How fast moon dust piles up measured for first time

Washington: Neil Armstrong had no idea what nuisance the lunar soil beneath his feet would prove to be after taking the first step on moon more than 40 years back. 

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. Or, so NASA thought. 

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 a millimeter (0.04 inch) 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. But, as the Apollo astronauts learned, you can have a devil of a time overcoming even a small amount of dust," University of Western Australia Professor Brian O'Brien, a physicist who developed the experiment while working on the Apollo missions in the 1960s and now has led the new analysis, said. 

That faster-than-expected pile-up also implies that lunar dust could have more ways to move around than previously thought, O'Brien 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 micrograms of lunar dust collected per square centimeter. At that rate, a basketball court on the Moon would collect roughly 450 grams (1 pound) of lunar dust annually. 

Comparing the effects on cells from dust and from damaging high-energy radiation from the Sun, O'Brien found that long-term dust accretion could diminish the output from shielded power supplies of a lunar outpost more than even the most intense solar outbursts. 

Because the threat posed by radiation damage was recognized early on, solar-cell makers fortified their devices against that sort of harm. 

The research is published in Space Weather, a publication of the American Geophysical Union. 


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