Small planets/orbits like Moon cannot have atmosphere because of their masses. They don't have enough gravity to hold an atmosphere. Then what is the critical mass that makes enough gravity to keep an atmosphere?
Please explain by Mathematical equations with the data given below:
Density of the planet is uniform everywhere; 5 g/cm3.
The atmosphere consists of pure O2 gas.
Temperature of the the atmosphere is uniform everywhere and fixed to 300K.
What is the critical size of radius or mass of this planet that makes it possible to have an atmosphere?