Scientists used rediscovered Apollo data to make the first determination of how fast lunar dust accumulates. It builds up unbelievably slowly by the standards of any Earth-bound housekeeper -- just fast enough to form a layer about a millimeter (0.04 inches) thick every 1,000 years. Yet, that rate is 10 times previous estimates. It's also speedy enough to pose a serious problem for the solar cells that serve as critical power sources for space exploration missions.

Source: Rediscovered Apollo data gives first measure of how fast moon dust piles up