cometa

A comet, or cometa in some languages, is a small body of ice, dust, and rocky material that orbits the Sun. Comets are often described as dirty snowballs or icy dirty snowballs, reflecting a composition that has changed little since the early Solar System.

A comet’s structure typically includes a solid nucleus, usually a few kilometers to tens of kilometers across, a surrounding coma of gas and dust, and one or more tails. The tails form when solar heating causes ices to sublimate as the comet nears the Sun. An ion (gas) tail is pushed by the solar wind and points directly away from the Sun, while a dust tail follows the comet’s orbit, often appearing curved.

Most comets originate in the outer Solar System. Short-period comets come from the Kuiper Belt and have orbital periods less than about 200 years, while long-period comets originate from the distant Oort Cloud and may have periods spanning thousands to millions of years.

Observationally, comets become visible as they brighten near perihelion, sometimes developing dramatic tails that can extend millions of kilometers. They are of interest scientifically because they preserve relatively pristine material from the early Solar System, offering clues about its formation and chemical evolution. Missions such as Rosetta, which studied comet 67P/Churyumov–Gerasimenko, and Deep Impact, which impacted comet Tempel 1, have provided in-depth data on cometary composition and activity.

Note: In Spanish, the word cometa can also mean kite, so context is important for translation.