Non-Oxygen Species
v3.0 introduces new species types that breathe methane, ammonia and sulphur dioxide. There is an option on the game window to enable/disable these new species types from appearing.
Each species type has its own set of dangerous gases, so all of the new types have oxygen as a dangerous gas, but none of them have hydrogen for example. Each of the four breathable gases is dangerous to species that breathe the other three.
The requirement for a 20% hydrosphere will only apply to oxygen breathers. Methane breathers simply ignore it, while water is actively dangerous for ammonia and sulphur dioxide breathers, particularly for the latter, due to the reaction between water and the two gases. While Aurora is not a chemistry simulator, it is still worth including this factor as part of colony cost for those species.
Water Ice
0 for Ammonia
0.05 per Hydrosphere % for Sulphur Dioxide. (so 40% = 2)
Liquid Water Present
0.1 per % for Ammonia (so 40% = 4)
1.0 per % for Sulphur Dioxide
Water Vapour (Dangerous Gas)
2.0 for Ammonia
3.0 for Sulphur Dioxide
While the new species types don’t need water, they do require an equivalent. However, tracking four different water-equivalents would over-complicate the situation. Instead, I am restricting the habitable temperature for their potential home worlds to a range where the gas they breathe can also be a liquid. This simplifies the problem and limits the potential habitable worlds. That range depends on pressure, with higher pressure worlds having a greater potential temperature range. Methane is least affected by pressure with sulphur dioxide affected most.
For anyone interested in the formula, it is:
1.0 / (1.0 / Boiling Point Kelvin - 8.314 * logarithm(Pressure / Enthalpy Vaporisation);
That results in the following effects.
The formula above is used only for determining whether a planet or moon is suitable as a home world. Once a species is generated, their breathable gas pressure, temperature range and maximum atmospheric pressure is set in the same way as an oxygen-breather, based on a range from their starting values, which is in turn based on the environment of their home world. This approach limits potential home worlds in a realistic way, without complicating colonisation or tracking water-equivalents.
EDIT: After testing, I have added a minimum breathable range of gas freezing point + 40K for Methane, 60K for Ammonia and 120K for Sulphur Dioxide. The range can still be greater at higher pressure, but allows a greater chance of generating a home world at lower pressures.
Once generated, the only mechanical difference between the new species types and the oxygen-breathers is the type of gas they breath, the gases they treat as dangerous and their relationship to water. Everything else functions in the same way (gravity, temperature, pressure), although the range of numbers involved is likely to be different due to their very different starting points.
Infrastructure works in the same way for all species and is interchangeable (except that different species may require different amounts for the same planet - as they do now).
Currently (in v2.7.1), when NPRs are generated at game start, the game generates and discards systems until it finds one with a planet suitable as home world. This process now includes checks for planets suitable for methane, ammonia and sulphur dioxide breathers. Similarly, as new systems are generated after game start, each planet is checked as a potential home world for each species type. Additional systems generated for multi-system NPRs will check for colony sites appropriate to the species requirements.
After game start, the AI will take account of all of the above changes when considering colony sites, planetary and system value and terraforming requirements.
It is not straightforward to determine exactly how many additional races will be generated due to the complex nature of system generation. Testing so far suggests that on average there will be a similar number of oxygen and methane races at game start, with SO2 and Ammonia appearing about half as often. This may change as I modify some of the generation parameters after further testing.
This means that overall, there may be three times more races generated during exploration. Generation now is very low so that should be fine.