Planet Classifications

Star Trek employs a planetary classification system. Although this is not a true planetary classification system but a planetary atmosphere classification system.

First, several classes are suitable for unprotected breathing (classes L and M) or nearly so (classes H, K, and N). All of these are listed as classes of environments for Galaxy-class starships in the ST: TNG Technical Manual.

Second, the use of single letters implies a relatively small number of classes. However, planets where humans can breath are a tiny fraction of possible planetary environments, but they are a significant fraction of those of dramatic interest to Federation visitation. Third, single classes have included a broad range of sub-stellar objects: Class-M has been applied to planets like Earth and to asteroids. These are very different objects astronomically, but as shown by the lack of asphyxiated crew members share a breathable atmosphere. The best explanation is that these classes identify the nature of the atmosphere.

	Class A* - Gas Super giant Planets of this class are usually found in a star's outer or "cold zone". They are typically 140 thousand to 10 million kilometers in diameter and have high core temperatures causing them to radiate heat. Low stellar radiation and high planet gravity enables them to keep a tenuous surface comprised of gaseous hydrogen and hydrogen compounds.
	Class B" - Gas Giant Class B Planets are usually found in a star's outer or "cold zone". They are typically 50 thousand to 140 thousand kilometers in diameter and have high core temperatures but do not radiate much heat. Low stellar radiation and high planet gravity enables them to keep a tenuous surface comprised of gaseous hydrogen and hydrogen compounds.
	Class C* - Reducing Planets of this class are usually found in a star's "habitable zone". They are typically 10 to 15 thousand kilometers in diameter. They have high surface temperatures due to the "greenhouse effect" caused by their dense atmospheres. The only water found is in vapor form.
	Class D* - Geo Plastic Planets of this class are usually found in a star's "habitable zone". They are typically 10,000 to 15,000 kilometers in diameter. They have a molten surface because they have been recently formed. The atmosphere contains many hydrogen compounds and reactive gases. Class D planets eventually cool, becoming Class E.
	Class E* - Geo Metallic Planets of this class have a molten core and are usually found in a star's "habitable zone". They are typically 10,000 to 15,000 kilometers in diameter. Their atmospheres still contain hydrogen compounds. They will cool further eventually becoming Class F.
	Class F* - Geo Crystalline Class F planets are usually found in a star's "habitable zone". They are typically 10 to 15 thousand kilometers in diameter and have surfaces that are still crystallizing. Their atmospheres still contain some toxic gases. They will cool eventually becoming Class C, M or N.
	Class G* - Desert Planets of this class can be found in any of a star's zones. They are typically 8 to 15 thousand kilometers in diameter. Their surfaces are usually hot. Their atmospheres contain heavy gases and metal vapours.
	Class H - Geo-Thermal Planets of this class are usually found in a star's "habitable zone" or "cold zone". They are typically 1,000 to 10,000 kilometers in diameter. They have partially molten surfaces and atmospheres that contain many hydrogen compounds. They cool becoming Class L.
	Class I* - Asteroid / Moon Planetary bodies of this class can be found in any of a star's zones. They are usually found in orbit of larger planets or in asteriod fields. They are typically 100 to 1,000 kilometers in diameter. They have no atmospheres. Their surfaces are barren and cratered.
	Class J - Geo-Morteus Planets of this class are found in a star's "hot zone". They are typically 1,000 to 10,000 kilometers in diameter. They have high surface temperatures due to the proximity to the star. Their atmospheres are extremely tenuous with few chemically active gases.
	Class K - Adaptable Planets of this class are usually found in a star's "habitable zone". They are adaptable for humanoid colonization through the use of pressure domes and other life support devices. They are typically 5,000 to 10,000 kilometers in diameter. They have thin atmospheres. Small amounts of water are present.
	Class L - Geo-Inactive Planets of this class are usually found in a star's "habitable zone" or "cold zone". They are typically 1,000 to 10,000 kilometers in diameter. Low solar radiation and minimal internal heat usually result in a frozen atmosphere.
	Class M - Terrestrial Planets of this class are found in a star's "habitable zone". They are typically 10,000 to 15 thousand kilometers in diameter. They have atmospheres that contain oxygen and nitrogen . Water and life-forms are typically abundant. If water covers more than 97% of the surface, then they are considered Class N.
	Class N - Pelagic Class N planets are usually found in a star's "habitable zone". They are typically 10,000 to 15 thousand kilometers in diameter. They have atmospheres that contain oxygen and nitrogen . Water and life-forms are typically abundant. If water covers less than 97% of the surface, then they are considered Class M.
	Class O* - Earth-like in mass but closer to its sun's hot zone. Has an oxygen/ nitrogen atmosphere. Temperatures average 50C up to the boiling point of water (depending on pressure). Most water exists as vapour in atmosphere. Can become class Q if greenhouse gases accumulate.
	Class P* A young world about the mass of Earth orbiting in the habitable zone. Atmosphere lacks oxygen, but nitrogen and organic compounds are present. Liquid water will be present as long temperatures and pressures remain within tolerances. May become classes L-O or Q.
	Class S - Near Star Planets of this class are usually found in a star's "cold zone". They are typically 50 million to 120 million kilometers in diameter and have high core temperatures causing them to radiate heat and light. These are the largest possible planets, because most planetary bodies that reach this size do become stars.
	Class T* - Gas Ultragiant Planets of this class are usually found in a star's "cold zone". They are typically 10 to 50 million kilometers in diameter. They have high core temperatures causing them to radiate enough heat to keep water in a liquid state.
	Class Y - Demon Class Y - Demon Planets and planetoids of this class can be found in any of a star's zones. They are typically 10,000 to 15 thousand kilometers in diameter. Atmospheric conditions are often turbulent and saturated with poisonous chemicals and thermionic radiation. Surface temperatures can reach in excess of 500 K.
Starfleet Note: Communication is frequently impossible, and transport may be difficult. Simply entering orbit is a dangerous prospect. No known environment is less hospitable to humanoid life than a Class Y planetary body. Conjectural planetary classes annotated with * Class A Class B Class C Class E Class F Class G Class I Class O Class P Class S Class T The Star Trek: Star Charts book, which was authored and advised by Trek staffers, lists many other planetary classes which may one day be recognized onscreen, but as of now they remain conjectural.

Data taken from the Star Trek Encyclopedia
Further information obtained from the Jet Propulsion Laboratory. Copyright
California Institute of Technology, Pasadena, CA. All rights reserved.

Last edited by Adge - December 2004