.

Most comets originate in the outer Solar System. Short-period comets come from the Kuiper Belt or related regions, while long-period comets are believed to come from the distant Oort Cloud. Their orbits are highly eccentric and can be inclined, with some returning after only a few years and others taking many millennia.

Comets are scientifically valuable because they preserve primitive material from the early Solar System. They have also enriched Earth with water and organic compounds through past impacts. Notable space missions include Rosetta to 67P/Churyumov–Gerasimenko, Deep Impact to Tempel 1, and Stardust’s sample return from Comet Wild 2.