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Forum » SpaceEngine » General Discussions » Finding Molar Mass? (Just another thought)
Finding Molar Mass?
HanakofuroshiraDate: Monday, 08.08.2016, 19:40 | Message # 1
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https://www.reddit.com/r....physics

In this link, there is a person analyzing the molar mass of Kerbin. The OP posted an equation,
M=(ρRT)/(P) where M is molar mass, ρ is density, R is the ideal gas constant, T is temperature, and P is pressure. This only apparently works for an ideal gas.

Is it possible to accurately determine the molar mass of any atmosphere, and/or even possibly the rocky part of a planet(sans fluid giants)? Now, we could obviously take the percentages of the atmospheric makeup since we currently have those in Space Engine to produce a molar mass, but there's currently no information on rocky composition yet.

BTW, we must congratulate SpaceEngineer on a good job for 0.98! My computer finally decided to download it this morning, and I've been enjoying the planemo.





Fluent in music, math, Solresol, and hopefully someday, astronomy.

Edited by Hanakofuroshira - Monday, 08.08.2016, 19:45
 
WatsisnameDate: Monday, 08.08.2016, 20:18 | Message # 2
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Quote Hanakofuroshira ()
This only apparently works for an ideal gas.


Yep, this is the correct formula, and is derived through the ideal gas law. It works for most planetary atmospheres you are likely to find -- the law breaks down when the molecules are very large or near phase transitions (like liquid or superfluids).

The average molar mass of a solid planet is much harder to find without knowing the composition first.

Dividing the volume of the planet by its mass (edit: how about the other way around, silly me) gives you its density, but then going from density to molar mass is not straightforward. There are multiple compositions that could produce it, and it further depends on the extent to which the planet is compacted by its own gravity.

We could instead use the mass-radius relationship for solid planets, determining the bulk composition from the planet's mass and radius together, and then breaking that down to average molar mass. But this is only approximate, since the mass-radius relationship is not a very sensitive measure of composition.





 
HanakofuroshiraDate: Monday, 08.08.2016, 23:08 | Message # 3
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You see, I did consider what you mentioned about the density of planets before I created this thread, but I thought it was rather vague in trying to determine a molar mass. I know that determining molar mass is impossible without knowing composition, but there should still be a vague way if we estimate planetary composition and use it in tandem with the mean density.

There's apparently a list of the elements currently being used for atmospheric compositions within the .cfg files, but I haven't been able to find them, and nobody has given me deep insight on the probability parameters that are used when the engine generates planets. I can't wait until we get planetary composition for rocky planets! ok





Fluent in music, math, Solresol, and hopefully someday, astronomy.
 
Forum » SpaceEngine » General Discussions » Finding Molar Mass? (Just another thought)
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