Mean Molecular weight

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Harvey - 26 Nov 2004 07:47 GMT

Hi

Please can someone help.

Why is it that when the mean molecular weight is quoted for a planet
it ONLY refers the the planet's atmosphere. Why is it that the actual
composition such the solid part of the planet is NOT included.

All comment welcome

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Tom Kirke - 29 Nov 2004 19:08 GMT

> Why is it that when the mean molecular weight is quoted for a planet
> it ONLY refers the the planet's atmosphere. Why is it that the actual
> composition such the solid part of the planet is NOT included.

Because MMW has some use in calculating gas dynamics ( temperatures,
pressures, etc. ). It does not show up much in solid body calculations.

Also it is awkward to calculate the MMW for things like a planetary core.
For example, we know the mass of the Earth's core, but how many *molecules*,
not atoms, are present in crystalline Fe?

Dark skies,

tom

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Space Forum / Astronomy / November 2004

Mean Molecular weight