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PostPosted: Fri Mar 25, 2022 3:57 pm 
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OK, after a long hiatus, I am back and thinking about world generation again. In a previous post, I discussed extending the SIZ code above 10 (A) to account for panthalassic worlds, up to the transition into Gas Giants.

The Traveller ATM code was specifically designed for habitable/mainworlds. I would like to discuss what codes make sense if expanding to NON-mainworlds.

Here is where I fall right now:
CODE
0 - Vacuum (Mercury, Luna etc.)
1 - Trace
2 - Very Thin, Trace - I actually think this should just be Thin, Corrosive - NO oxygen and something that will eat your skin like Chlorine or Sulphur
3 - Very Thin - Another I think should NOT be breathable, Thin, Exotic - No oxygen (Mars), but relatively benign (CO2 or N2 gasses most likely)
4-9 - Thin, Standard, Tainted, Dense as normal
A - Exotic - I would classify this as Exotic, Standard (meaning 0.5-2.0 Atmospheres-ish)
B - Corrosive - Again, Corrosive, Standard
C - Insidious - No real pressure here, just very nasty
D - Very Dense - IF its breathable it should be 8 or 9. This is non-breathable, 2 atmospheres or denser; Very Dense, Exotic.
E - Thin-Low - Such crap, if its like this it should be 4 or 5. This should also be non-breathable; Very Dense, Corrosive
F - Unusual - I kind of like this one, more likely on worlds with elliptical orbits where composition and/or pressure changes over a relatively short period (months or a few years at most).

SO - for Mainworlds, you keep the standard 2D-7+SIZ roll but with the newer definitions that classify ATM 4-9 ONLY as having Oxygen present. ATM 4 and 9 are now much less habitable as they incorporate several of the more extreme versions of pressure and partial-pressure of oxygen.

For NON-Mainworlds, you make the same roll but us a different table to determine atmosphere. Basically, you replace the 4-9 rolls with additional 2, 3, A, B, C, D, and E rolls. I would use separate entries for INNER, MIDDLE, and OUTER zones. So for non-mainworlds, your roll is not the ATM like it is for the mainworld, but at the end, your UWP code still means the same thing.

Still working on the non-mainworld tables, but does this make sense? I realize the canonistas will scream over the definition changes, but honestly, this isn't Star Trek with asteroids with breathable atmospheres, so the codes that represent breathable atmospheres should reflect that. These changes also more closely match the Trade Codes. It made no sense to me that ATM 4 could be Agricultural, but not ATM D or E...

If I was doing a REALLY hard science setting, I would drop 4 and 9 from having oxygen, make 5 "Thin" which implied too low of oxygen to breath without a respirator. 8 would basically be Very Dense, Tainted requiring a diluter to function at lower altitudes, but I think that would cause too much change...

What do you think? Reasonable tweaks to definitions yet still allowing expansion of the rules to non-mainworlds and non-habitable zone worlds?

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PostPosted: Fri Mar 25, 2022 4:24 pm 
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My worldgen can generate worlds in the inner, habitable, middle or outer zones (see viewtopic.php?f=30&t=3197 ) - atmospheres outside the habitable zone can't be breathable.

(looks like you made a duplicate post when you posted this, so I deleted the other one).

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PostPosted: Fri Mar 25, 2022 7:14 pm 
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Sorry about that. I was thinking that the Middle Zone would be an expanded version of the Habitable Zone. Extending from the Vaporline (if such a thing exists - its the line where water and other volatiles evaporate and can't be liquid on the surface) and the Snowline (where those same volatiles are solid and can't exist on the surface). The Habitable zone is somewhere in the that zone where under normal atmospheric conditions, liquid water can exist on the surface.

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PostPosted: Fri Mar 25, 2022 10:06 pm 
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The Middle Zone is the region between the outer edge of the Habitable zone and the inner edge of the Outer zone (the Frost/Snow Line). The inner edge of the outer zone is defined by the line beyond which the blackbody temperature is below the temperature at which most volatiles freeze (I set that at 175K, which seemed to match most calculated figures). The habitable zone width is somewhat arbitrary as it depends on the planet's environment, but it's usually assumed to be 0.9-1.2*SQRT(Luminosity).

At least that's how I defined it in my worldgen.


I dunno if I posted this anywhere but these are the notes I had for my atmospheric definitions:

Quote:
0: Vacuum/Trace. The planet has no atmosphere at all, or the barest trace of one.
Pressure range: 0 to 1 millibar (1000 microbars).
Location: Any
Examples: Luna, Mercury, Europa, Ganymede, Triton.


1: Tenuous: Tenuous atmospheres ary extremely thin, but can still be sufficiently thick to generate significant weather and erosion. They will be composed primarily of either nitrogen or carbon dioxide, with traces of ammonia, methane or noble gases, but oxygen is never present beyond trace amounts generated by photolysis or radiolysis of inorganic compounds. Note that these are technically a subclass of Exotic atmospheres, but are separated since they are commonly found on less massive worlds.
Pressure range: 1 to 99 millibars (0.001 to 0.099 atmospheres).
Location: Any
Composition: Any (no oxygen)
Example: Mars.


2: Very Thin, Tainted: These atmospheres are only found in the habitable zone, and contain a tainted N2/O2 mix. In all cases, there is a Low O2 taint, which means the atmosphere is unbreathable without a compressor. There is also a chemical or biological taint in the air that requires a filter mask. The pressure is at best equivalent to the top of Mount Everest on Earth.
Pressure range: 0.1 to 0.4 atms.
Location: Habitable Zone
Composition: Tainted N2/O2
Example: none in Solar System.


3: Very Thin: These atmospheres consist of an N2/O2 mix. However, the pressure is at best equivalent to the top of Mount Everest on Earth, which makes the air unbreathable without a compressor. A Low O2 taint is in effect (though in this case the atmosphere does not count as “tainted”), but there are no chemical or biological taints to deal with.
Pressure range: 0.1 to 0.4 atms.
Location: Habitable Zone
Composition: N2/O2
Example: (top of Mt. Everest on Earth)


5/6/8: Breathable Atmospheres (Thin/Standard/Dense). Worlds with Breathable Atmospheres are are always N2/O2 mixes, with Oxygen Pressure between 0.1 and 0.5 (see box).

These worlds are by definition located either in the habitable zone of a star system or not very far inside or outside it. The only way that a breathable atmosphere can be found outside the habitable zone is through terraforming, unusual albedo/greenhouse effect combinations that make the world habitable. Alternatively, the star’s habitable zone may have expanded through stellar aging, leaving a formerly habitable world inside or creating a new one beyond the former habitable zone. Usually such a world will be located within an AU of the borders of the habitable zone.
Pressure range: 0.4 to 2.5 atms.
Location: Habitable Zone
Composition: N2/O2
Example: Earth.


Quote:
Breathable Atmospheres

For an atmosphere to be ‘Breathable’ it must contain enough oxygen for humans to breathe without technological help (i.e. oxygen tanks, rebreathers, and compressors). This is denoted by by the “O2 ATA” (ATA = Atmosperes Absolute), sometimes referred to as the “Oxygen Pressure”. This is determined by multiplying the atmospheric pressure at sea level (in atms) by the fraction of oxygen in the atmosphere. Thus, a world with a dense atmosphere at 2 atms pressure and 19% O2 will have an Oxygen Pressure of (2 x 0.19 =) 0.38.

For an unmodified human acclimatised to sea level pressure on 21st century Earth, “safely breathable” is considered to be between 0.195 and 0.235 O2 ATA. It is possible - with lengthy acclimatisation and over several generations of living at high altitudes - to survive at O2 ATA as low as 0.10, but long-term physiological effects from low oxygen may become apparent even in those adapted to the gas mix, including an increased chance of miscarriage, exhaustion or dizziness, and shortened lifespan.

An O2 ATA above 0.235 is also dangerous, but can be tolerated for longer periods. High oxygen levels of greater than 1.4 ATA will result in neurological damage (convulsions and seizures) and death. Below this level, however, there is a wide range of oxygen ATAs at which O2 acts like a poison, slowly destroying and damaging lungs and soft tissue. Lung and tissue damage can occur at prolonged oxygen levels of above 0.5 ATA. Higher oxygen pressures (e.g. in hyperbaric pressure chambers or for medical purposes) can be tolerated for short periods but even 24 hours exposure at 0.75 ATA will result in pulmonary damage. We will therefore assume that the upper level of oxygen pressure for longterm human habitability is 0.5 O2 ATA.

An O2 ATA between 0.10 and 0.50 qualifies an atmosphere as ‘Breathable’ without assistance or protective measures (though acclimatisation will be necessary at the extremes). If the O2 ATA is outside this range, then the atmosphere is considered Tainted - it is either a Low O2 Taint or a High O2 Taint. The actual upper limit of oxygen in an atmosphere is not clear - at some level, there will be so much oxygen in the atmosphere that it becomes likely that everything flammable would be igniting or oxidizing on the planet’s surface, which would bring the O2 percentage down anyway. Assume that irrespective of pressure, an atmosphere cannot contain more than 40% Oxygen as a proportion of the total gas content.

Since Thin atmospheres have lower pressure, they are more likely to have a Low O2 taint - similarly, Dense atmospheres have higher pressure and are therefore more likely to have a High O2 taint than standard atmospheres. Habitable atmospheres with Very Thin pressures automatically have the Low O2 taint, and Habitable atmospheres with Very Dense pressures automatically have the High O2 taint - this is regardless of whether they contain other taints.

A “Garden” world is defined as a world with a Thin, Standard, or Dense Habitable atmosphere that has no high or low O2 taint and no chemical or biological taints. These are breathable by humans without the need for any protective measures.



2/4/7/9: Tainted Atmospheres.
Tainted atmospheres are N2/O2 mixes with some component that renders them unbreathable without assistance. There are four types of taint - Low O2, Chemical Taint, Biological Taint, and High O2. The first and last are not, strictly speaking, ‘taints” but are rather a property of the atmosphere itself that renders it unbreathable.

“Low O2” means that the O2 ATA (see “Breathable Atmospheres” box) is too low for any human to breathe unaided for an extended period - acclimatisation is not possible. It may be possible for humans already acclimatised to Thin Garden atmospheres with low O2 ATA to breathe Low O2 atmospheres for a brief period, but in most cases some assistance is required for extended periods or oxygen asphyxia will result.

“Chemical Taint” means that the N2/O2 atmosphere contains a chemical that is damaging to humans. For example, it may contain a large amount of CO2, or sulphur compounds, or biologically generated chlorine. Some protective measures (which may range from a simple filter mask to a full body suit, depending on the severity of the taint) are required to avoid being harmed by the chemicals in the atmosphere. It is generally not possible to biologically adapt to Chemical Taints, at least without significant genetic engineering.

“Biological Taint” means that the N2/O2 contains a biological taint that is damaging to non-native humans. For example, it may contain harmful bacteria, spores, pollen, or dangerous diseases. Again, the protection required varies depending on the severity of the taint - pollen that irritates on ingestion would require a simple filter mask, but airborne diseases absorbed through the skin would require a full body suit. Biological taints *can* be biologically adapted to - either naturally or via genetic engineering - so it is possible that natives would become immune to the taint. Visitors on the other hand must adopt protective measures or succumb to the effects of the taint.

“High O2” means that the O2 ATA (see “Breathable Atmospheres” box) is too high for any human to breathe unaided for an extended period - acclimatisation is not possible. It may be possible for humans already acclimatised to Dense Garden atmospheres with high O2 ATA to breathe High O2 atmospheres for a brief period, but some assistance is required for extended periods or hyperbaric oxygen toxicity will result.

Pressure range: 0.4 to 2.5 atms.
Location: Habitable Zone.
Composition: N2/O2 with taint.
Example: None in the solar system.


A: Exotic: These are atmospheres that contain no free oxygen, and are the most common in the universe. Their main consituents are usually CO2 or N2, with small amounts of CH4 or NH3 - active chemical components may be present but are non-irritant, which means that they not significantly damaging on exposure. The lack of oxygen means that protective measures are always required to allow humans to survive on the surface and exposure to the atmosphere will be fatal - ambient temperature and pressure may require additional protection. Exotic atmospheres can be found anywhere in the system - these atmospheres are usually found in the habitable zone around “Pre-Garden” worlds that have anaerobic life that have not yet produced free oxygen.
Hydrographics on worlds with exotic atmospheres may consist of liquid water if located in the habitable zone. Beyond the habitable zone other liquids are possible if the surface conditions allow them to be stable, such as liquid ammonia or liquid ethane. Any atmosphere pressure type from Tenuous to Superdense may be Exotic in composition - though if the pressure is Tenuous the atmosphere is defined as UWP 1, and if the pressure is Superdense then the atmosphere UWP is defined as F instead of A.

Pressure range: 0.1 to 100 atms.
Location: Any orbital zone.
Composition: Any non-irritant mix with no free oxygen.
Example: Early Earth, Titan.


B: Corrosive: These atmospheres contain no free oxygen and also contain a reactive component (usually an acid). As such, they are more hostile environments than Exotic atmospheres. The majority of worlds with Corrosive atmospheres are located within the frost line (mostly in the Inner or Habitable zone) and are therefore hot. The main atmospheric consituents are usually CO2 or N2, with small amounts of HCl, H2SO4, SO2, or Cl. Pressures range from 0.1 to 100 atms. Corrosive atmospheres are usually damaging to organic and inorganic material. The extent and severity of the damage depends largely on the chemistry of the atmosphere as well as ambient temperature and pressure, but tends to be exacerbated in denser atmospheres. Regular maintenance is required to keep environments sealed - again, the timescale depends on local conditions.
Pressure range: 0.1 to 100 atms.
Location: Any orbital zone.
Composition: Any irritant mix with no free oxygen.
Example: Venus.


C: Inferno: The Inferno atmosphere type is a ‘meta-classification’ that replaces the Insidious atmosphere, and is reserved for extremely hostile environments. These environment present frequent, direct and deadly threats to lifeforms, and as such Inferno worlds are usually uninhabited. These atmospheres usually contain no free oxygen. The threat may not necessarily come from the atmosphere itself and is also not necessarily temperature-related either. Examples of Inferno worlds include planets with mostly molten surfaces, very high levels of penetrative radiation, regular major asteroid impacts (e.g. very young worlds), or extremely corrosive atmospheres. Worlds with surface pressures of greater than 100 atms would be classed as Superdense (atm F) worlds instead. If the GM cannot think of a sufficiently extreme environment, replace this with atmosphere B (Corrosive) instead. Inferno environments are not limited to large worlds - they can be assigned to a planet of any size if its circumstances fit this definition. Personal protective measures are usually rendered rapidly ineffective in these environments, and accomodations tend not to last long - the environment is simply too harsh to allow them to survive long.
Pressure range: any.
Location: Any orbital zone.
Composition: Any, with extreme environmental hazards.
Example: Io.


D: Dense, High: These are always N2/O2 mixes, but have surface pressures between 2.5 and 100 atms. They are massive worlds and are characterised by relatively small scale heights that allow the pressure to decrease rapidly with altitude. They are unbreathable at the surface (largely due to the threat of nitrogen narcosis and hyperbaric oxygen toxicity), but may become breathable at high altitudes as the ambient pressure decreases with height. If the surface pressure is very high, the air may only become breathable at altitudes above the highest mountains. These worlds tend to have high densities, and are always located in the Habitable Zone. Similarly to Very Thin atmospheres, a High O2 taint is always in effect on these worlds, though the atmosphere may also be biologically or chemically tainted.
Pressure range: 2.5 to 100 atms.
Location: Habitable Zone.
Composition: N2/O2 mix, possibly chemically or biologically tainted.
Example: None in our solar system.


E: Thin, Low: This replaces the Ellipsoid worlds from the old world generation system - these were unrealistic. Thin, Low atmospheres settle into deep ravines and chasms on the planetary surface, possibly leaving the rest of the planet’s surface exposed to vacuum. These worlds are massive and their surfaces have extensive basins or huge, deep canyon systems (similar in scale to Valles Marineris on Mars) for the atmosphere to settle in. The high planetary mass ensures that the planet’s atmosphere has a small scale height - this means it rapidly decreases in pressure with altitude so that the “highland” regions have local pressures of less than 0.1 atms (technically the “highlands” are likely to be near the mean surface level of the planet).
Pressure range: 0.41 to 0.75 atms (in lowlands), less than 0.1 atms in highlands.
Location: Any orbital zone.
Composition: Any composition.
Example: None in our solar system.


F: Panthalassic: Panthalassic worlds are unusual - they are very large worlds found within the snow line. They migrated inwards from beyond the snow line during the system’s formation, and retain a very large amount of volatile material - they are essentially earth-like bodies with one or more earth masses of liquid water above a rocky core. The upper 100 km or so of the ocean is liquid, the rest is high pressure ice, and the atmosphere is saturated with water vapour. Atmospheric composition is usually N2, O2, H2O and CO2. These are the only worlds with O2 atmospheres that can be found in the Middle Zone - the oxygen forms from the breakdown of water vapour by UV radiation in the saturated atmosphere. They have a strong greenhouse effect and are generally hot (especially in the habitable zone), but high pressure prevents their water from boiling off at the elevated temperatures.
Pressure range: 2.5 to 100 atms.
Location: Habitable or Middle Zone
Composition: N2/O2/H2O/CO2.
Example: None in our solar system.


G: Superdense: Superdense is a specific Atmosphere UWP classification, used for atmospheres with Superdense pressures. Any Superdense (in pressure) atmosphere with Exotic or Corrosive composition is classes with an Atmosphere UWP of G. These atmospheres are extremely thick and dense - the surface pressure is greater than 100 atms, up to 1000 atm. Atmospheric composition is usually CO2, N2 and/or Helium - no free oxygen will be present. If the composition is Inferno, this signifies that H2 is present - in this case the world is a Subgiant (Atmosphere UWP of H).
Pressure range: 125 to 1000 atms.
Location: Any orbital zone
Composition: N2/CO2/He mix, no O2.
Example: None in our solar system.


H: Subgiant: Subgiants straddle the boundary between terestrial worlds and small gas giants - they are largest, most massive worlds with superdense atmospheres that consist largely of hydrogen and helium. Their atmosphere is at least a thousand km thick, with crushing pressures at the surface - the surface pressure is greater than 100 atms, up to 1000 atm. Atmospheric composition is primarily H2 and He with small amounts of other gases - no free oxygen will be present.
Pressure range: 125 to 1000 atms.
Location: Any orbital zone
Composition: H2/He mix, no O2.
Example: None in our solar system.

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