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Planetary Class Description

O2/H2O Ecology Planetary Classes 

Human habitable world classes are based on a survey point system.  Basic categories such as atmospheric composition, temperature ranges, life form characteristics, radiation levels and other factors receive points as they deviate from conditions favorable to unprotected Human survival.  The classification is based on the sum of all computed adverse factors and then graded into planetary classes A-H.  These classes comprise the Simple Nomenclature for planetary classification.



Near Terran norm.  Compatible, edible life forms containing all essential nutrients.  Habitable without technological assistance over most areas of the planet.
B Very near Terran norm.  Mostly habitable without technological assistance.
C Suitable for human habitation.  Large areas habitable without technological assistance.
D Acceptable for human habitation.  Some areas habitable without technological assistance.  Minimal life support requirements over most areas.
E Marginally acceptable for human habitation.  Minimal technological assistance required to sustain human life in many areas.
F Not suitable for human habitation.  Minimal or moderate technological assistance required over most areas of the surface.
G Not habitable.  Moderate or full technological assistance required over most or all surface areas.
H Hostile to human habitation.  Full technological assistance required over all surface areas.

Human habitable worlds are also expressed in Detailed Nomenclature X:Y:n:m where the first designation (X) is H for Habitable or Human, the subclass designation (Y) is the simple habitability class of A-H, the tertiary designation (n) is the dominate life type classification, as described below, and the final designation (m) indicates life complexity, also described below.

Life Class
0 DNA I with fully compatible amino acids and nutrients essential for Human life
1 DNA I missing some amino acids or nutrients essential for Human life
2 DNA II: Incompatible with Human nutrition
3 DNA III: Poisonous to Human life
4 SNA I: Incompatible life structure
5 SNA II: Incompatible life structure
6 Silicon I: Silicon-based life structure
7 Silicon II: Silicon-based life structure
8 PNA:  Incompatible life structure
9 Other: Rare or unclassified life structure
Terran Example
0 No life present or past Hadean Eon
1 Anaerobic simple prokaryote life Archean Eon
2 Aerobic prokaryote life Early Paleoproterozoic Era
3 Single celled eukaryote life Late Paleoproterozoic Era
4 Simple metazoan life Ediacaran Period
5 Diverse metazoan life Cambrian Period
6 Complex metazoan life Devonian Period
7 Intelligent metazoan life Human Period
8 Extinct intelligent life Post Human Period
9 Dead world.  All former life extinct Post Runaway Greenhouse


Non-Human Habitable Planetary Classes

Non-Human habitable worlds follow a similar nomenclature to habitable worlds, with the Simple Nomenclature often sufficient to characterize the planet.  A non-inclusive listing of secondary designations is noted within the primary class description below.  Tertiary and quaternary designations are only expressed for living worlds and correspond to Human habitable designation values.



Regional classification for Icy planetary belts similar to the Solar Kuiper region.  This is a belt classification and individual bodies within this belt may be of Class T or Z (and rarely N), dependent on size.


Jovian planet.  This classification covers all "Gas Giant" planets from 4 to 4000+ Terran masses (the deuterium burning limit), with a predominately hydrogen-helium atmosphere and no accessible planetary surface.   Subclasses 1-9 describe ice (1-3), gas (4-6) and hot (7-9) giants of under 40 masses (1,4,7), 40-400 masses(2,5,8) and over 400 masses (3,6,9).


Chlorine/water or chlorine/ammonia ecosphere planets.  Several subclasses exist, including K:1, Khzraut-compatible warm water cycle ecologies, K:2 cold water cycle and K:3, ammonium cycle ecologies. 


Not used


Mars type cold thin carbon dioxide-based atmosphere planets.  These planets have atmospheric pressures below .2 bar and little or no liquid water.  Subclasses M:0-9 are based on density classifications identical to those of class T.


Planets with primarily nitrogen atmospheres and no free oxygen.  Subclasses include N:1, nitrogen/carbon dioxide/ liquid water worlds similar to early Terra, N:2 cold nitrogen/methane worlds similar to Titan and N:3 cold nitrogen/ethane worlds similar to Stygia.


Not used: proposed for use with proposed large Orbital artificial structures.


Regional classification for rocky Planetoid belts similar to the Solar Asteroid belt region.  This is a belt classification and individual bodies within this belt may be of class T or Z (and rarely M, N or W), dependent on size.


Brown dwarfs and other Quasi-stellar objects of between 13 and 80 Jupiter masses, regardless of formation method.


Regional classification for Rocky planetoid belts dominated by a number of large planetoid bodies, such as the minor world belt at Delta Pavonis.  This is a belt classification and individual bodies within this belt may be of class T or Z (and rarely M, N or W), dependent on size.


Sub-jovian planets with predominately hydrogen/helium atmospheres and less than 4 Terran masses.  Subclasses include S:0 sterile worlds, S:1 Alimeen ecosystem and S:2, Adornan ecosystem worlds.


Terrestrial planets with atmosphere of less than .001 bar and mass of at least .001 Terran.  These worlds generally have radii above 1000 kilometers.  Subclasses are computed from the rounded value of the density of the body in cm/g3 and can range from 0 to 9, though values outside the range 1-5 are rare.


Life bearing planets with a nitrogen/methane liquid water cycle ecology.  Subclasses include U:1, Un'aa'graum ideal, and U:2 Zreem ecosystems.


Venus type planets with dense carbon dioxide atmospheres of more than 2 bars density.  Subclasses include V:1 planets of 2-10 bars atmosphere and high/moderate surface temperatures, V:2 planets of 10-100 bars atmospheres and hot surface temperatures and V:3 planets of more than 100 bar atmospheres and hot/molten surfaces.


Planets with moderately dense, primarily carbon dioxide atmospheres of .2 to 2 bar density.  Subclasses include W:0, small worlds retaining carbon dioxide, but not liquid water and W:1, proto-Martian worlds like Vulcan.


Not used for natural bodies: Reserved for artificial structures such as stations, habitats and drifts.


Young primordial worlds of varying atmospheres from the initial planetary formation era comprising a timeframe from solar nebula collapse to the end of early planetary bombardment and radiational differentiation at age 500 million to 1 billion years.  Subclasses 1-9 describe various atmospheric compositions and conditions.


Small solid bodies of at least 10-5 and no more than 10-3 Terran masses.  These bodies are spherical and generally 250-1000 kilometers radius, including large planetoids and moderate sized moons.  Subclasses Z:0-9 are based on density classifications identical to those of class T.  Class Z planets are often called minor planets; smaller bodies are not classified as planets.

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