Planetary and Stellar classes

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The following information is gathered from various sources, including NASA documents, The original FASA Star Trek RPG, Memory Alpha (where it does not flagrantly disagree with otherwise established classes), and various other sources.

List of known classes

Star Trek Planetary Classes
Class Name of Class Surface Atmosphere Description Life Forms Example
A Geothermal Partially molten, very hot Much volcanic activity, small, barren Carbon Dioxide/Hydrogen None Gothos
B Geomorteus Partially motlen Helium, soduim, thin Molten, unstable surface None Mercury, Nebhilum
C Geoinactive Barren None No geological activity, cold barren surface None Psi 2000
D Dwarf Barren, cratered Thin or none composed of ice, barren, cold None Pluto, Ceres, Eredas-Il
E Geoplastic Molten, High Temperatures Hydrogen compounds Earliest stages of habitable world, geologically active, hot None Excalibia
F Geometallic Volcanic, barren Carbon dioxide, ammonia, methane Early forms of life, water condensation, barren surface Bacteria Janus IV
G Geocrystalline Rocky, mostly barren Carbon dioxide, oxygen, nitrogen Early form of life-sustaining worlds Vegetation, simple organisms Delta Vega
H Desert Little water Oxygen, nitrogen, argon, metals Little rain, less than 20% surface water Drought-resistant plants and animals, possibly humanoids Ocampa, Nimbus III, Tau Cygna V
I Ice Giant Rock, ice, methane, ammonia Hydrogen, helium Planet core is mostly ice, outer fringe of system None Uranus, Neptune
J Gas Giant Liquid metallic hydrogen Hydrogen, helium Maximum wind speeds of 600kph (373mph), liquid and gaseous hydrogen None Jupiter, Saturn
K Adaptable Barren, little surface water Thin, mostly carbon dioxide Suitable for colonization through pressure domes None Mars, Mudd
L Marginal Rocky, little surface water Argon, oxygen, trace elements Rocky, forested worlds, suitable for terraforming Plants, no animals Alarin III, Ciden II, Indri VII
M Terrestrial Between 20-80% surface water, fertile land Nitrogen, oxygen, argon silicate rocks, suitable for humanoid life, fertile land Plants, animals, humanoids Earth, Vulcan, Cardassia
N Reducing Barren, high temperatures carbon dioxide and sulfides High air temperature, density and pressure, up to 500C (932F) None Venus
O Pelagic More than 80% water, archipelagos Nitrogen, oxygen, argon Very warm atmospheres and abundant surface water, tropical Tropical plants, cetacean life, rarely humanoid Delta IV, Bolarus IX, Azati Prime
P Glaciated More than 80% water, frozen Nitrogen, oxygen Frozen worlds, very cold, rarely above freezing Hardy plants, animal life, humanoid Andoria, Exo III, Rura Penthe
Q Variable Molten, frozen, jungle, etc tenuous to dense Deserts and rainforests exist within a few kilometers, glaciers near the equator None Genesis Planet
R Rogue Temperate Primarily volcanic outgassing Forms in a star system, but is expelled. Can maintain habitable areas if geologically active Non-photosynthetic plants, animals Dakala, Beneihm, Founders' Homeworld (prior to 2373)
S Gas Supergiant Liquid metallic hygrogen Hydrogen, helium Similar to Class J Gas Giants with liquid hygrodren cores surrounded by hydrogen and helium atmosphere None Tethe-Alla IV
T Gas Ultragiant Liquid hydrogen, deuterium Hydrogen, helium Category of largest size of planets. Similar to class J and S. If sufficiently massive can possibly ignite into a red dwarf star, causing a binary system None Tethe-Alla V, Diadem
X Chthonian Barren, extremely hot None Failed Class T, stripped of helium/hydrogen atmosphere. Dense, Metal-Rich core None Osirus
Y Demon Barren, extremely hot Turbulent Toxic radiation, extreme temperatures, atmospheric storms with winds up to 500kph (311mph) Mimetic Planet Hell (Delta Quadrant)

Formerly Used Categories

Class Surface Atmosphere Description Example
A tenuous, may not be present reducing; methane, etc. radiates heat, "failed" star Jupiter, Saturn
B tenuous, may not be present reducing non-radiant Neptune
C iron/silicate reducing/dense high surface temperature Venus
D nickel-iron/silicate (A-G)none, (H-N)tenuous asteroids Ceres
E silicate, some metals reducing/oxidizing large molten core Janus IV
F silicate, some metals oxidizing very young Delta Vega
G silicate oxidizing, thin desert planet Rigel XII
H silicate variable geologically active Gothos
I metallic/silicate fluid, very dense small/young Excalibis
J silicate very tenuous, noble gasses moons Luna
K silicate tenuous, some water adaptable with pressure domes Mars
L silicate/water oxidizing geologically inactive Psi 2000
M silicate/water oxidizing geologically active Terra
N water entirely oxidizing pelagic planet Argo
P water/silicate oxidizing glacial planet Breen
R water/silicate negligible Rogue Dakala
S small dense metallic reducing small ultra gas giant Braxis
T small dense nickel-iron reducing large ultra gas giant Luava
Y metallic/silicate reducing demon class Silver Blood planet

Stellar Classes

In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure of the temperature in this chromosphere. Unlike what is the case for planets, stellar bodies are often classed on two scales - size and temperature/color.

Stars based on color and temperature

The following table does include a rough gauge of mass, but this has little to do with the size. Also appended to this is an arabic numeral (0-9), where 0 is among the hottest stars in a class, and 9 is among the coolest.

Class Surface Temperature Color Mass (Solar Masses) Fraction of All Main Sequence Stars
O ≥ 33,000 K Blue ≥ 16 M ~0.00003%
B 10,000–33,000 K Blue/Blue-White 2.1 - 16 M 0.13%
A 7,500–10,000 K White 1.4 - 2.1 M 0.6%
F 6,000–7,500 K Yellowish White 1.04 - 1.4 M 3%
G 5,200–6,000 K Yellow 0.8 - 1.04 M 7.6%
K 3,700–5,200 K Orange 0.45–0.8 M 12.1%
M ≤ 3,700 K Red ≤ 0.5 M 76.45%

The following are called "extended classes", which I think will help us when writing as well.

Class Surface Temperature Color Mass (Solar Masses)
L ≤ 2,000 Red/Brown ≤ 0.08 M
T ≤ 1,200 Brown Dwarf ≤ 0.08 M
Y < 600 K Brown Dwarf ≤ 0.01 M

Other types of stars do exist, and they may be added here at a later date.

Stars based on size

This scale is based on the radius and luminosity effects of a star. They are generally referred to as "luminosity classes"

Class Description
0 Hypergiants
I Supergiants
II Bright Giants
III Normal Giants
IV Subgiants
V Main Sequence Stars
VI Subdwarfs
VII White Dwarfs (Very Rare)

To put things in perspective: Sol is defined as a G2V star. This means it falls into Spectral type G (yellow), is within the hottest 30% of G-type stars (2), and is within the main sequence. To compare, 40 Eridani A (Vulcan's primary sun) is a K1V.