The newly landed Perseverance rover doesn’t need to worry about getting struck by lightning or Mars’ electrical charge affecting any of its mechanical operations. According to a new study, the red planet does not give off a strong enough electrical discharge to do any damage, whether to roaming robotic labs or future human inhabitants.
Scientists have raised questions about potential electrical activity on Mars since the 1970s but previous experiments to determine if spark discharges could occur have been inconclusive due to a variety of experimental conditions. Some research used testing enclosures that did not accurately mimic Mars-like conditions, while others used stand-in particles made of materials not characteristic of a Martian dust storm.
“We set out to determine whether the sparks observed in previous works were representative of Mars or merely experimental artifacts," said Joshua Méndez Harper, a research engineer in the University of Oregon’s Center for Volcanology.
Méndez Harper and his team used basaltic ash from Mexico's Xitle volcanic eruption about 2,000 years ago as a stand-in for Martian dust. In previous experiments, the testing enclosures used posed a problem as the particles came into contact with the walls, causing an uncharacteristic effect. To avoid this, the researchers used sealed, vertical glass tubes about the size of a water bottle. They then created triboelectric charging by colliding particles of basaltic ash.
The collisions occurred at frictional velocities expected to occur during a light Martian breeze, without the particles touching the outer walls and in a pressurized, atmospheric pressure of 8 millibars of carbon dioxide, similar to that found on the Martin surface.
To ensure they were on the correct path, the research team conducted experiments in which the particles made contact with the outer walls of the test chamber—a surfaces foreign to conditions on Mars. “Sparks” occurred in both sets of experiments, the addition of an artificial wall changed the polarity of the discharges, confirming, as suspected, the inconclusive results of previous experiments.
While electrical charges did occur in the Martian-like test chamber, confirming Martian dust devils and storms are indeed possible, the discharges were small. The researchers calculated the charges at about 20,000 volts per meter. By comparison, Earth’s atmosphere can withstand electrical fields reaching 3 megavolts per meter.
“It may be difficult, even in large dust storms or within dust devils, to get very large discharges or conventional lightning because the Martian atmosphere is bad at storing charge,” said Méndez Harper. “Martian dust devils may appear to sparkle, crackle or faintly glow as they roll across Mars' desiccated landscape but with discharges so small that they may not be visible except through detection of their radio waves.”
Nevertheless, Jezero crater, the landing site for Perseverance, seems to regularly experience dust storms in the fall and winter. The research team said this may provide ideal opportunities for electrostatic observations.
"We were interested in pursuing this work because of the number of new missions to Mars and the potential of constraining observations," said Josef Dufek, director of the Oregon Center for Volcanology. "Quantifying charging and discharging behavior has a bearing on the transport of dust in the atmosphere and has long been studied in relation to modulating chemical reactions, including synthesizing organic compounds."
A key objective for Perseverance’s mission is to assess past environmental conditions. Evidence for a more substantial atmosphere in the past would have a bearing on the planet's electrical environment and how it has changed over time.
Photo: This still image is part of a video taken by several cameras as NASA’s Perseverance rover touched down on Mars on Feb. 18, 2021. A camera aboard the descent stage captured this shot.