NASA rover detects electrical discharges - 'mini-lightning' - on Mars

"The electrical charges required for these discharges are likely to influence dust transport on Mars, a process fundamental to the planet's climate and one that remains poorly understood. What's more, these electrostatic discharges could pose a risk to the electronic equipment of current robotic missions - and even a hazard for astronauts who one day will explore the Red Planet," Chide said.

The researchers analyzed 28 hours of microphone recordings made by the rover over a span of two Martian years, detecting 55 electrical discharges, usually associated with dust devils and dust storm fronts.

"We did not detect lightning by the common definition. It was a small spark, perhaps a few millimeters long, not really lightning. It sounded like a spark or whip-crack," said planetary scientist and study co-author Ralph Lorenz of the Johns Hopkins University Applied Physics Laboratory in Maryland.

Sixteen of the electrical discharges were recorded during Perseverance's two close encounters with dust devils.

Another study published in October documented how dust devils are a common feature on dry and dusty Mars, with two orbiting spacecraft detecting wind speeds reaching around 98 miles per hour (158 kph) in these whirlwinds that hoist dust into the atmosphere.

The internal dynamics of dust devils give rise to the electrical discharges.

"I would call it 'mini-lightning,'" Chide said. "The phenomena are caused by the friction of tiny dust grains rubbing against each other in the air, which builds up electrons and then releases their charge as electrical arcs just a few centimeters long, accompanied by audible shockwaves."

The phenomenon is called triboelectricity.

"Think of a sunny, dry day when you walk on a rug or a rubber surface and bring your hand close to a door handle. The small spark you might generate, and thus experience, is the same kind of electrostatic discharge that we detected with SuperCam on Perseverance," said planetary scientist and study co-author Franck Montmessin of the French research agency CNRS and research laboratory LATMOS.

Electrical activity in the Martian atmosphere had long been suspected.

"What we've observed is a result of having exceptionally sensitive instrumentation observing for a long period, so we can detect very small discharges, about the energy of an automobile ignition," Lorenz said.

Mars joins Earth, Saturn and Jupiter as planets known to have atmospheric electrical activity. Though not yet documented, other worlds in our solar system also may have this feature including the planets Venus and Uranus and Saturn's moon Titan, according to the researchers.

"The Mars atmosphere was looking very favorable for electrification: full of dust, dry and turbulent," Chide said. "On terrestrial deserts on Earth, the electrification of dust and sand is well-documented, but it rarely results in actual electrical discharges. On Mars, however, the thin carbon dioxide atmosphere makes this phenomenon far more likely, as the amount of charge required to generate sparks is much lower than it is on Earth."

SuperCam recorded the very first Martian sounds in 2021, shortly after Perseverance landed.

"Since then, it has been used daily to listen to the atmosphere, compiling a playlist of over 30 hours of sounds from the Red Planet: the howl of the wind, the whir of the (rover-deployed) helicopter Ingenuity's blades, and now, a new track: electrostatic discharges," Chide said.