The Red Planet recently experienced a significant atmospheric event triggered by a powerful solar storm that also impacted Earth in May 2024. Thanks to the European Space Agency’s (ESA) Mars Express and ExoMars Trace Gas Orbiter (TGO), scientists have gained valuable insights into how such events affect the Martian environment – and the spacecraft themselves. The storm, the largest recorded in over two decades, caused disruptions to both orbiters although simultaneously supercharging the upper Martian atmosphere.
The solar storm, which sent shimmering auroras as far south as Mexico on Earth, also delivered a substantial dose of radiation to Mars. The radiation monitor aboard TGO registered a level equivalent to 200 “normal” days in just 64 hours, highlighting the intensity of the event. A new study published in Nature Communications details the extent of the storm’s impact on Mars, revealing a dramatic increase in electron density and temporary operational challenges for the orbiting spacecraft.
Electron Surge in the Martian Atmosphere
“The impact was remarkable: Mars’s upper atmosphere was flooded by electrons,” explained ESA Research Fellow Jacob Parrott, lead author of the study. “It was the biggest response to a solar storm we’ve ever seen at Mars.” The superstorm led to a significant increase in electrons in two distinct layers of the Martian atmosphere, at altitudes of approximately 110 and 130 kilometers. Electron counts rose by 45% in the lower layer and a substantial 278% in the higher layer, representing the highest electron densities ever observed in that region of the Martian atmosphere.
The storm wasn’t without its challenges for the ESA orbiters. “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 added. Fortunately, both Mars Express and TGO were designed with radiation-resistant components and systems for detecting and correcting errors, allowing them to recover quickly.
Pioneering Radio Occultation Techniques
To investigate the storm’s effects, Parrott and his team employed a technique called radio occultation, currently being refined by ESA. This method involves beaming a radio signal from Mars Express to TGO as TGO passes over the Martian horizon. As the signal is bent, or refracted, by the various layers of the atmosphere, scientists can glean information about each layer’s composition and density. Observations from NASA’s MAVEN mission were also used to confirm the electron densities measured by the ESA orbiters. ESA details the radio occultation technique here.
“This technique has actually been used for decades to explore the Solar System, but using signals beamed from a spacecraft to Earth,” said Colin Wilson, ESA project scientist for Mars Express and TGO, and co-author of the study. “It’s only in the past five years or so that we’ve started using it at Mars between two spacecraft.” ESA routinely uses orbiter-to-orbiter radio occultation at Earth and plans to expand its use in future planetary missions.
Different Atmospheres, Different Responses
The impact of the solar storm differed significantly between Earth and Mars, largely due to the presence of Earth’s protective magnetic field. While Earth’s magnetic field deflected much of the incoming solar radiation, it also channeled some particles towards the poles, creating the spectacular auroral displays. Mars, lacking a global magnetic field, is more directly exposed to solar activity.
Understanding how solar activity impacts planetary atmospheres is crucial for space weather forecasting. Solar storms can pose risks to astronauts and equipment in space, and can disrupt satellite systems and terrestrial infrastructure, including power grids and navigation systems. Studying these events is challenging due to the unpredictable nature of the Sun, but the fortuitous timing of the May 2024 storm allowed for a unique opportunity to gather data.
“Fortunately, we were able to use this new technique with Mars Express and TGO just 10 minutes after a large solar flare hit Mars,” Parrott explained. “Currently we’re only performing two observations per week at Mars, so the timing was extremely lucky.” The team analyzed data from three distinct solar events – a radiation flare, a burst of high-energy particles, and a coronal mass ejection (CME) – all part of the same larger storm.
The results of the study enhance our understanding of how solar storms deposit energy and particles into the Martian atmosphere, a factor believed to have contributed to the planet’s loss of water and atmosphere over billions of years. The increased electron density in the Martian atmosphere could impact future radar-based investigations of the planet’s surface. “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,” Wilson noted.
ESA is actively monitoring the Sun with missions like Solar Orbiter, which continuously observes our star, and is preparing to launch additional missions, including Smile (scheduled for 2026) and Vigil (planned for 2031), to improve space weather forecasting capabilities. Learn more about ESA’s Solar Orbiter mission here.
The study, “Martian ionospheric response during the May 2024 solar superstorm,” by J. Parrott et al., was published in Nature Communications. DOI: 10.1038/s41467-026-69468-z
As ESA and NASA continue to collaborate on Mars exploration, understanding the impact of space weather events will be critical for ensuring the success of future missions and protecting both robotic and, eventually, human explorers on the Red Planet. Further research utilizing advanced techniques like radio occultation will undoubtedly refine our understanding of the complex interactions between the Sun and Mars.
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