Planetary classifications

Natural characteristics of planets, such as age, mass and distance from their sun, place them in 20 naturally bounded classes which have been assigned an arbitrary alphabetic designation.
Location refers to the planet's relative distance from its primary star (Hot zone is closest, then Ecosphere, then Cold Zone). Depending on the star's magnitude and amount of energy it radiates, the distances of each zone from the star will vary.
A planet's mass determines its internal heat generation and - in combination with its zone - its ability to hold an atmosphere. Some planets pass through distinct stages as they form and age, which may put them in separate classes.
Evolution refers to the geological evolutionary process of the planetary body itself. It does not refer to life-form evolution.
== Class A ==
Class A planets are small, typically 1 to 1/10 the mass of Earth, and are in their sun's cold zone. They are newly formed and their surfaces are still molten. Their atmospheres still retain many hydrogen compounds, as well as reactive gases and rock vapors. These planets will cool, becoming Class C.
* Type: Geothermal
* Age: 0 - 2 billion years
* Diameter: 1,000 - 10,000 km
* Location: Ecosphere / Cold Zone
* Surface: Partially molten
* Atmosphere: Primarily hydrogen compounds
* Evolution: Cools to become Class C
* Life-Forms: None
* Examples: Gothos
== Class B ==
Class B planets are small, typically 1/10 the mass of Earth, and are in their sun's hot zone. Due to a combination of weak gravity and strong solar radiation, their atmospheres are very tenuous, with few chemically active gases, and their surfaces are extremely hot.
* Type: Geomorteus
* Age: 0 - 10 billion years
* Diameter: 1,000 - 10,000 km
* Location: Hot Zone
* Surface: Partially molten, high surface temperature
* Atmosphere: Extremely tenuous, few chemically active gases
* Evolution: n.a.
* Life-Forms: None
* Examples: Mercury
== Class C ==
Class C planets are small, typically 1 to 1/10 the mass of Earth and are in their sun's cold zone. Due to a combination of low solar radiation and little heat, their atmospheres are permanently frozen.
* Type: Geoinactive
* Age: 2 - 10 billion years
* Diameter: 1,000 - 10,000 km
* Location: Ecosphere / Cold Zone
* Surface: Low surface temperature
* Atmosphere: Frozen
* Evolution: n.a.
* Life-Forms: None
* Examples: Pluto, Psi 2000
== Class D ==
Class D planets are small, typically 1 to 1/100 the mass of Earth, or less. Due to low gravity, they have lost their atmospheres. Their surfaces, directly exposed to radiation and meteor impact, are typically lifeless and heavily cratered.
* Type: Asteroid / Moon
* Age: 2 - 10 billion years
* Diameter: 100 - 1,000 km
* Location: Hot Zone / Ecosphere / Cold Zone; found primarily in orbit of larger planets or in asteroid fields
* Surface: Barren and cratered
* Atmosphere: None or very tenuous
* Evolution: n.a.
* Life-Forms: None
* Examples: Moon (Sol IIIa), Lunar V (Bajor VIIe)
== Class E ==
Class E planets are typically of about the mass of Earth and are in their sun's habitable zone. They are newly formed, and their surfaces are still molten. Their atmospheres still retain many hydrogen compounds, as well as reactive gases and rock vapors. These planets will cool, becoming Class F.
* Type: Geoplastic
* Age: 0 - 2 billion years
* Diameter: 10,000 - 15,000 km
* Location: Ecosphere
* Surface: Molten, high surface temperature
* Atmosphere: Hydrogen compunds and reactive gases
* Evolution: Cools to become Class F
* Life-Forms: Carbon-cyle (ie. Excalbian)
* Examples: Excalbia
== Class F ==
Class F planets are typically about the mass of Earth and are in their sun's habitable zone. They are recently formed, and their surfaces are thin. Their atmospheres still contain some hydrogen compounds. These planets will cool further, becoming Class G.
* Type: Geometallic
* Age: 1 - 3 billion years
* Diameter: 10,000 - 15,000 km
* Location: Ecosphere
* Surface: Volcanic eruptions due to molten core
* Atmosphere: Hydrogen compounds
* Evolution: Cools to become Class G
* Life-Forms: Silicon-based (ie. Horta)
* Examples: Janus IV
== Class G ==
Class G planets are typically about the mass of Earth and are in their sun's habitable zone. They are younger than the Earth, and their surfaces are still crystallizing. Their atmospheres retain small amounts of toxic gases. As these planets continue cooling they may become other classes.
* Type: Geocrystalline
* Age: 3 - 4 billion years
* Diameter: 10,000 - 15,000 km
* Location: Ecosphere
* Surface: Still crystallizing
* Atmosphere: Carbon Dioxide, some toxic gases
* Evolution: Cools to become Class K, L, M, N, O, or P
* Life-Forms: Primitive single-celled organisms
* Examples: Delta Vega
== Class H ==
Class H planets are typically about the mass of Earth and are in their sun's hot zone. Their gravity allows them to retain an atmosphere of heavy gases and metal vapors, but due to strong solar radiation, their surfaces are very hot.
* Type: Desert
* Age: 4 - 10 billion years
* Diameter: 8,000 - 15,000 km
* Location: Hot Zone / Ecosphere / Cold Zone
* Surface: Hot and arid, little or no surface water
* Atmosphere: May contain heavy gases and metal vapors
* Evolution: n.a.
* Life-Forms: Drought- and radiation-resistant plants, animal life
* Examples: Rigel XII, Tau Cygna V
== Class I ==
Class I planets (Gas Supergiants) are very large, typically 300 to 1,000 times the mass of Earth, and are their sun's cold zone. Low solar radiation and high gravity have allowed them to keep thick atmospheres of hydrogen compounds. High core temperatures cause them to radiate heat.
* Type: Gas Supergiant
* Age: 2 - 10 billion years
* Diameter: 140,000 - 10 million km
* Location: Cold Zone
* Surface: Tenuous, comprised of gaseous hydrogen and hydrogen compounds; radiates heat
* Atmosphere: Zones vary in temperature, pressure and composition; water vapor may be present
* Evolution: n.a.
* Life-Forms: Unknown
* Examples: Q'tahL, Jupiter
== Class J ==
Class J planets (Gas Giants) are large, typically 10 to 100 times the mass of Earth, and are in their sun's cold zone. Low solar radiation and high gravity have allowed them to keep thick atmospheres of hydrogen and hydrogen compounds.
* Type: Gas Giant
* Age: 2 - 10 billion years
* Diameter: 50,000 - 140,000 km
* Location: Cold Zone
* Surface: Tenuous, comprised of gaseous hydrogen and hydrogen compounds; radiates some heat
* Atmosphere: Zones vary in temperature, pressure and composition
* Evolution: n.a.
* Life-Forms: Hydrocarbon-based (Jovian)
* Examples: Saturn
== Class K ==
Class K planets are small, typically 1 to 1/10 the mass of Earth, and are in their sun's habitable zone. Due to weak gravity, their atmospheres are tenuous, but water is usually present.
* Type: Adaptable
* Age: 4 - 10 billion years
* Diameter: 5,000 - 10,000 km
* Location: Ecosphere
* Surface: Barren, little to no surface water
* Atmosphere: Thin, mostly carbon dioxide
* Evolution: n.a.
* Life-Forms: Primitive single-celled organisms; adaptable for humanoid colonization through the use of pressure domes
* Examples: Mars, Mudd
== Class L ==
Class L planets are small, typically 1 to 1/10 the mass of Earth, and are in their sun's habitable zone. Their atmospheres are closer to breathable, and water is usually present if hard to find.
* Type: Marginal
* Age: 4 - 10 billion years
* Diameter: 10,000 - 15,000 km
* Location: Ecosphere
* Surface: Rocky and barren, little surface water
* Atmosphere: Oxygen / argon, high concentration of carbon dioxide
* Evolution: n.a.
* Life-Forms: Limited to plant life; suitable for humanoid colonization
* Examples: Indri VIII
== Class M ==
Class M planets are typically about the mass of Earth and are in their sun's habitable zone. Their atmospheres contain significant oxygen, liquid water is a significant surface feature, and lifeforms are generally abundant. With more water they would be class N.
* Type: Terrestrial (Minshara Class)
* Age: 3 - 10 billion years
* Diameter: 10,000 - 15,000 km
* Location: Ecosphere
* Surface: Surface water abundant; if water or ice covers more than 80% of surface, planet is considered Class O or Class P
* Atmosphere: Nitrogen, oxygen, trace elements
* Evolution: n.a.
* Life-Forms: Extensive vegetation, animal life, humanoids
* Examples: Earth, Vulcan, Cardassia Prime
* Notes: Class M planets can vary widely in color, cloud cover, and overall appearance. Most Class M planets are characterized by a relatively thin, techtonically active crust floating on a molten rock mantle, which in turn surrounds a liquid metal outer core and a solid inner core composed of metal crystals.
== Class N ==
Class N planets are typically of about the mass of Earth and are in their sun's habitable zone. Due to the greenhouse effect of dense atmospheres heavy in carbon dioxide, their surfaces are very hot and water is found in vapor form, if present at all.
* Type: Reducing
* Age: 3 - 10 billion years
* Diameter: 10,000 - 15,000 km
* Location: Ecosphere
* Surface: High surface temperature due to greenhouse effect; water exists only as vapor
* Atmosphere: Extremely dense, carbon dioxide and sulfides
* Evolution: n.a.
* Life-Forms: Unknown
* Examples: Venus
== Class O ==
Class O planets are typically about the mass of the Earth and are in their sun's habitable zone. Their atmospheres contain significant oxygen, liquid water covers over 80 percent of the surface. Lifeforms are generally abundant. With less water they would be Class M.
* Type: Pelagic
* Age: 3 - 10 billion years
* Diameter: 10,000 - 15,000 km
* Location: Ecosphere
* Surface: Liquid water covers 80% or more of surface area
* Atmosphere: Nitrogen, oxygen, trace elements
* Evolution: n.a.
* Life-Forms: Aquatic vegetation, animal life, humanoids
* Examples: Argo
== Class P ==
Class P planets are typically about the mass of the Earth and are in their sun's habitable zone. Their atmospheres contain significant oxygen, water ice covers over 80 percent of the surface. Lifeforms are generally rare, but resilient. With a higher temperature they could be Class M or O.
* Type: Glaciated
* Age: 3 - 10 billion years
* Diameter: 10,000 - 15,000 km
* Location: Ecosphere
* Surface: Water ice covers 80% or more of surface area
* Atmosphere: Nitrogen, oxygen, trace elements
* Evolution: n.a.
* Life-Forms: Hardy vegetation, animal life, humanoids
* Examples: Exo III
== Class Q ==
* Type: Variable
* Age: 2 - 10 billion years
* Diameter: 4,000 - 15,000 km
* Location: Hot Zone / Ecosphere / Cold Zone
* Surface: Ranges from molten to water and/or carbon dioxide ice, due to eccentric orbit or variable output of star
* Atmosphere: Ranges from tenuous to very dense
* Evolution: n.a.
* Life-Forms: Unknown
* Examples: Genesis Planet
== Class R ==
* Type: Rogue
* Age: 2 - 10 billion years
* Diameter: 4,000 - 15,000 km
* Location: Interstellar space, cometary halos
* Surface: May be temperate due to geothermal venting
* Atmosphere: Primarily volcanic outgassing
* Evolution: n.a.
* Life-Forms: Non-photosynthetic plants, animal life
* Examples: Dakala
== Class S-T ==
Class S and T planets (Gas Ultragiants) are very large, typically 10,000 times the mass of Earth, and are in their sun's cold zone. Low solar radiation and high gravity have allowed them to keep thick atmospheres of hydrogen and hydrogen compounds. High core temperatures cause them to radiate visible light. These are the largest possible planets, as more massive bodies generate enough core heat to initiate fusion reactions and become stars.
* Type: Ultragiant
* Age: 2 - 10 billion years
* Diameter: 10 - 50 million km (Class S); 50 - 120 million km (Class T)
* Location: Cold Zone
* Surface: Tenuous, composed of gaseous hydrogen and hydrogen compounds; radiates considerable heat
* Atmosphere: Zones vary in temperature, pressure and composition; water vapor may be present
* Evolution: n.a.
* Life-Forms: Unknown
* Examples: Unknown
== Class Y ==
Class Y planets (Demon Class) are typically about the mass of earth and are in their sun's habitable zone. Their gravities are about Earth's. Their atmospheres are full of toxic gases, radiation, etc. Their atmospheres release spikes of thermeonic (ther-me-on-ick) radiation. The temperature on the planet is over 500 degrees Kelvin.
* Type: Demon
* Age: 2 - 10 billion years
* Diameter: 10,000 - 50,000 km
* Location: Hot Zone / Ecosphere / Cold Zone
* Surface: Temperature can exceed 500ºK
* Atmosphere: Turbulent, saturated with toxic chemicals and thermionic radiation
* Evolution: n.a.
* Life-Forms: Mimetic (Delta Quadrant)
* Examples: "Class-Y Planet" in Delta Quadrant
* Notes: Classes X, Y, and Z are reserved for planets with environments particularly hostile to humanoid life.