Kometen

Kometen are small icy bodies that travel through the Solar System on highly elongated orbits. When their orbits bring them close to the Sun, heat causes ices to sublimate, releasing gas and dust that form a glowing coma around the nucleus and often one or more tails that point away from the Sun.

Composition and structure: The nucleus is a porous mixture of ice, rock, and dust, typically ranging from a few hundred meters to several kilometers across. Surrounding the nucleus, the coma can extend thousands to millions of kilometers. The visible tails include an ion (gas) tail shaped by the solar wind and a dust tail influenced by radiation pressure, both directed away from the Sun.

Origins and orbits: Most comets originate in the Kuiper Belt or the distant Oort Cloud. Their orbits are highly eccentric, leading to passages near the inner planets. Short-period comets complete revolutions in less than 200 years and are usually linked to the Kuiper Belt, while long-period comets can have orbital periods of thousands to millions of years and are often associated with the Oort Cloud. Gravitational interactions can alter or eject comets from the Solar System.

Observation and significance: Comets have been observed since antiquity and are important to the study of the early solar system because they preserve primitive material. They are targets for space missions and ground-based observations, and their appearances—from naked-eye comets to spectacular spectacle—have influenced culture and science alike.