Mars Dust Devils Spark Tiny Lightning Bolts Across Red Planet Surface

Accidental Discovery Solves Ancient Mystery

For decades, scientists suspected that lightning might crackle across Mars, but proof remained elusive until an extraordinary stroke of luck. NASA's Perseverance rover has recorded the sounds of electrical discharges and mini-sonic booms in dust devils on Mars, confirming a long theorized phenomenon through audio and electromagnetic recordings captured by the rover's SuperCam microphone. The detection was made by a microphone on the rover's SuperCam instrument designed to analyze the acoustics of Martian rocks zapped by the SuperCam laser, and researchers initially attributed intriguing clapping sounds to dust grains striking the microphone's membrane.

On September 27, 2021, a dust devil passed directly above the rover while the microphone was recording. Such flyovers are relatively rare, having occurred only a handful of times since the start of the mission. That the microphone was recording was even luckier, since it only operates for a few minutes every couple of days to save energy and data bandwidth. The connection clicked for researcher Baptiste Chide while attending a conference on atmospheric electricity a year later.

SuperCam has recorded 55 distinct electrical events over the course of the mission, beginning on the mission's 215th Martian day, or sol, in 2021. Sixteen have been recorded when dust devils passed directly over the rover. Based on six of the seven recorded thunderclaps, most discharges were tiny, just 0.1 to 150 nanojoules, while an average bolt of cloud-to-ground lightning on Earth discharges about a billion joules.

Static Electricity on a Planetary Scale

Scientists theorized that the friction generated by tiny dust grains swirling and rubbing against each other in Martian dust devils could generate enough of an electrical charge to eventually produce electrical arcs through the triboelectric effect, which is the phenomenon at play when someone walks over a carpet in socks and then touches a metal doorknob, generating a spark. Electrical sparks form when dust particles in the swirling column rub and collide, building up static electricity. When the charge gets strong enough, it discharges as a tiny spark.

These sparks aren't dramatic lightning bolts like on Earth — they're tiny, localized and only centimeters long. On Mars, where the surface pressure is just 0.006 atmospheres, there is less insulating atmosphere for an electrical discharge to overcome, so the breakdown threshold is much less, around 15 kilovolts per square meter. The low atmospheric pressure and the high concentration of carbon dioxide, which attenuates sound at high and mid frequencies, severely limit how far sound can travel. In that environment, two people standing together "would have to scream to hear each other."

Chemical Implications for Life

The presence of these electrical discharges means that the Martian atmosphere can become sufficiently charged to activate chemical reactions, leading to the creation of highly oxidizing compounds, such as chlorates and perchlorates. These strong substances can effectively destroy organic molecules on the surface and break down many atmospheric compounds, completely altering the overall chemical balance of the Martian atmosphere.

Finding the electrical discharges has solved a major Martian mystery, namely the origin of oxidants such as hydrogen peroxide on the Red Planet, which was discovered on Mars in 2003. These oxidants can react with organic molecules, potentially destroying biosignatures, while other chemical reactions triggered by the lightning can generate new organic molecules. The "small and frequent static-like discharges could prove problematic for sensitive equipment."

Future Mars Exploration

An obvious implication is that it can help inform the design of future Mars exploration technology to protect it from the electrical discharges we now know occur. According to researchers, "The current evidence suggests it is extremely unlikely that the first person to walk on Mars could, as they plant a flag on the surface, be struck down by a bolt of lightning." However, the discovery opens entirely new research possibilities for understanding Martian atmospheric chemistry and climate patterns.

This study opens a notable field of investigation for the atmosphere of Mars and motivates the development of new atmospheric models to account for electrical phenomena and their consequences in the Martian atmosphere. As humanity prepares for eventual crewed missions to Mars, understanding these electrical phenomena becomes crucial for both equipment protection and our broader comprehension of the Red Planet's dynamic atmosphere.