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The powdery lunar soil was great for making footprints, but was a problem for astronauts like Charlie Duke, shown here during the Apollo 16 mission in 1972. It got in their eyes and throats, and clung stubbornly to every surface. (NASA)

Stronger Than Dirt

Lunar explorers will have to battle an insidious enemy—dust.

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ANOTHER LUNAR DAWN, and the powdery dust on the moon’s surface begins to stir. Without a breath of wind, the finest motes swirl across the ancient landscape as electrostatically charged dust grains repel one another. Larger grains join the dance in a line that stretches more than 3,000 miles from the lunar north pole to the south pole, along the edge of advancing daylight.
Within hours the dance has become frenzied and vertical, with microscopic grains hurtling miles overhead, the tiniest ones flying the farthest, until the weak lunar gravity stops their rise and pulls them back to the dusty surface. Instead of resting there, many jump up to begin the dance anew, surrounding the moon with a veritable atmosphere of dust—glassy, abrasive, toxic grit that could spell “No Trespassing” to future explorers.

Under a cloudless blue Colorado sky, I accompanied seven scientists, a graduate student, and an education specialist as they toiled up the shifting sands of the tallest dunes in North America. At 8,200 feet above sea level, the intense sunlight scorched our skin even though it was October, and in the thin air, the exertion left us panting. The incessant wind quickly smoothed away our footprints. We were in the Great Sand Dunes National Park and Preserve, but it felt as though we were alone on Mars.

And that was the idea.
We were there to study the problems awaiting NASA engineers planning the next generation of lunar outposts and Mars expeditions. Four of the scientists carried miniature Mars rovers that looked like the kind of radio-controlled toy you might find at RadioShack. They had thought about bringing NASA’s one spare of the Sojourner rover from the 1997 Mars Pathfinder expedition, “but the commercial truck chassis were far cheaper,” explained team leader Masami Nakagawa, an associate professor of mining engineering at the Colorado School of Mines in Golden. Each of the model trucks had been modified for this expedition: transmissions geared down, engines souped up, the body of one turned into a rotating auger for digging in the sand.

For two eight-hour days under the broiling sun, scarcely breaking for granola bars or water, the scientists took turns at the radio controls to put the rovers through their paces. The vehicles were sent climbing the steep dunes until half-buried by avalanches, while cameras and a crude duct-tape tape measure (the real thing had disappeared in the soft sand) documented their progress, or lack thereof. “Hey, I think sand and dust finally jammed the transmission!” exulted grad student Jared Reese, holding aloft the auger vehicle, which had finally refused to budge, even with a freshly charged battery.

Celebrating when the equipment stops working? That was in fact the purpose of this NASA-sponsored “Dust-Off”: to court Murphy’s Law. “Over the next two days, our interdisciplinary team can get a direct feel for how invasive dust is,” explained Nakagawa over the first night’s dinner, at the Great Sand Dunes Oasis restaurant. “We want to look at lunar and Martian dust mitigation from a systems engineering viewpoint.”
By “dust,” Nakagawa doesn’t mean house dust. Most of the stuff that collects on furniture is actually organic material like dead human skin cells, pet dander, and pollen grains. For the most part, it’s soft: Wipe it off with a cloth and it won’t scratch polished wood. And it’s usually not thick. Even an attic corner that hasn’t been swept in years can accumulate less than an eighth of an inch.

On Earth, the closest equivalents to lunar and Martian dust are the choking storms that sometimes blow west from the Gobi Desert to blanket Beijing with millions of tons of ultrafine particles. In 1980 powdery volcanic ash fell an inch deep hundreds of miles from Washington’s Mount St. Helens, and “white outs” of alkali gypsum dust swept the Nevada playa just after the 2002 Burning Man arts festival. But even these aren’t good analogs. In terrestrial deserts the atmosphere is too dense, the soils too humid, the plants too numerous, and the weathering from wind and water too prevalent to match conditions on the moon or Mars.

Lunar dust is razor-sharp grit made of inorganic stone and powdered glass. It was formed over hundreds of millions of years by micrometeorites slamming into the moon at high velocities, fracturing lunar rocks into shards and melting the sand into glass. The Apollo astronauts who trod the inches-deep regolith (the preferred term for extraterrestrial dirt) discovered what a nuisance it could be. Wipe a spacesuit’s sun visor, and it scratched the protective layer of gold. Get dust into the spacesuit’s joints, and it fouled the attachments and seals. Try to brush the grit off a spacesuit before reentering the lunar lander, and its sharp edges dug into the fabric. Track it inside the habitat, and it became airborne. Breathe it in and mucous membranes swelled shut (“I didn’t know I had lunar dust hay fever,” commented Apollo 17 geologist-astronaut Jack Schmitt at the time). Go back out, and the graphite-black dust had so darkened the white spacesuits (“Looks like you guys have been playing in a coal bin,” quipped mission control during the Apollo 16 mission) that the fabric absorbed rather than reflected the murderous sunlight, overheating the astronauts’ life support systems.

And that’s just the moon.
On Mars, the dust may be corrosive and poisonous too. Martian soil is expected to be a strong oxidizer (think of powdered bleach or lye) laced with heavy metals such as hexavalent chromium, the carcinogen in the movie Erin Brockovich. It’s also, as engineers operating NASA’s Mars rovers have learned, magnetic. Photographs taken by Spirit and Opportunity show Martian dirt, reddish with oxides of iron, coating magnets on the vehicles. On the moon, glass in the regolith is filled with microscopic beads of pure iron—so-called nanophase iron. In both places the dirt is likely to stick to anything with an electromagnet, including motors and electronics.

A mere two days in the Colorado dunes was enough to convince me of the insidious mechanical challenges that dust will present to future astronauts and their machines. The windborne grit scoured our skin raw, sifted into hair and zippers and shoes, messed up the transmissions of all four rovers, and jammed the buttons of cellular phones.

Even on the airless moon, the dirt doesn’t lie still. Astronauts in lunar orbit aboard the Apollo 8, 10, 15, and 17 spacecraft repeatedly observed and sketched what they variously called “bands,” “streamers,” or “twilight rays” for about 10 seconds before lunar sunrise or sunset. The drawings are reminiscent of the slanting rays that filter up through clouds during sunsets on Earth. Some scientists chalked the phenomenon up to light reflecting from dust suspended above the lunar surface, but others remained unconvinced: Without an atmosphere, how could dust be suspended above the moon? Even if the particles were kicked up by, say, a meteorite impact, they would quickly settle back to the surface.

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