NASA Rover Detects Electric Sparks in Mars Dust Devils, Storms

Perseverance has confirmed a long-suspected phenomenon in which electrical discharges and associated shock waves can be generated inside the Red Planet's mini-tornadoes.

NASA's Perseverance rover has recorded the sounds of electrical discharges (sparks) and mini-sonic booms in dust devils on Mars. This phenomenon, long theorized, has now been confirmed by audio and electromagnetic recordings captured by the rover's SuperCam microphone. Opening, published November 26 in the journal Nature, has implications for the chemistry of the Martian atmosphere, climate and habitability and could help design future robotic and human missions to Mars.

A common phenomenon on the Red Planet, dust devils are formed from rising and rotating columns of warm air. Air near the planet's surface heats up when it comes into contact with the warmer ground and rises through the denser, cooler air overhead. As other air moves along the surface to take the place of rising warmer air, it begins to rotate. As the incoming air rises into the column, it picks up speed, as if skaters spinning on ice bring their arms closer to their bodies. The rushing air also picks up dust, and a dust devil is born.

SuperCam recorded 55 different electrical events over the course of the mission, starting on the 215th Martian day, or sol, in 2021. Sixteen were recorded as dust devils passed directly above the rover.

Decades before Perseverance landed, scientists theorized that the friction created by tiny dust grains swirling and rubbing against each other in Martian dust devils could generate enough electrical charge to eventually form electrical arcs. This phenomenon, called the triboelectric effect, occurs when someone walks across carpet wearing socks and then touches a metal doorknob, causing a spark. In fact, this is about the same level of discharge that a Martian dust devil would produce.

“Triboelectric charging of sand and snow particles is well documented on Earth, especially in desert regions, but it rarely results in true electrical discharges,” said Baptiste Chide, a member of the Perseverance science team and a planetary scientist at L'Institut de Recherche en Astrophysique et Planetologie in France. “On Mars, the thin atmosphere makes this phenomenon much more likely because the amount of charge required to produce sparks is much lower than what is required in Earth's near-surface atmosphere.”

Perseverance SuperCam tool carries a microphone to analyze the sounds of the tool's laser as it hits rocks, but the team also recorded sounds of wind and even first audio recording of the Martian dust devil. Scientists knew that it could detect electromagnetic interference (static) and the sounds of electrical discharges in the atmosphere. What they didn't know was whether such events happened often enough or whether the rover would ever get close enough to detect them. They then began to evaluate the data collected during the mission and soon discovered the characteristic sounds of electrical activity.

“We have some good models in which you can clearly hear the 'clicking' sound of the spark,” said co-author Ralph Lorenz, a scientist at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland. “On the Sol 215 dust devil recording, you can hear not only the electrical sound, but also the dust devil wall moving over the rover. And on the Sol 1296 dust devil recording, you hear all of that plus some particles impacting the microphone.”

Another thirty-five emissions were associated with the passage of convective fronts during regional dust storms. These fronts are characterized by intense turbulence, which promotes triboelectric charging and charge separation, which occurs when two objects touch, transfer electrons, and separate—part of the triboelectric effect that results in a spark of static electricity.

The researchers found that electrical discharges do not appear to increase during seasons when dust storms, which increase the presence of atmospheric dust worldwide, are more common on Mars. This result suggests that electrical charge accumulation is more closely related to localized turbulent lifting of sand and dust, rather than just high dust densities.

Proof of the existence of these electrical discharges is a discovery that radically changes our understanding of Mars. Their presence means the Martian atmosphere could become charged enough to activate chemical reactions leading to the creation of highly oxidizing compounds such as chlorates and perchlorates. These powerful substances can effectively break down organic molecules (which make up some of the components of life) on the surface and destroy many atmospheric compounds, completely changing the overall chemical balance of the Martian atmosphere.

The discovery could also explain the mysterious ability of Martian methane to disappear quickly, offering an important piece of the puzzle for understanding the limits that life might have faced, and therefore the planet's potential to be habitable.

Given the ubiquitous presence of dust on Mars, the presence of electrical charges generated by particles rubbing against each other is likely to also influence dust transport on Mars. How dust moves across Mars plays a central role in the planet's climate but remains poorly understood.

Confirming the presence of ESD will also help NASA understand the potential risks to electronic equipment on current robotic missions. The fact that no adverse ESD effects have been reported on the Martian surface over several decades of operation may indicate careful spacecraft grounding practices. The results could also serve as a basis for developing safety measures for future astronauts exploring the Red Planet.

The Southern California Jet Propulsion Laboratory, operated for NASA by the California Institute of Technology, built and operates the Perseverance rover on behalf of the agency's Science Mission Directorate as part of NASA's Mars Exploration Program portfolio.

To learn more about Perseverance, visit:
https://science.nasa.gov/mission/mars-2020-perseverance

DC Eagle
Jet Propulsion Laboratory, Pasadena, California.
818-393-9011
[email protected]

Karen Fox / Molly Wasser
NASA Headquarters, Washington
202-358-1600 / 240-419-1732
[email protected] / [email protected]

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