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 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
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
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
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.
NOTE:All information above is taken from Geoffrey Mandel's "Star Trek Star Charts: The Complete Atlas of Star Trek" available from Pocket Books.
