Thursday, April 23, 2009


Why is moon dust sticky? Physicist says he has answer

By analyzing 40-year-old Apollo program tapes, he has concluded that stickiness is influenced by the angle of the sun's rays. The finding could help protect future colonists from a health hazard.

One of the biggest problems facing America's space agency as it prepares to return to the moon is how to manage lunar dust. It gets into everything. Worse, it's sticky, adhering to spacesuits and posing a potentially serious health hazard to future colonists.

Now, a scientist who has been studying the problem off and on over four decades thinks he may have untangled the mystery of why that dust is so sticky. Brian O'Brien, an Australian physicist who worked on the Apollo program in the 1960s, said the sun's ultraviolet and X-ray radiation gives a positive charge to the dust, making it stick to surfaces such as spacesuits.

This doesn't happen on Earth because our atmosphere screens out much of the sun's harmful radiation.

The moon's atmosphere is so thin that the rays easily reach the surface.

O'Brien's most important finding, at least for NASA's purposes in planning for a return to the moon by 2020, is that the angle of the sun's rays influences the stickiness. The more direct the sunlight, he said, the stickier the dust.

O'Brien's interest in lunar dust dates to 1965, when he was at Houston's Rice University, where he was selected as the lead scientist for seven lunar experiments designed for the Apollo program. He began worrying that lunar dust could clog his devices and ruin the experiments.

Lunar dust is "a bloody nuisance," O'Brien said in a statement.

In 1970, he published a paper showing that lunar dust kicked up by the Apollo 11 lunar module that carried Neil Armstrong and Buzz Aldrin back to space coated the surface of a seismometer left behind on the moon's surface. The ground motion sensor overheated and failed after three years.

More than three decades later, in 2006, O'Brien's fascination with lunar dust was rekindled when he learned that NASA had misplaced the original tapes from his dust-detecting experiments, he said in an e-mail from his home outside Perth, Australia. O'Brien dug up his own collection of 173 tapes and set about trying to understand the behavior of the dust once more.

Now 75 and retired, he traced his desire to unravel the 40-year-old problem to "old-fashioned enduring interest and, I suppose, curiosity."

Over two years of painstaking research, O'Brien tracked the dust accumulating on two solar cells, one horizontal and one vertical, over the course of two lunar days. That may not sound like much time, but a lunar day equals nearly 30 days on Earth.

He found that little dust collected on the horizontal cell in the lunar morning, when the sun's rays were slanted, while more dust adhered to the vertical cell, which more directly faced the rising sun.

The weaker the sun's rays, he found, the weaker the electrostatic forces causing the dust particles to stick, until the dust fell off.

Some scientists believe that one of the greatest challenges for future lunar colonists will be keeping their lungs free of the particles, each thinner than a human hair but sharp as a razor.

Based on his research, which is to be published in the journal Geophysical Research Letters, O'Brien thinks colonists will be able to combat the dust problem with a practical, Earth-tested solution: old-fashioned sunscreen.

There might be other approaches, O'Brien said, but "I leave that stuff to the engineers responsible for the safety of the astronauts."

NASA's Johnson Space Center in Houston, the home of the manned spaceflight program, is working on the dust problem too. Several scientists there have been in contact with O'Brien, according to the center's press office. Officials didn't challenge O'Brien's findings nor did they endorse them.

"There are several models that predict how lunar dust behaves on the moon and very little evidence to validate those models," said Josh Byerly, a public affairs officer at Johnson. "We probably will not know its true behavior until we return."

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