For the first time, scientists have determined how fast lunar dust accumulates and found that it builds up very slowly, forming a layer about a millimetre thick every 1,000 years.
When Neil Armstrong took humanity's first otherworldly steps in 1969, he didn't know what a nuisance the lunar soil beneath his feet would prove to be.
The scratchy dust clung to everything it touched, causing scientific instruments to overheat and, for Apollo 17 astronaut Harrison Schmitt, a sort of lunar dust hay fever.
The annoying particles even prompted a scientific experiment to figure out how fast they collect, but NASA's data got lost. Now, more than 40 years later, scientists have used the rediscovered 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, their calculations show - just fast enough to form a layer about 0.04 inches thick every 1,000 years. Yet, that rate is 10 times previous estimates.
It's also more than speedy enough to pose a serious problem for the solar cells that serve as critical power sources for space exploration missions. "You wouldn't see it; it's very thin indeed," said University of Western Australia Professor Brian O'Brien. "But, as the Apollo astronauts learned, you can have a devil of a time overcoming even a small amount of dust," said O'Brien, a physicist who developed the experiment while working on the Apollo missions in the 1960s.
That faster-than-expected pile-up also implies that lunar dust could have more ways to move around than previously thought, O'Brien, who led the new analysis, added. In his experiment, dust collected on small solar cells attached to a matchbox-sized case over the course of six years, throughout three Apollo missions. As the granules blocked light from coming in, the voltage the solar cells produced dropped. The electrical measurements indicated that each year 100 microgrammes of lunar dust collected per square centimetre. At that rate, a basketball court on the Moon would collect roughly 450 grammes of lunar dust annually.
"While solar cells have become hardier to radiation, nothing really has been done to make them more resistant to dust," said Monique Hollick, O'Brien's colleague on the project. "That's going to be a problem for future lunar missions," Hollick said. The study appeared in the journal Space Weather, a publication of the American Geophysical Union.