Mean Molecular weight

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

In article ,
(Harvey) wrote:

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

--
We have discovered a therapy ( NOT a cure )
for the common cold. Play tuba for an hour.