Known Classes for Planets and Atmospheres.
Star Trek's planetary classification system is obviously something that was just thrown together over time, rather like the show itself. Whilst I was Star Trek Role Playing the GM was unable to describe a planet in a nebula, and she wanted to just give it any random letter. I realised then that there are actually certain guidelines to follow to this letter nomenclature.
Planetary Classes near the letter M are generally more likely to support life. The further they are from the letter M, the less likely the planet is to support life, as we know it. Towards the beginning of the alphabet the atmospheres are more tenuous and planet more rocky, towards the end of the alphabet the atmospheres are denser.
The following has been pulled together from various sources including 'The Star Trek Encyclopaedia.' I thought that you might find it interesting, and useful as a resource for fan-fic writing and Role Playing. Feel free to add to it with new classes or descriptions.
I’ve stuck purely to the Canon ‘Classes’, although these two systems are quite inventive (but incompatible with each other) for the missing letters:
http://www.ccdump.org/planetclass.html
http://www.fedsims.com/fsg/library/planets.php
Class 9
Reserved for gas giants.
Out of the 4 gas giants in the Sol system, none are Class 9.
"K'Tal" Class (Klingon designation) (ENT "Sleeping Dogs")
Class D
Regula was a Class-D world. "A few unremarkable ores... a great rock in space" (ST II: TWOK)
Rocky, lack atmosphere or very tenuous, or likely planetary/moon debris that has approached within the Roche limit of another planet. Most likely consisting of the basic silicates from planetary condensation.
Small, rocky planetoids ('The Star Trek Encyclopaedia.')
The ringed Saturn-like world itself, or the asteroid-like objects in its rings? (VOY "Emanations")
Hot, arid, rocky (VOY "Gravity")
Class H
Oxygen/Argon atmosphere (VOY "Scorpion, Part II")
Extremely dry, although sometimes habitable. An example is planet Tau Cygna V (TNG "Ensigns of Command") this established that Class-H worlds could have life forms present in various stages of evolution. They are often desert like and bathed in hyperonic radiation. Hyperonic radiation can be fatal to unadapted humans and possibly accounts for the primitive indigenous life on the worlds.
A class H moon would have been suitable to leave a colony of Borg on, suggesting the Borg are more resilient to these environments than unadapted humans. (VOY "Scorpion, Part II.")
Class J
Gaseous giants, with turbulent atmospheres, in which wind speeds of over 10,000 kilometres per hour are not unknown. Jupiter and Saturn are Class-J planets. (DS9 "Starship Down")
Class K
Unsuitable for humanoid life, even though their gravity fields can fall within M-Class norms.
Adaptable for humanoid use with pressure domes and life-support systems (TOS "I, Mudd")
Class L
A barely inhabitable planet, with a thin atmosphere and extreme temperature.
Cold, "barely habitable" (DS9 "The Ascent")
Generally small, rocky, terrestrial worlds with Oxygen/Argon atmospheres (VOY "The 37's")
"Barely breathable atmosphere" of excess carbon dioxide (DS9 "The Sound of Her Voice")
Class-L planets can sometimes support life, although this is often limited to planet forms. Planet Indri VIII was Class-L (TNG "The Chase")
Class-L worlds have relatively high concentrations of atmospheric Carbon Dioxide, compared to a Class-M planet. Many humanoid species require the use of an Oxygen supplement such as tri-ox compound in order to survive on many Class-L planets. (DS9 "The Sound of Her Voice.")
The oxygen levels vary, some Class L worlds are capable of supporting humanoid life where as others are toxic due to the very high carbon dioxide levels. Water condenses out almost certainly creating seas where primordial life exists as does slightly more developed plantae, monera and fungal forms. Water also flows across the surface of the continental landmasses and a structured water cycle has both developed and settled. Surface plantae can be very developed in some cases with tree life present. It is possible that L is simply a proto-class M world. The worlds support very large oceans and dense atmospheres. Temperatures are generally low.
Class M
Designation for small, rocky terrestrial worlds with Oxygen/nitrogen atmospheres. (TOS "The Cage.") They are highly supportive of life.
"Minshara" Class (Vulcan designation) (ENT "Strange New World")
Class-M atmosphere designation used in TNG.
The worlds are small and made from silicates around denser iron rich cores. They have nitrogen-oxygen-carbon dioxide atmospheres that are modifications of the volcanic out gassing.
A Class-M planet generally has nucleogenic hygroscopic particles in its atmosphere allowing moisture condensation; lack of nucleogenic particles would result in an absence of precipitation and surface water. (VOY "Caretaker.")
Earth and Vulcan are Class-M planets.
The designation Class M is not particularly dependent on the distance from the star as long as the world lies in the designated habitable domains. Both Mars and Venus could have been Class M but due to other factors these are Class-Y and Class-K/L.
Satellites may be classed as M. No Satellite in the Sol system satisfies this criterion, however Class-M moons have been encountered or discussed. One example might be Rinax the satellite of the planet Talax.
Class Y or "Demon" Class
Extremely inhospitable to humanoids. Toxic atmosphere with thermionic radiation; surface temperatures can exceed 500 Kelvin. It can be dangerous for a spaceship even to orbit a Class-Y planet. (VOY "Demon")
"Toxic atmosphere, sulphuric deserts, no trees, no life at all" (VOY "Flesh and Blood")
The atmosphere is dense and contains corrosive compounds. Footprints embedded on the surface remain visible for at least several hours. Probes released from ships incinerate within seconds of entering the atmosphere even shuttles encounter systems failures on landing approaches and normally such procedures are forbidden. Shield modifications have been known to allow shuttle operations within the atmosphere of Y class planets. Surface features suggest tectonic procedures and volcanic vents are common, suggesting degassing on small continuous scales.
A dust residue covers the surface, but given that any volcanism seems more basaltic it would appear that dust is not from explosive discharges but from the vents across the surface. The particulate matter forms hygroscopic particles in the atmosphere and creates a haze with the atmospheric gases. The tectonic processes create monochromatic geological formations of a dull red colour, though browns and even dull golds are not uncommon.
Surface pools contain deuterium, hydrogen sulphate and dichromates. The particular fluid encountered by USS Voyager in 2375 had mimetic properties that reads DNA and recreates it from the protein molecules and possible electromagnetic forces in the silver fluid. The electromagnetic forces are weakened by Nadion bursts.
Star Trek's planetary classification system is obviously something that was just thrown together over time, rather like the show itself. Whilst I was Star Trek Role Playing the GM was unable to describe a planet in a nebula, and she wanted to just give it any random letter. I realised then that there are actually certain guidelines to follow to this letter nomenclature.
Planetary Classes near the letter M are generally more likely to support life. The further they are from the letter M, the less likely the planet is to support life, as we know it. Towards the beginning of the alphabet the atmospheres are more tenuous and planet more rocky, towards the end of the alphabet the atmospheres are denser.
The following has been pulled together from various sources including 'The Star Trek Encyclopaedia.' I thought that you might find it interesting, and useful as a resource for fan-fic writing and Role Playing. Feel free to add to it with new classes or descriptions.
I’ve stuck purely to the Canon ‘Classes’, although these two systems are quite inventive (but incompatible with each other) for the missing letters:
http://www.ccdump.org/planetclass.html
http://www.fedsims.com/fsg/library/planets.php
Class 9
Reserved for gas giants.
Out of the 4 gas giants in the Sol system, none are Class 9.
"K'Tal" Class (Klingon designation) (ENT "Sleeping Dogs")
Class D
Regula was a Class-D world. "A few unremarkable ores... a great rock in space" (ST II: TWOK)
Rocky, lack atmosphere or very tenuous, or likely planetary/moon debris that has approached within the Roche limit of another planet. Most likely consisting of the basic silicates from planetary condensation.
Small, rocky planetoids ('The Star Trek Encyclopaedia.')
The ringed Saturn-like world itself, or the asteroid-like objects in its rings? (VOY "Emanations")
Hot, arid, rocky (VOY "Gravity")
Class H
Oxygen/Argon atmosphere (VOY "Scorpion, Part II")
Extremely dry, although sometimes habitable. An example is planet Tau Cygna V (TNG "Ensigns of Command") this established that Class-H worlds could have life forms present in various stages of evolution. They are often desert like and bathed in hyperonic radiation. Hyperonic radiation can be fatal to unadapted humans and possibly accounts for the primitive indigenous life on the worlds.
A class H moon would have been suitable to leave a colony of Borg on, suggesting the Borg are more resilient to these environments than unadapted humans. (VOY "Scorpion, Part II.")
Class J
Gaseous giants, with turbulent atmospheres, in which wind speeds of over 10,000 kilometres per hour are not unknown. Jupiter and Saturn are Class-J planets. (DS9 "Starship Down")
Class K
Unsuitable for humanoid life, even though their gravity fields can fall within M-Class norms.
Adaptable for humanoid use with pressure domes and life-support systems (TOS "I, Mudd")
Class L
A barely inhabitable planet, with a thin atmosphere and extreme temperature.
Cold, "barely habitable" (DS9 "The Ascent")
Generally small, rocky, terrestrial worlds with Oxygen/Argon atmospheres (VOY "The 37's")
"Barely breathable atmosphere" of excess carbon dioxide (DS9 "The Sound of Her Voice")
Class-L planets can sometimes support life, although this is often limited to planet forms. Planet Indri VIII was Class-L (TNG "The Chase")
Class-L worlds have relatively high concentrations of atmospheric Carbon Dioxide, compared to a Class-M planet. Many humanoid species require the use of an Oxygen supplement such as tri-ox compound in order to survive on many Class-L planets. (DS9 "The Sound of Her Voice.")
The oxygen levels vary, some Class L worlds are capable of supporting humanoid life where as others are toxic due to the very high carbon dioxide levels. Water condenses out almost certainly creating seas where primordial life exists as does slightly more developed plantae, monera and fungal forms. Water also flows across the surface of the continental landmasses and a structured water cycle has both developed and settled. Surface plantae can be very developed in some cases with tree life present. It is possible that L is simply a proto-class M world. The worlds support very large oceans and dense atmospheres. Temperatures are generally low.
Class M
Designation for small, rocky terrestrial worlds with Oxygen/nitrogen atmospheres. (TOS "The Cage.") They are highly supportive of life.
"Minshara" Class (Vulcan designation) (ENT "Strange New World")
Class-M atmosphere designation used in TNG.
The worlds are small and made from silicates around denser iron rich cores. They have nitrogen-oxygen-carbon dioxide atmospheres that are modifications of the volcanic out gassing.
A Class-M planet generally has nucleogenic hygroscopic particles in its atmosphere allowing moisture condensation; lack of nucleogenic particles would result in an absence of precipitation and surface water. (VOY "Caretaker.")
Earth and Vulcan are Class-M planets.
The designation Class M is not particularly dependent on the distance from the star as long as the world lies in the designated habitable domains. Both Mars and Venus could have been Class M but due to other factors these are Class-Y and Class-K/L.
Satellites may be classed as M. No Satellite in the Sol system satisfies this criterion, however Class-M moons have been encountered or discussed. One example might be Rinax the satellite of the planet Talax.
Class Y or "Demon" Class
Extremely inhospitable to humanoids. Toxic atmosphere with thermionic radiation; surface temperatures can exceed 500 Kelvin. It can be dangerous for a spaceship even to orbit a Class-Y planet. (VOY "Demon")
"Toxic atmosphere, sulphuric deserts, no trees, no life at all" (VOY "Flesh and Blood")
The atmosphere is dense and contains corrosive compounds. Footprints embedded on the surface remain visible for at least several hours. Probes released from ships incinerate within seconds of entering the atmosphere even shuttles encounter systems failures on landing approaches and normally such procedures are forbidden. Shield modifications have been known to allow shuttle operations within the atmosphere of Y class planets. Surface features suggest tectonic procedures and volcanic vents are common, suggesting degassing on small continuous scales.
A dust residue covers the surface, but given that any volcanism seems more basaltic it would appear that dust is not from explosive discharges but from the vents across the surface. The particulate matter forms hygroscopic particles in the atmosphere and creates a haze with the atmospheric gases. The tectonic processes create monochromatic geological formations of a dull red colour, though browns and even dull golds are not uncommon.
Surface pools contain deuterium, hydrogen sulphate and dichromates. The particular fluid encountered by USS Voyager in 2375 had mimetic properties that reads DNA and recreates it from the protein molecules and possible electromagnetic forces in the silver fluid. The electromagnetic forces are weakened by Nadion bursts.
