Mars Atmosphere Swells to Record Levels During Solar Superstorm

Cosmic Lightning Hits Mars

When the largest solar storm in over two decades slammed into Mars in May 2024, the Red Planet's atmosphere responded in ways scientists had never witnessed before. The superstorm caused a dramatic increase in electrons in two distinct layers of Mars's atmosphere at altitudes of around 110 and 130 km, with numbers rising by 45% and a whopping 278%, respectively. This is the most electrons we've ever seen in this layer of martian atmosphere.

The impact was remarkable: Mars's upper atmosphere was flooded by electrons , explained ESA Research Fellow Jacob Parrott, lead author of the groundbreaking study published in Nature Communications. It was the biggest response to a solar storm we've ever seen at Mars. The same storm that triggered auroras visible as far south as Mexico on Earth created an entirely different spectacle on our neighboring planet.

Two European Space Agency orbiters, Mars Express and the ExoMars Trace Gas Orbiter, happened to be perfectly positioned when the cosmic bombardment arrived. A radiation monitor aboard TGO picking up a dose equivalent to 200 'normal' days in just 64 hours. The timing was extraordinary—scientists rarely get such clear observations of how solar storms affect other worlds.

Technology Under Fire

The solar assault didn't just transform Mars' atmosphere; it also wreaked havoc on the spacecraft studying it. The storm also caused computer errors for both orbiters – a typical peril of space weather, as the particles involved are so energetic and hard to predict , Parrott noted. Fortunately, both spacecraft recovered quickly thanks to their radiation-resistant designs and built-in error correction systems.

To capture this unprecedented event, researchers used an innovative technique called mutual radio occultation. Mars Express beamed a radio signal to TGO at the very moment it was disappearing over the Martian horizon. As TGO vanished, the radio signal was bent ("refracted") by the various layers of Mars's atmosphere before being picked up by the orbiter, allowing scientists to glean more about each layer. This method, pioneered by ESA for interplanetary use, works like shining a flashlight through fog to measure its density.

The technique revealed how solar plasma and X-rays collided with neutral atoms in Mars's upper atmosphere and stripped away their electrons, boosting the number of free electrons and charged particles. Unlike Earth, which enjoys protection from its magnetic field, Mars stands naked against the solar wind.

Planetary Differences Revealed

The superstorm was experienced very differently at Earth and Mars, highlighting the differences between the two worlds. At Earth, the response of the upper atmosphere was more muted, thanks to the shielding effect of Earth's magnetic field. While Earth's magnetosphere deflected much of the storm and channeled particles toward the poles to create beautiful auroras, Mars absorbed the full brunt of the cosmic assault.

This vulnerability helps explain Mars' current barren state. The results improve our understanding of Mars by revealing how solar storms deposit energy and particles into Mars' atmosphere — important as we know the planet has lost both huge amounts of water and most of its atmosphere to space, most likely driven by the continual wind of particles streaming out from the sun , noted Colin Wilson, ESA project scientist for both Mars missions.

Future Mission Planning

The findings carry practical implications for future Mars exploration. If Mars's upper atmosphere is packed full of electrons, this could block the signals we use to explore the planet's surface via radar, making it a key consideration in our mission planning—and impacting our ability to investigate other worlds. Mission planners will need to account for these atmospheric disruptions when designing future robotic missions and eventual human expeditions.

As space agencies prepare for more ambitious Mars missions, understanding how solar storms affect the planet becomes crucial for both equipment protection and communication reliability. The May 2024 superstorm provided an invaluable natural experiment, offering insights that could prove essential for the next generation of Mars explorers—whether robotic or human.