For the first time, scientists have detected a lightning-like discharge on Mars! While orbiting the red planet, NASA’s MAVEN spacecraft recorded a mysterious electromagnetic signal on June 21, 2015. Researchers found that this signal is a type of radio wave called a “whistler,” created when lightning emissions pass through a planet’s ionosphere.
This discovery indicates that electrical discharges do happen in Mars’ atmosphere. Interestingly, the way these radio waves travel through plasma follows similar principles to how lightning signals work on Earth.
Both Mars and Earth share some traits, but they have important differences. Take lightning, for example. On Earth, lightning forms when particles in the atmosphere collide, building up charge until it discharges. Typically, this occurs in moisture-rich clouds. Mars, however, has very little water in its atmosphere.
Fortunately, moisture isn’t necessary for lightning. On Earth, volcanic eruptions can also generate lightning. In fact, researchers recently found that electrical discharges on Mars likely come from sand particles being disturbed in its wild dust storms.
A “whistler” describes a specific type of electromagnetic signal emitted during lightning strikes. When lightning occurs, it sends out a wide range of electromagnetic waves. Some of the lowest-frequency waves can travel through the ionosphere as plasma waves along magnetic field lines. This creates a unique sound that resembles a descending tone, kind of like a whale’s call.
Mars doesn’t have a global magnetic field, making it seem unlikely for whistlers to thrive there. However, localized magnetic regions still exist, remnants from a time when Mars had a stronger magnetic field. Research from decades ago suggested that these crustal magnetic fields could enable whistlers to form.
MAVEN has been monitoring Mars since 2014, using various instruments to study the planet’s atmosphere. A team led by atmospheric physicist František Němec analyzed over 108,000 plasma wave recordings for whistler traits. Remarkably, they found one that matched earlier predictions.
This single whistler event occurred over a crustal magnetic field, 349 kilometers (217 miles) high, on Mars’ night side. This timing is crucial; during the day, Mars’ ionosphere is compressed, making plasma wave propagation difficult.
The whistler registered for about 0.4 seconds, sliding down in frequency, and was ten times stronger than the background noise. Researchers estimated that, considering signal loss during its journey, the energy at the source was comparable to a strong lightning strike on Earth.
Why haven’t more whistlers been detected? Only about 1% of plasma wave recordings were captured in conditions suitable for this type of signal. It requires an electric discharge, specific magnetic conditions, and the right instruments on a spacecraft passing by at just the right moment.
This suggests lightning may be more common on Mars than we realize. That’s thrilling for scientists. Some lab experiments indicate that electrical discharges can help form important organic molecules, a process that might have jumpstarted life on Earth. If similar discharges happen on Mars, it adds more considerations for scientists exploring past life possibilities on the red planet.
This fascinating research is documented in the journal Science Advances.
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