Re: Could we create an atmosphere on the moon?

> Could we create an atmosphere on the moon?

The short answer is, "Yes" (that is, it is possible to do so). The somewhat longer answer is, "Yes, but it would probably not be worth it."

There is likely to be sufficient oxygen (one of the most common elements in the universe) on the Moon to allow us, if we don't mind the expense and time involved, to create a lunar atmosphere of oxygen (and perhaps carbon dioxide as well). However, any lunar atmosphere would not last very long unless it were constantly and massively renewed.

The reason is that the Moon is too small to hold an atmosphere so near to the Sun. Solar radiation acts to strip atmosphere away from any solar system body, so that an atmosphere is a tug-of-war between the planet/moon/asteroid/whatever, which uses gravity to hold on to gases, and the Sun, which is acting to drive the gases away.

[Note from the moderator: the random motion due to thermal energy of the gases also acts to "evaporate" the atmosphere. This depends on temperature(more molecular agitation at higher temperatures), but at "room temperature" this would a significant factor in leaking the Moon's atmosphere from its gravitational grasp.]

This means that the closer an object is to the Sun, the larger it must be to hold an atmosphere, because the intensity of radiation decreases as the square of the distance from the Sun. Compare, for example, Mercury and Titan, two bodies of similar size. Titan is able to hold a thick atmosphere because it is some 25 times further from the Sun than Mercury, which has only the most tenuous of atmospheres.

We could still live on the Moon even if we did not bother to create a lunar atmosphere, as long as we could derive breathable air from local materials. The technique would be to excavate caves (which would also protect us from solar radiation), then pressurize them as living space. But this would only be worthwhile if the air did not need to be shipped from Earth.

Colonists would also require water, which is scarce on the Moon, but in 1994 the Clementine mission seems to have found water ice, shielded from the Sun in deep polar craters on the Moon. One of the tasks of the Lunar Prospector will be to see whether this is in fact the case. If water is available, it would greatly simplify the problems associated with long-term missions to the Moon.

For more information on the Moon in particular and the Solar System in general, go to The Nine Planets.