Friction between dust particles on Mars probably produces electrical discharges akin to lightning, new research has found. However, the sparks are modest relatives of Earth’s mighty bolts and pose no threat to rovers, nor future human explorers.
Mars has so much fine dust storms, it can sometimes envelop almost the entire planet, rudely interrupting our best views. Despite the lack of rain clouds, scientists have worried since the days of the first landers whether these particles could transfer electrons when bumping into each other, generating electric fields strong enough to produce powerful discharges. The fact no lander or rover appears to have been damaged in this way suggests the danger is not too great, with lost missions having more likely explanations.
Volcanologist Professor Josef Dufek of the University of Oregon has created a model of such storms using the closest Earth materials. In Icarus Dufek and co-authors report discharges probably occur, but are too weak to pose much threat. Humans and our robot emissaries will be protected by the limited capacity of the Martian atmosphere to store charge.
"We were interested in pursuing this work because of the number of new missions to Mars and the potential of constraining observations,” Dufek said in a statement.
A typical Martian electrical discharge would have an electric field of about 20,000 volts per meter, Dufek reports. Impressive as that sounds, on Earth 3 million volts per meter is not unusual, creating the spectacular phenomena we are familiar with, often with extraordinary consequences.
"Our experiments, and those of others before us, suggest that on Mars it is easy to get sparks when you agitate sand or dust," co-author Joshua Méndez Harper said. "However, it may be difficult, even in large dust storms or within dust devils, to get very large discharges or conventional lightning.”
Experiments have been conducted before to test the prospects of lightning on Mars, but these had known flaws. Not only were the dust particles used non-Martian, but they contacted the walls of the containers in which the experiments were run. “The interaction of two chemically-dissimilar materials can produce more intense charging than the interaction between two chemically-identical materials,” the paper notes.
Naturally, Dufek and Méndez Harper couldn’t obtain any actual Mars dust, but they noted the similarities between what is there and pulverized basaltic ash from Mexico's 2,000-year-old Xitle volcanic eruption. They swirled these in 8 millibars of carbon dioxide, representing the barely-there Martian atmosphere, inside a glass tube wide enough the particles never touched the walls.
The results are less akin to terrestrial lightning and closer to the small-scale discharges that occur in volcanic vents on Earth, the paper concludes.
All of which suggests the major inaccuracy in the otherwise scientifically reliable book/film The Martian remains. Dust storms on Mars may be terrible for visibility but are unlikely to create anything severe enough to force immediate evacuation.