In the vast silence between planets, a storm of particles can travel like a ripple across an unseen ocean — only perceptible when it meets something in its path. Our Sun, a roiling sphere of heat and magnetic motion, occasionally sends such ripples outward, and when they reach a world like Mars, they can paint a picture of cosmic force and fragile atmosphere. In a stroke of cosmic serendipity, orbiting spacecraft watched just such an event unfold at Mars, revealing new details about how powerful solar storms batter worlds beyond our own.
On a quiet day in May 2024, the Sun unleashed one of the most intense solar storms seen in decades. This superstorm — a furious combination of solar radiation, high‑energy particles, and coronal mass ejections — first swept past Earth, lighting skies and unsettling satellites. But it did not stop there. Mars, farther out in the solar system and without a protective global magnetic field like Earth’s, bore the brunt of this wave of charged particles as it continued outward.
Two European Space Agency orbiters — Mars Express and the ExoMars Trace Gas Orbiter (TGO) — were in the right place at the right time to witness the encounter. Their instruments, designed to peer into the tenuous layers of the Martian atmosphere, registered an influx of radiation equivalent to roughly 200 times a normal daily dose over just 64 hours, a testament to the storm’s strength. Because these spacecraft only conduct detailed atmospheric observations twice a week, this remarkable dataset was collected during a rare observational window, a moment scientists now describe as extremely lucky.
As the superstorm engulfed Mars, electrons flooded its upper atmosphere, increasing their density by roughly 45 % in one layer and nearly 280 % in another — the most such particles ever recorded in those regions. These charged particles were stripped from neutral atoms as the storm’s energetic plasma collided with the atmosphere, illuminating how space weather deposits energy into a planet’s outermost shells.
Such dramatic atmospheric responses are muted on Earth by our planet’s magnetic shield, which diverts many charged particles toward the poles and protects the bulk of the atmosphere. Mars, lacking such a global magnetosphere, offers scientists a clearer — though harsher — view of the Sun’s raw influence. The different reactions of the two planets to the same storm enrich researchers’ understanding of both worlds and the varying effects of space weather.
The orbiters themselves also felt the storm’s effects. Both spacecraft experienced temporary computer glitches as energetic particles struck sensitive electronics, a reminder that space weather is not just an academic curiosity but an active concern for mission designers and operators. Built with radiation‑resistant systems and recovery protocols, the orbiters weathered these disturbances without lasting harm.
To probe the atmospheric changes, scientists used a technique called radio occultation — one spacecraft beams a signal through the atmosphere to the other as the planet blocks its line of sight. Changes in the signal reveal details about atmospheric composition and density, allowing teams to map how the storm reshaped Mars’s upper layers within minutes of the solar flare’s arrival.
This rare alignment of storm and observation offers scientists a treasure trove of data to explore how solar activity sculpts planetary atmospheres across the solar system. By comparing Mars’s response with Earth’s, researchers hope to refine models of atmospheric loss, magnetic shielding, and how stellar winds influence planetary evolution.
In straightforward scientific terms, researchers report that ESA’s Mars Express and ExoMars Trace Gas Orbiter captured detailed observations of a powerful solar superstorm’s impact on Mars’s upper atmosphere, revealing unprecedented electron density increases and offering insights into space weather effects on planets without protective global magnetic fields.
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