Question

The atmosphere on a planet is possible only if [where $v_{rms}$ is root mean square speed of gas molecules on planet and $v_e$ is escape speed on its surface]

• A. $v_{\text{rms }}=v_e$
• B. $v_{rms}>v_e$
• C. $v_{\text{rms }}\le v_e$
• D. $v_{\text{rms }}<v_e$

Answer 1

Answer: (D)

The atmosphere on a planet is possible only if $v_{rms}<v_e$
If $v_{\text{rms }}\ge v_{\text{escape }}$ the gas molecules will leave the surroundings of the planet, i.e., will be free from gravitational pull of the planet.