On the moon, nothing is a valuable resource. The lunar surface is a nearly pure vacuum, making it a potentially important site for high-tech industrial processes. The total amount of gas spread over the moon's entire surface - which has an area equal to that of Africa - is less than 50 metric tons. The moon owes its lack of atmosphere to the Sun. Solar wind and ultraviolet light ionize gas atoms, making them susceptible to transport by the interplanetary magnetic field. Half the atoms escape into space and the rest are driven into the lunar surface.

In 1974, in the publication Nature, Richard Vondrak of NASA's Goddard Research Center in Greenbelt, Maryland, pointed out that lunar vacuum "is a fragile state that could be modified by human activity." He urged that it be "treated carefully if it is to be preserved."

At the time Vondrak wrote, his concern was not merely academic. In the early 1970s, not a few engineers within NASA expected that the Space Shuttle would lead to a return to the moon in the 1980s. Lunar outposts where experiments in moon mining and industrial processes might be conducted would follow soon after.

Vondrak estimated that, owing to life support system and space suit leakage and rocket exhaust, the six Apollo landing missions each doubled the mass of the moon's atmosphere. It returned to normal after a month, leading Vondrak to assert that "small lunar colonies" and modest mining would "present no lasting hazard to the lunar environment."

If, however, more "vigorous" human activity pumped up the lunar atmosphere to a mass of one billion metric tons, solar wind and ultraviolet would be unable to ionize more than its outermost fringe. The thin atmosphere would then persist for centuries even if no more gas were added, Vondrak wrote.

Vondrak looked briefly at the far-out prospect of creating an Earth-density atmosphere on the moon by vaporizing oxygen-rich lunar dirt using nuclear blasts. He estimated that this would need 10,000 times the U.S. nuclear arsenal, making it "impractical that such an amount of gas could be generated by current technology."

References:

"Creation of an Artificial Lunar Atmosphere," Richard R. Vondrak, Nature, Vol. 248, April 19, 1974, pp. 657-659.