Traveller Tuesday: Planetary Habitability Codes

Are you a Trekkie? Do you wish you had the opportunity to say "Class M planet" in a game of Traveller?  Well, now you can.

By cross-referencing Traveller's Universal World Profile definitions with Star Trek's Planetary Classifcation definitions, we arrive at this handy Venn Intersection of science-fiction geekery.

Please note that these are approximations; Star Trek's system isn't as granular as Traveller's UWP.


Class A, B, C

• Different only in how the planet is heated
• Class A is geothermal (heated internally)
• Class B is geomorteus (heated by a star)
• Class C is geoinactive (frozen)
• Size:1-6
• Atmospheres: 0-3
• Hydrographics: 0-1 

Class D

• Planetoids
• Size:0-1
• Atmospheres: 0
• Hydrographics: 0

Class E, F, G

• Highly volcanic
• Class E is geoplastic: the entire surface is molten
• Class F is geometallic: the surface has cooled somewhat with significant metal deposits
• Class G is geocrystalline: volcanic eruptions have mostly stopped and the surface is beginning to metamorphose into traditional rock
• Size:6-9
• Atmospheres: 9-12
• Hydrographics: any

Class H

• Desert
• Size: 5-9
• Atmospheres: 9-13
• Hydrographics: 0-1

Class I

• Large Gas Giants

Class J

• Small Gas Giants

Class K

• Uninhabitable without technology
• Size: 3-6
• Atmospheres: 0-10, but always tainted or exotic
• Hydrographics: 0-1

Class L

• Marginally habitable
• Size: 6-9
• Atmospheres: 4-9, tainted
• Hydrographics: any

Class M

• Terrestrial
• Size: 6-9
• Atmospheres: 5-9 (taint is likely to be from industrial pollution)
• Hydrographics: any

Class N

• Terrestrial, with reducing (hostile) atmospheres
• Size: 6-9
• Atmospheres: 5-12
• Hydrographics: any

Class O, P

• Water worlds; main difference is that class O is pelagic and class P is glaciated
• Size: 6-9
• Atmospheres: 5-9
• Hydrographics: 8-10

Class Q, R

• a.k.a "questionable" or "random", i.e. "WTF? This makes no sense. I blame the Ancients."
• Size: 3-9
• Atmospheres: 1-10
• Hydrographics: any

Class S, T

• Supermassive Gas Giants 

Class U, V, W (unofficial)

• Artificially constructed habitats
• Class U: hollowed-out asteroid
• Class V: Ringworld
• Class W: Dyson Sphere

Class X, Y, Z 

• a.k.a. "hellworlds" or "demon planets"
• Size: 6-9
• Atmospheres: 10-15
• Hydrographics: any, but rarely H20