ESA's Mars orbiters watch solar superstorm hit the Red Planet

By Matthew Williams - March 12, 2026 09:43 PM UTC | Solar Astronomy
Images of the 2024 solar storm captured by NASA's Solar Dynamics Observatory's instruments, developed by the ESA/NASA. The bright spots to the right of the Sun are Jupiter and Venus. Credit: NASA/ESA
Images of the 2024 solar storm captured by NASA's Solar Dynamics Observatory's instruments, developed by the ESA/NASA. The bright spots to the right of the Sun are Jupiter and Venus. Credit: NASA/ESA

In May 2024, people worldwide witnessed beautiful aurorae that appeared far beyond Earth's polar regions. Even the Aurora Borealis, which is usually confined to the Arctic Circle, was visible as far south as Mexico. This rare event was the result of a massive solar storm, the most powerful recorded in over 20 years. As always, this storm bombarded Earth with charged solar particles that interacted with the planet's magnetosphere. The storm also reached Mars, which was witnessed by two orbiters operated by the European Space Agency (ESA) - the Mars Express and ExoMars Trace Gas Orbiter (TGO).

Working in tandem, the two spacecraft captured images of the event and obtained detailed information on the amount of radiation that reached Mars: the equivalent of 200 days of what is regularly exposed to in just 64 hours. The data was presented in a study published in Nature Communications, where an international team of researchers used a method pioneered by the ESA to reveal how this storm affected Mars. The results could lead to a better understanding of space weather and how solar storms interact with planets.

The technique is known as radio occultation, in which the Mars Express probe beamed a radio signal to the TGO as it disappeared over the Martian horizon. While the ESA routinely uses orbiter-to-orbiter radio occultation at Earth, this was one of the few instances in which it was used around Mars. Basically, the radio signal was refracted by layers in Mars' atmosphere before being picked up by TGO, allowing scientists to learn more about each layer. Data from NASA's Mars Atmosphere and Volatile Evolution (MAVEN) mission was also used to confirm the electron densities.

To study Mars’s atmosphere, ESA’s two Mars orbiters make use of a technique called ‘radio occultation.’ Credit:ESA *To study Mars’s atmosphere, ESA’s two Mars orbiters make use of a technique called ‘radio occultation.’ Credit:ESA*

Colin Wilson, an ESA project scientist for Mars Express and TGO and a co-author of the study, said in an ESA press release:

This technique has actually been used for decades to explore the Solar System, but using signals beamed from a spacecraft to Earth. It’s only in the past five years or so that we’ve started using it at Mars between two spacecraft, such as Mars Express and TGO, which usually use those radios to beam data between orbiters and rovers. It’s great to see it in action.

The superstorm coincided with the hyperactive sunspot region AR3664 returning to the Sun's Earth-facing side. The blast sent out a class X2.9 flare and a large cloud of material - aka. a Coronal Mass Ejection (CME) - towards Earth and Mars. On Mars, the storm caused a dramatic increase in electrons in two layers of its atmosphere - 110 and 130 km (68 and 80 mi) above the surface - of 45% and 278% (respectively), the most electrons that have ever been observed in this region of the Martian atmosphere. Said ESA Research Fellow Jacob Parrott, the lead author of the study:

The impact was remarkable: Mars’s upper atmosphere was flooded by electrons. It was the biggest response to a solar storm we’ve ever seen at Mars. 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. Luckily, the spacecraft were designed with this in mind, and built with radiation-resistant components and specific systems for detecting and fixing these errors. They recovered fast.

ESA's Swarm satellites map Earth's magnetic field as it is warped by the solar storm of May 2024. Credit: ESA *ESA's Swarm satellites map Earth's magnetic field as it is warped by the solar storm of May 2024. Credit: ESA*

Thanks to Earth's magnetosphere, the response of the upper atmosphere was less intense, with much of the storm's particles deflected away from the planet or diverted toward the poles (causing the aurorae). This highlights the differences between our planets and also demonstrates the importance of studying how space weather impacts different bodies in the Solar System. Since solar storms can endanger astronauts and equipment in orbit, as well as disrupt satellites and electrical grids on the surface, space weather forecasting is of vital importance.

This is difficult, however, as the Sun emits solar flares and CMEs unpredictably, making studying them a matter of luck and timing. Fortunately, the team was able to use the new technique just 10 minutes after the solar storm reached Mars. In total, the team captured the aftermath of three solar events that were part of the same storm but differed in the type of material ejected and the way it was done. This included a flare of radiation, a burst of high-energy particles, and a CME. Said Colin:

The results improve our understanding of Mars by revealing how solar storms deposit energy and particles into Mars’s 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. But there’s another side to it: the structure and contents of a planet’s atmosphere influence how radio signals travel through space. 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.

Further Reading: ESA

Matthew Williams

Matthew Williams

Matt Williams is a space journalist, science communicator, and author with several published titles and studies. His work is featured in The Ross 248 Project and Interstellar Travel edited by NASA alumni Les Johnson and Ken Roy. He also hosts the podcast series Stories from Space at ITSP Magazine. He lives in beautiful British Columbia with his wife and family. For more information, check out his website.