Introduction 

Planets are labeled according to a letter nomenclature. Planetary classes near the letter M are generally more likely to support humanoid life.

Class A

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

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

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

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

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

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 crystalizing. Their atmospheres still contain some toxic gases. They will cool eventually becoming Class C, M or N.

Larger rock worlds such as Luna or Mercury in the Sol system fall into this class. Class F planets have no water or atmosphere of any kind present, but are larger than class D worlds. Dwellings on class F worlds are usually functionally indistinguishable from spacecraft environments in design.

Class G

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 vapors.

These worlds have low gravities, but poses ices or sludges (water, methane, amonia etc). Any atmosphere on a class G world is by definition unbreathable. Titan, a moon of Saturn in the Sol system, and the planet Pluto, in the Sol system are class G worlds.

Class H

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.

Extremely dry worlds, marginally inhabitable with personal atmosphere (and usually temperature) gear.

Mars in the Sol system began as a class H world. Tau Cigna V is another example.

Class I

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

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.

These worlds are "Jovian" gas giants similar to Jupiter or Saturn in the Sol system. Such worlds have crushingly high gravities and very turbulent atmospheres. This clasification also covers sub jovians such as Uranus or Neptune in the Sol system, and superjovians (brown dwarfs which orbit stars but ar not quite at the critical mass to ignite stellar fusion) like Barnard 3.

Class K

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.

These planets, although possessing Earthlike gravity, have temperatures or atmospheres preventing human settlement without presure domes and life support systems.

Venus in the Sol system, the Breen homeworld and Elba III are all examples of class K worlds.

Class L

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.

One of the large number of planets possesing oxygen - argon atmospheres. Often as with Indri VIII Class L worlds show signs of ancient terraforming.

Class M

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.

A planet habitable by humans and other compatible species within certain norms of atmosphere, temperature and gravity. These norms are quite broad.

Earth, Vulcan and Cardassia Prime are class M worlds.

Class N

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 S

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

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 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.