Electric discharges detected on Mars for the first time

On Mars, winds constantly stir up whirlwinds of fine dust. It was at the centre of two of these dust devils that the SuperCam instrument's microphone, the first ever to operate on Mars, accidentally recorded particularly strong signals. Analyses carried out by scientists at the Institut de recherche en astrophysique et planétologie (CNES/CNRS/Université de Toulouse) and the laboratoire Atmosphères et observations spatiales (CNRS/Sorbonne Université/Université de Versailles Saint-Quentin-en-Yvelines)¹ showed that they were the electromagnetic and acoustic signatures of electric discharges comparable to the small static electricity shocks that can be experienced on Earth when touching a door handle in dry weather. Long theorised, the existence of electric discharges in the Martian atmosphere has now been confirmed by observation for the first time.

These phenomena can be explained by friction between tiny dust particles:  they become charged with electrons and then release their charges in the form of electric arcs a few centimetres long accompanied by audible shock waves. On Earth, it is well known that dust particles can become electrically charged, especially in desert regions, although this rarely results in actual discharges. On Mars, the thin atmosphere, mostly made up of carbon dioxide, makes this phenomenon much more likely to occur: the amount of charge needed to form sparks is much lower than on Earth.

The discovery of these electrical discharges profoundly changes our understanding of Martian atmospheric chemistry. These phenomena show that the Martian atmosphere can reach sufficient levels of charge to speed up the formation of highly oxidising compounds. Such substances can destroy organic molecules on the surface as well as numerous atmospheric compounds, thereby profoundly upsetting the photochemical balance of the atmosphere. This discovery could explain the surprisingly rapid disappearance of methane, which has been a subject of scientific debate for several years.

The electrical charges required for these discharges are likely to affect the transport of dust on Mars, thus playing a central role in the Martian climate, the dynamics of which remains largely unknown. They could also pose a risk to the electronic equipment of current robotic missions and constitute a danger to potential future manned missions.

The microphone of the SuperCam instrument aboard NASA's Perseverance rover recorded the very first sounds on Mars in 2021, the day after it landed on the planet. Switched on every day, it has collected over 30 hours of sounds from the Red Planet: the wind blowing, the noise of the blades of the Ingenuity helicopter, and now, electric discharges. This new observation confirms the enormous potential of acoustics as a tool for planetary exploration.