Escape Velocity — No AtmosphereMediumQuestion 30737
Question
The Moon has no atmosphere because:
- AIt is too cold
- BIts escape velocity (2.38 km/s) is too low to retain gas molecules that move at comparable thermal speedsCorrect
- CIt has no magnetic field
- DIt rotates too slowly
Correct answer
Its escape velocity (2.38 km/s) is too low to retain gas molecules that move at comparable thermal speeds
Explanation
Gas molecules have average thermal speeds ~0.5–2 km/s (comparable to Moon's v_escape). Over billions of years, faster molecules escaped and Moon's atmosphere was lost. Earth's higher v_escape (11.2 km/s) retains most atmospheric gases.