Listen to the crackle of Martian ‘mini-lightning’

When the wind blows on Mars, electricity crackles through the air.

For the first time, scientists have detected electricity in the Red Planet’s atmosphere. A microphone on NASA’s Perseverance rover captured the sounds and electrical interference of dozens of electrical discharges generated by colliding dust grains, researchers report November 26 in Nature.

The jolts are relatively small, packing a punch that’s akin to the shock from touching a doorknob on a dry, winter day. Nonetheless, they could pose a hazard for future astronauts and electronics and hamper the search for Martian life, if it ever existed, the researchers warn.

It’s “like mini-lightning,” says planetary scientist Baptiste Chide of the University of Toulouse in France. He describes them as “centimeter-scale electric arcs that produce a crack … a shock wave.” There are thousands of kilometers of dust storm fronts on Mars that can generate these jolts, he says, so “we think there are plenty of these small discharges happening en masse.”

When airborne particles slide against or bump into each other, their surfaces can become charged like two balloons rubbed together. On Earth, countless such interactions occur within sandstorm and volcanic ash plumes, leading to the buildup of electrical fields that eventually discharge as arcs of electricity. This phenomenon is called triboelectricity.

For decades, lab experiments and computer simulations have suggested that triboelectricity also flashes within dust storms and dust devils on Mars. But no one had ever detected it.

Chide and his colleagues had previously recorded the sounds of a Martian dust devil, attributing a loud clicking noise to grains striking the microphone. But after hearing scientists at a conference discuss Martian triboelectricity, Chide realized the click may have been a zap.

For confirmation, his team simulated the electrical interference the microphone would experience from a nearby discharge. Then they compared the results to the actual interference the microphone experienced. The signatures matched perfectly.

Excited, the researchers reviewed 28 hours of recordings taken over two Martian years. A total of 55 discharges occurred within about two meters of the microphone, they found. Most occurred in the windiest periods, with sixteen during dust devil encounters. Using the microphone’s measurements of the discharges’ pressure waves, the researchers estimated that the largest packed 40 millijoules of energy. That’s comparable to the zap of an electrical bug swatter, Chide says.

“There’s no doubt in my mind that it was an electrical signal that they measured,” says electrical engineer Joshua Méndez Harper of Portland State University in Oregon. Now, he says, the question is: “How was it influenced by the rover?” While triboelectrification probably occurs in the vehicle’s absence, he adds, it could behave differently.

The jolts won’t kill astronauts, Chide says, but they could degrade spacesuits over time and disrupt spacecraft electronics and instruments.

What’s more, the zaps could obscure the search for evidence of Martian life. The discharges may spark a reaction that generates oxidants like hydrogen peroxide, which can destroy organic molecules, Chide says. The rock and soil samples taken and left behind by Perseverance for later collection are probably protected because they’re stored in insulated tubes with electrostatic paint, he says, though they could still have been zapped prior to sampling.

“This discovery calls for a next generation of instruments dedicated to measuring electric fields at the surface of Mars … to better quantify this phenomenon,” Chide says.