Chapter 5, Problem 1AS

Explain why the Moon and Mercury possess only very weak, transient atmospheres consisting of constituents temporarily captured from the solar wind or released by collisions with interplanetary debris.

To determine

Why the Moon and Mercury possess only very weak, transient atmospheres consisting of constituents temporarily captured from the solar wind or released by collisions with interplanetary debris.

Answer to Problem 1AS

Both Moon and Mercury possess weak gravitational field which is caused by the dissipation of its atmosphere. Hence, the Moon and Mercury possess only very weak, transient atmospheres.

Explanation of Solution

Mercury is a small planet very close to the Sun; it is hot (having a surface temperature of more than 400 K) and has a low surface gravity (1 g on Mercury equals $3.7{\text{ m/s}}^{\text{2}}$ as opposed to $\text{9}{\text{.8 m/s}}^{\text{2}}$ on Earth). Any atmosphere may once have had escaped long ago because the particles were far too energetic to have been held in by the planet’s weak gravity. Similarly, any original atmosphere the Moon may have had must have dissipated billions of years ago despite its cooler temperature (about 300 K, like that of Earth) because its gravitational field is only about one-sixth as strong as that of Earth.

Conclusion:

Both Moon and Mercury possess weak gravitational field which is caused by the dissipation of its atmosphere. Hence, the Moon and Mercury possess only very weak, transient atmospheres.