Particle physics experiments

Experiments reveal electric sparks are possible on Mars

Experiments in a chamber under Martian-like conditions in a University of Oregon lab suggest that small sparks can be triggered by friction under normal atmospheric conditions.

Friction caused by dry Martian dust particles coming into contact with each other can produce an electric shock on the planet’s surface and atmosphere, according to researchers at the University of Oregon.

However, such sparks are likely to be small and pose little danger to future robotic or human missions to the Red Planet, they report in an article published in the journal. Icarus.

Viking landers in the 1970s and orbiters since then have detected silt, clays, windblown bedforms and dust devils on ">March, raising questions about potential electrical activity.

Scientists set out to experimentally determine whether large electrical storms and lightning strikes were possible, and whether static electricity generated by particles from vehicles hitting the planet’s predominantly basalt rock or, possibly, visiting humans in protective gear. would constitute a danger.

Using volcanic ash as a surrogate for Martian dust, researchers in the laboratory of OU volcanologist Josef Dufek have found that electric shocks in Martian dust demons and storms are indeed possible. However, the discharges would likely be low given the weak electric fields, nearly 20,000 volts per meter, sustained by the Martian atmosphere.

Earth’s atmosphere, by comparison, can withstand electric fields of up to 3 mega-volts per meter, producing spectacular frequent and sometimes fatal thunderstorms in the southeastern United States, said Joshua Méndez Harper, research engineer at the Center. of Oregon Volcanology at the Earth Department. Sciences.

“Our experiences, and those of others before us, suggest that on Mars it’s easy to get sparks when you stir up sand or dust,” Méndez Harper said. “However, it can be difficult, even in large dust storms or dust eddies, to get very large discharges or conventional lightning because the Martian atmosphere is bad for storing charge.”

Such anticipated triboelectric or frictional processes are often encountered on Earth by means of socks sliding on a carpet and then touching a doorknob or sticking a balloon on a window after rubbing it on human hair.

Martian dust devils, he said, can appear to twinkle, crackle, or faintly glow as they roll across the parched landscape of Mars, but with discharges likely so small they may not be visible except by detecting their radio waves.

Previous experiments to determine whether spark discharges could occur were inconclusive as the particles were swirled so that they came into contact with the walls of the test chambers. Some experiments have used particles of material not found on Mars. These contacts may have led to an uncharacteristic charge of a Martian dust storm.

“We set out to determine whether the sparks seen in previous work were representative of Mars or just experimental artefacts,” Méndez Harper said.

At UO, Méndez Harper, Dufek and George McDonald, postdoctoral researcher at Rutgers University, bypassed the limitation on wall exposure by using a vertical glass tube comparable in size to a water bottle measuring about 4 inches in diameter and 8 inches in length.

They created a triboelectric charge by colliding basalt ash particles from the Xitle volcanic eruption in Mexico about 2,000 years ago.

The collisions in the sealed tubes occurred at the friction speeds expected during a light Martian breeze, without the particles touching the outer walls and under a pressurized atmospheric pressure of 8 millibars of carbon dioxide, similar to that found on the Martian surface.

The Mexican basalt used in the project is similar to Martian basalt, as detected by rovers in the Pathfinder and Mars Exploration Rover missions and dust analogues developed by ">NasaJet propulsion laboratory of.

For comparison, the research team conducted experiments in which the particles were allowed to come in contact with surfaces alien to the conditions predicted on Mars. Sparks occurred in both sets of experiments, but the addition of an artificial wall changed the polarity of the discharges.

“We were interested in continuing this work because of the number of new missions to Mars and the potential for constraining observations,” said Dufek, professor in the Department of Earth Sciences and director of the Oregon Center for Volcanology. “The quantification of charge and discharge behavior affects the transport of dust in the atmosphere and has long been studied in relation to the modulation of chemical reactions, including the synthesis of organic compounds.”

NASA’s Mars mission that landed on February 18 includes the Perseverance rover and the Ingenuity robotic helicopter.

The low discharge energy on Mars indicated by the new experiments means these effects are unlikely to impact mechanical operations, Dufek said.

Nonetheless, Jezero Crater, the landing site of Perseverance, appears to experience regular dust storms in the fall and winter. This, McDonald said, may provide opportunities for rudimentary observations of electrostatic phenomena.

One of the objectives of the Perseverance mission is to assess past environmental conditions. Evidence of a more substantial atmosphere in the past would affect the electrical environment of the planet and how it changes over time.

“The big takeaway from this study is that Mars can be an electrically active place, albeit quite differently from Earth,” Dufek said. “The fact that analog Mars dust easily charges to the point of discharge even when the grains aren’t rubbing against other surfaces suggests that future settlers might find a world altered by static electricity in subtle ways. “

Reference: “Detection of spark discharges in an agitated Mars dust simulant isolated from foreign surfaces” by Joshua Méndez Harper, Josef Dufek and George D. McDonald, December 11, 2020, ICARUS.
DOI: 10.1016 / j.icarus.2020.114268

The National Science Foundation funded the research with a grant to Dufek. Méndez Harper was supported by a Blue Waters Graduate Scholarship.