A Guide to Physics Problems. Part 2. Thermodynamics, Statistical Physics, and Quantum Mechanics

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The acceleration of gravity (see also Problem 1.10, Part I)

where M is the mass of the Moon and is the average density of the Moon
(which we consider to be uniform). Therefore,

where we have set Now, from (S.4.7.2) and (S.4.7.4), we have

where is the pressure on the surface of the Moon.

which implies that it is not impossible to have such cavities inside the Moon
filledwith gas (to say nothing of the presence of lunars).

THERMODYNAMICS AND STATISTICAL PHYSICS