Comet

A comet is a type of celestial body that is composed of rock and ice, and is usually found to be orbiting a star. If a comet orbits to close to a star, then the increased heat causes the comet to shed its mass and creates a coma and/or "tail".

In June 2151, the Earth starship Enterprise discovered the largest comet that had yet been discovered by Humans, and was named Archer's Comet after Enterprise captain, Jonathan Archer. (ENT episode: "Breaking the Ice"; TNG novel: A Time to Sow; reference book: )

In late 2266, the area near the Icarus IV comet was the focus of a battle between a Romulan Bird-of-Prey and the USS Enterprise (NCC-1701). (TOS episode: "Balance of Terror"; TOS novel: The Return)

In 2373, the USS Enterprise (NCC-1701-E) detected a class-2 comet while conducting a patrol of the Romulan Neutral Zone. (TNG movie: )