The ability of a celestial body to retain an atmosphere depends primarily on its gravitational strength (related to mass) and the temperature of the gas (related to molecular velocity). If the escape velocity is less than the thermal velocity of gas molecules, the atmosphere escapes.
There is no atmosphere on the moon because:
Asked in UPPSC Upper Mains 2012 · Topic: Space (Gravitational Fields and Potentials in Space)
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Answer: D. escape velocity of gas molecules on it, is less than the root mean square velocity.
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