cometen

Cometen, the Dutch term for comets, are small bodies in the Solar System composed mainly of ice, dust, and rocky material. Typically, a comet has a solid nucleus a few kilometers across, surrounded by a fuzzy coma. When a comet travels close to the Sun, solar heating causes volatile ices to sublimate, releasing gas and dust that form the coma and often two distinct tails: a dust tail pushed by solar radiation and an ion tail shaped by the solar wind. The tails always point away from the Sun as the comet moves along its orbit.

Most comets originate in the outer regions of the Solar System. Short-period comets have orbital periods under about 200 years and largely originate from the Kuiper Belt. Long-period comets come from the distant Oort Cloud and can take thousands of years to orbit the Sun, arriving from any direction. Halley-type comets have intermediate periods. Comets are part of a dynamic exchange of material between the outer Solar System and the inner planets.

Scientifically, comets are valuable because they preserve relatively pristine material from the early Solar System, offering clues about its formation and the distribution of ices and organic compounds. Space missions, such as Rosetta to comet 67P/Churyumov–Gerasimenko, have studied nuclei, outgassing processes, and interactions with the solar wind.

Impact on Earth is rare, but debris shed by comets can produce meteor showers when Earth crosses their orbital paths. Related topics include the Kuiper Belt and the Oort Cloud.