Comet
A chunk of frozen gasses, ice, and rocky debris that orbits a sun, comets are an exceedingly common phenomenon in the Universe; there can be trillions of comets in a single solar system.
A comet nucleus is about the size of a planetary mountain. When a comet nears its central star, heat vaporizes the icy material producing a cloud of gaseous material surrounding the nucleus, called a coma. As the nucleus begins to disintegrate, it also produces a trail of dust or dust tail in its orbital path and a gas or ion tail pointing away from the star. Comet comas can extend up to a million miles from the nucleus and comet tails can be millions of miles long.
Long-period comets
A long-period comet is a comet moving on a nearly parabolic orbit and thus having an orbital period of hundreds of thousands of years.
Comet mining
Water ice is a valuable resource to terraforming operations, which is why comets are often chased, strip-mined or even intentionally crashed into planetary atmospheres lacking oxygen.
Comets in space combat
It is possible for a starship to try to enter a comet’s tail to hide, or to land on its core. With all high-energy systems turned off, this can make a very successful disguise.
