Moon AtmospheresAssigning an atmosphere to a moon is straightforward, but the simulation of e.g. a gas giant moon might need to simulate atmosphere and transport on the gas giant as well if the effect of indirect radiation is to be considered.Thus, an atmosphere_basic block can occur twice - if it occurs before the moon block has been started, the parser assumes it refers to the planet, if it occurs after the parser assigns the definition to the moon. The same is true for a hydrosphere_basic block. As the detailed atmosphere composition is not needed to simulate IR absorption or transport, there can be only one atmosphere block - if there is only a planet defined, it is assumed to refer to the planet, if a moon is defined it is assumed to refer to the moon. The same is true for a possible weather block - that too refers to the actively simulated world - which is the moon if declared. Thus, if you need to simulate a planetary atmosphere to fix the transport coefficients for the mother planet of the moon, you first need to run the simulation without the moon, get all the needed coefficients, pack them into an atmosphere_basic block and put that before the eventual moon definition comes in.
Ran, Gymir and FenyaThe config file example25.cfg gives the example of a gas giant moon - the gas giant Gymir orbits the hot star Ran and is in turn orbited by the moon Fenya (in the fictional setting it is taken from it is orbited by two major moons, Menya and Fenya - we will meet Menya in the next part of the series).Fenya is a dry, Mars-like world with a tenuous CO2 atmosphere:
and as the config file contains a moon definition, the atmosphere is automatically assigned to Fenya. Running the simulation provides the parameters for the transport as
and these are accordingly put in an atmosphere_basic block following the moon declaration.
Conditions on FenyaTemperatures on Fenya are a chilly 260 K maximum, ranging to 180 K in the polar regions as the thin atmosphere is not overly efficient to transport heat and the maximal irradiation is only 470 W/m2.
Fenya is tidally locked, and so Gymir frequently eclipses Ran on the Gymir-facing side which ends up as a coolor spot on the surface. There is nothing in the dynamics of the moon which we wouldn't have seen in earlier sections - but the world serves as a nice illustration how important the atmosphere is, as its sister moon Menya has practically the same orbital and irradiation conditions and only a different atmosphere - and ends up being radically different.
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