Richard Leis

Dust Devils on Mars

Standing kilometers tall, roaming the desert in crisscrossing paths, vacuuming or depositing dust, and possibly contributing to albedo (surface light reflection) and climate changes, images of dust devils in motion on Mars have been captured by the Mars Exploration Rover Spirit. Spirit captured images of gusts and whirlwinds full of dust marching across Gusev Crater toward the rover on May 31, 2005. Scientists then enhanced the contrast in the images and pieced them together in consecutive order to create a movie depicting the violent movement of dust in the thin martian air.

The sand and dust in dust devils can whirl around at greater than 30 meters per second (70 miles per hour). Because the air is thin, even hurricane-speed winds exert little pressure on objects, but over time eolian (wind) erosion has left its mark on the Red Planet. In some areas winds have stripped out weaker rock leaving parallel depressions called yardangs lined up in the direction of the prevalent winds. In others, the eroded sand and dust has been deposited into sand dunes or wide-area dust deposits, effectively burying other landforms.

In a paper entitled “Three decades of Martian surface changes” by Paul E. Geissler from the U.S. Geological Survey in Flagstaff, Arizona, USA suggests that dust devil activity during the summer in mid to high latitudes of Mars may contribute to albedo changes over several years or decades. As dust devils race across the surface they pick up sand and dust, revealing the darker bedrock beneath and decreasing albedo in the region. This darkening, when viewed up close, is caused by overlapping dust devil tracks. In areas where brighter sand and dust are deposited, albedo may increase.

NASA scientists believe dust devils could be potentially dangerous to visiting astronauts and their equipment. Aside from impacts from high-velocity sand and dust, astronauts may need to worry about electrical discharges around dust devils as well. Arcs of electricity between the dust devil and astronauts, vehicles or other equipment could fry unprotected electronics or interfere with communications. The electrostatic charge in individual grains of material may adhere sand and dust to space suits and other equipment. Habitats on Mars will need to take this into account to prevent contamination of living areas from outside particles.

Scientists will continue to collect data about dust devils on Mars and here on the Earth to better understand these dangers and create technological solutions. The data will also help them better understand how dust devils are created, the mechanics behind their motion across surfaces, and how they contribute to climate and other planetary and regional characteristics.

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Richard Leis

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