COMET
A comet is a small body of frozen gas, rock, and dust, usually with a highly eccentric orbit. While frozen, a comet is fairly compact, rarely more than a few kilometers across. However, when a comet approaches a star, the radiant warmth causes the frozen materials within to escape, giving the comet a brightly glowing atmosphere (known as the coma). As it travels, the comet will leave its signature trail of dust in its wake.
CLASS A: NON-PERIODIC
CLASS A1: EJECTION TRAJECTORY A comet with an ejection-trajectory has an eccentricity so large that it will only make one pass through a star system before heading into interstellar space.
CLASS A2: NEAR-PARABOLIC A near-parabolic comet is still gravitationally bound to a star system (usually in the outermost reaches), but with an orbital period of over 1,000 years.
CLASS B: LONG-PERIOD
A comet with a period between 200 and 1,000 years is considered long-period. They typically reside within a star system's Kuiper Belt.
CLASS C: PERIODIC
A comet with an orbital period between 20 and 200 years. They are often found between 5 and 40 AU from a star and are usually long-period comets that have migrated inward over the eons.
CLASS D: SUNGRAZER
A sungrazer is a comet found within a single AU of a star. They have an orbital period of less than 20 years and are often responsible for the meteor showers seen on inhabited worlds across the universe.