The graph below plots the escape velocity of each planet along the vertical axis and its surface temperature along the horizontal. The lines plotted in the figure are the speeds of the fastest gas particles as a function of temperature for various gases. Which of the gases plotted in the diagram could be retained in the atmosphere of Mars?

Question

Quizplus · Accepted Answer

To be retained in the atmosphere of a planet, a gas must have an escape velocity lower than the planet's escape velocity and not exceed the temperature threshold where its fastest particles exceed the escape velocity. From the graph, we can see that Mars' escape velocity is below the escape velocities of all the gases except for He. Additionally, the temperature threshold for He is very low, indicating that it could not be retained in the atmosphere. For COS and NH3, their fastest particles do not exceed the escape velocity until very high temperatures, so they could be retained in Mars' atmosphere. Therefore, the answer is C, COS, NH3, and O2 could be retained in the atmosphere of Mars. To be retained in the atmosphere of Mars, a gas must have an escape velocity lower than Mars' and not exceed the maximum speed of the gas particles at the given temperature. From the graph, we can see that Mars' escape velocity is around 5 km/s. Both CO₂ and NH₃ have maximum speeds lower than this at all temperatures shown on the graph, which means they could be retained in the atmosphere of Mars. O₂ also has a maximum speed lower than Mars' escape velocity at temperatures below around 900 K, so it could also be retained in the atmosphere of Mars at those temperatures. Therefore, the best choice(s) is C. H₂ has a maximum speed higher than Mars' escape velocity at all temperatures shown on the graph, so it cannot be retained in the atmosphere of Mars. He also has a maximum speed higher than Mars' escape velocity at all temperatures shown on the graph, so it cannot be retained in the atmosphere of Mars.

The Graph Below Plots the Escape Velocity of Each Planet