SOLAR STORM BATTERS MARS

Revealing atmospheric vulnerability

In May 2024, the Sun unleashed the most intense solar storm to strike Earth in more than two decades. Triggered by an unusually active region on the Sun’s surface, the event comprised a series of powerful solar flares and coronal mass ejections that hurled magnetised plasma across the Solar System. On Earth, the effects were both striking and disruptive: auroras were seen as far south as Mexico, while satellites and systems experienced disturbances. New data now show that the impact on Mars was even more pronounced.

ESA’s two Mars orbiters, Mars Express and the ExoMars Trace Gas Orbiter (TGO), were well placed to observe the event. The TGO’s radiation monitor recorded a dose equivalent to around 200 ‘normal’ days in just 64 hours. The surge of high-energy particles caused temporary computer glitches on both spacecraft, although their radiation-hardened systems ensured a rapid recovery.

The scientific impact was equally significant. The Red Planet’s upper atmosphere was flooded with energetic electrons. Using radio occultation, in which Mars Express transmits a signal to TGO through the Martian atmosphere, scientists measured increases in electron density of 45 per cent at an altitude of 110 kilometres and 278 per cent at 130 kilometres. These are the highest values recorded at these heights.

The storm highlights the contrast between Earth and Mars. Earth’s global magnetic field acts as a shield, deflecting most charged particles, whereas Mars lacks such protection. This vulnerability has contributed to the long-term loss of its atmosphere and water to the solar wind. Elevated electron densities can also interfere with radio signals, posing challenges for future missions and surface operations. The May 2024 event therefore provides a valuable opportunity to study how planetary atmospheres respond to extreme solar activity.

As solar activity continues to rise towards the peak of the current cycle, such storms are expected to become more frequent. ESA is expanding its space-weather monitoring fleet: current missions such as SOHO (Solar and Heliospheric Observatory) and Solar Orbiter will be joined by SMILE (Solar wind Magnetosphere Ionosphere Link Explorer), which at the time of writing is scheduled for launch on 9 April 2026. By 2031, the Vigil mission aims to provide continuous monitoring from deep space, offering up to five days’ warning of potentially hazardous solar events.

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doi.org/10.1038/s41467-026-69468-z

doi.org/10.1016/j.lssr.2025.02.010