El Dorado Valley, Nevada—For the first few hours it seemed as though nothing at all might happen. We would just roast out here all day in the 110-degree desert heat, staring across the expanse of dried-up lake bed without seeing any sign of the “dust devils” (video)—mini-tornadoes—that the scientists and arrays of instruments stood ready to record.
Dust devils, I’d learned before coming here, materialize suddenly in fair weather over very dry ground. All it takes is sunlight and a rising vortex of air to pick up some loose surface sand or dirt and whip the particles into a faint, slender funnel cloud. On Earth, the whirlwinds disintegrate within moments, without inflicting damage on anyone or anything. But on Mars, similar storms unfold on a much larger scale (photograph; video). Dust devils dominate the weather patterns on the Red Planet, sculpting its surface and potentially threatening future robotic explorers or visiting astronauts. Researchers need much more data on how dust devils form and behave in order to construct a meaningful model of Martian climate. This corner of Nevada offers one of the best and most accessible arenas for studying the phenomenon.
Still nothing. Tim Michaels of the Southwest Research Institute in Boulder, Colorado, and Aymeric Spiga from Université Pierre et Marie Curie, Paris, two atmospheric modelers, wax philosophical over bottles of Gatorade. A day when nothing happens, they assure me, is as important as a day of frantic activity: Since no one knows precisely why dust devils form where and when they do, being able to say for sure what does not cause them would represent progress of a kind.
Then our luck turns—in a tall, filmy, swirling pillar that is either a dust devil or a mirage. “Let’s take a picture,” Asmin “Oz” Pathare of the Planetary Science Institute says into his walkie-talkie, a hundred yards away from us. “Three, two, one, go.” As Oz aims and fires the camera on his tripod at Spotter Station A, Patrick Russell from the Smithsonian National Air and Space Museum, standing behind a similarly mounted camera at our Spotter Station B, snaps the same view from a different angle.
Tim and Aymeric point out how the dust devil makes the movement of the air visible. All around us, they say, atmospheric currents tumble in cyclonic or anticyclonic patterns that remain hidden until a dust devil paints them brown.
“Another,” Oz says as the dust devil travels more or less northwest through the study area. “Three, two, one, go.” Weeks from now, after this phase of field activity ends, he will superimpose today’s images on a painstakingly constructed panoramic photomontage of the site, the better to trace each dust devil’s path. For now, Martin Towner of Imperial College London draws the apparent track in pencil on a survey map. His Survey Station (the back end of a rented, dust-encrusted SUV) forms a triangle with the two Spotter Stations (folding canvas sling chairs under beach umbrellas). Martin describes this particular dust devil in coded terminology as a “tiny faint short.” That means it appeared to be less than two meters in diameter, contained so little dust as to remain virtually transparent, and lasted just slightly longer than five seconds, which is the low-end cutoff duration for logging a dust devil in a day’s record of observations.
Martian dust devils unfold on a whole different scale. They grow to gigantic proportions, lifting tons of dust several kilometers high into the orange skies, where the particles hang as haze before drifting back down to the surface. Dust devils occur virtually everywhere on the planet, except for the north and south poles, which lie under layers of wet and dry ice. So far, no dust devil has harmed any spacecraft there. On the contrary, passing dust devils have lent NASA invaluable assistance more than once by whizzing over a stalled Mars rover, sweeping its solar panels clean, so the sun can recharge the craft’s batteries. NASA hopes these close-up Earth-side investigations will help parse the dust devils on Mars, which strongly influence the climate and the erosion of the planet’s surface.