⚡ First detection of lightning on Mars

When one thinks of lightning, the image that comes to mind is that of terrestrial storms. But on Mars, a planet where water is scarce, the idea of electrical discharges seems improbable. However, a recent observation has upended this perception.

Baptiste Chide's team, from the Institute for Research in Astrophysics and Planetology, used the Perseverance rover's microphone to capture unexpected signals. During 29 hours of recording over two Martian years, 55 electrical events were identified. These signals manifest as interference in the microphone's electronics, followed by a real shock wave produced by the discharge. This auditory method has enabled the detection of phenomena that eluded traditional instruments.


These Martian electrical discharges differ radically from those on Earth. On our planet, lightning originates mainly from friction between ice particles in clouds. On Mars, it is the friction of dust grains, lifted by winds or whirlwinds, that generates electricity. Daniel Mitchard, a physicist at Cardiff University, explains that the discharge threshold, linked to atmospheric pressure, is much lower on the red planet (explanation at the end of the article). Thus, Martian lightning bolts are weaker and closer to the surface.

Most of the recorded events coincided with strong winds or the passage of dust whirlwinds near the rover. This close connection with localized storms indicates that the discharges could influence Martian chemistry. Oxidants such as hydrogen peroxide, whose presence was unexplained, could be produced by these electrical phenomena, which has consequences for the search for traces of life (see below).

Capturing these lightning bolts visually remains difficult. Many occur during the day, are very brief, and are often obscured by dust. The largest discharges, originating from the rover itself, are only a few tens of centimeters (a few inches) long. To observe them, high-speed, high-resolution cameras would be needed, which are currently absent on Mars. This limitation, however, opens the way for future, better-equipped missions.


Beyond Mars, this discovery broadens perspectives. This is the first time electrical discharges have been detected on a rocky planet other than Earth. Similar phenomena could exist on Venus or on Titan, Saturn's moon. On Mars, the electrification of dust could even amplify storms by facilitating the lifting of particles, thus playing a role in the global climate cycle.

The implications for space exploration are direct. By quantifying the energy of these discharges, engineers will be able to better protect future missions, including spacesuits for astronauts. The study, published in Nature, marks a step forward in our understanding of the Martian environment. It reminds us that even on seemingly calm planets, electricity can arise unexpectedly.

The electrical discharge threshold on Mars

The discharge threshold, or 'breakdown threshold', is a key concept for understanding why lightning on Mars differs from that on Earth. It represents the amount of electrical charge needed for a cloud of particles to discharge into the atmosphere. On Earth, atmospheric pressure is about one atmosphere, which makes the air more insulating. Thus, about three megavolts per square meter are required for lightning to occur, necessitating significant charge accumulations in thunderclouds.

On Mars, the pressure at the surface is only 0.006 atmospheres, which considerably reduces the insulating effect of the air. Consequently, the discharge threshold is much lower, around 15 kilovolts per square meter. This difference means that lesser amounts of charge, generated by dust friction, are enough to cause electrical discharges. That is why Martian lightning bolts are weaker and more localized near the surface.

Atmospheric composition also plays a role. Earth's atmosphere, rich in nitrogen and oxygen, is a good electrical insulator. On Mars, the atmosphere is primarily composed of carbon dioxide, which alters the electrical properties. These combined factors explain why discharges on Mars resemble static sparks more than large terrestrial lightning bolts, with implications for the safety of equipment on missions.

Understanding this threshold helps predict where and when these phenomena can occur, essential for future robotic or human explorations. It allows for the design of electronic systems resistant to electrical interference, ensuring the reliability of missions on the red planet.