Solar explosions: how the Sun can knock out satellites, GPS and the power grid

The name of this portal is no accident. Solar explosions are among the most violent phenomena in the Solar System: in a matter of minutes, a single eruption releases energy equivalent to billions of atomic bombs. Most of the time, this spectacle occurs about 150 million kilometres away with no impact on us. But when the eruption points toward Earth, its effects can be felt on satellites, on a cell phone’s GPS signal, and even on the power grid that lights our cities.

Understanding this phenomenon is no longer the exclusive domain of astronomers. Modern life relies on a space and electrical infrastructure increasingly vulnerable to the Sun’s temperament — and that is why space agencies, energy operators and governments treat so-called space weather as a strategic issue.

What a solar explosion actually is

The Sun is a rotating sphere of plasma threaded by magnetic fields that twist and coil like elastic bands. Where the field is strongest, sunspots appear—dark areas that act as reservoirs of magnetic energy. When the field lines snap and reconnect abruptly, that energy is released at once: a solar explosion, or flare, is born.

The explosion emits radiation ranging from X-rays to visible light, traveling at light speed and reaching Earth in about eight minutes. Scientists classify flares into increasing intensity categories—A, B, C, M and X—each letter representing a ten-fold jump in power. An X-class flare, the top of the scale, can cause immediate radio blackouts on the sunlit side of the planet.

But the flare is usually only the first act. The strongest eruptions are accompanied by a coronal mass ejection: billions of tons of magnetized plasma hurled into space at millions of kilometres per hour. This cloud takes one to three days to reach Earth—and is the primary driver of geomagnetic storms.

Geomagnetic storm: when Earth’s shield is shaken

Earth is protected by an invisible shield, the magnetosphere, generated by the movement of liquid iron in the planet’s core. When a coronal mass ejection collides with this shield, the magnetosphere is compressed and shaken, inducing electric currents in the upper atmosphere and in the ground itself—it is the geomagnetic storm, classified from G1 (weak) to G5 (extreme).

The most beautiful effect of this collision is the auroras: accelerated particles plunge into the atmosphere, making the sky glow green and red. Normally confined to polar regions, severe storms push them to much lower latitudes. That’s what happened in May 2024, when the most intense storm in about two decades painted the sky red in unlikely places—including sightings as far south as Brazil, an extremely rare occurrence.

Lessons from history: from 1859 to the Quebec blackout

The most extreme case on record occurred in 1859, the so-called Carrington Event. Electrical technology at the time was limited to the telegraph—and even then chaos ensued: lines sparked, operators received shocks, and auroras were seen in tropical regions. Studies estimate that an event of that magnitude would today cause global losses in the trillions of dollars.

In March 1989, a severe storm knocked out Quebec’s power grid in minutes, leaving millions without electricity for about nine hours in the middle of winter. In 2003, the Halloween storms damaged satellites and forced reroutes of polar air traffic. And in 2022, dozens of newly launched Starlink satellites failed because a moderate storm expanded the upper atmosphere and increased drag on them.

Satellites, GPS and the power grid: the three main targets

Satellites

Energetic particles can penetrate electronic circuits, corrupt memory, shut down systems, or permanently damage components. Moreover, the storm-heated atmosphere expands, increasing drag on low-orbit satellites, shortening their operational life or de-orbiting them.

GPS and navigation

GPS signals must pass through the ionosphere, an electrified layer of the upper atmosphere. During storms, this layer becomes turbulent, causing scintillation: the signal arrives distorted or disappears entirely. Positioning error can jump from centimeters to tens of metres—a serious issue for aviation, maritime navigation, oil platforms, and precision agriculture, which relies on centimetre-level corrections for planting and harvesting.

Power grid

Storms induce so-called geomagnetically induced currents in the ground, which enter the grid through grounding points. High-voltage transformers, designed for alternating current, then receive a quasi-continuous current that saturates and overheats them. In the worst case, giant transformers—costing millions and taking months to replace—suffer permanent damage, turning a power outage lasting hours into a weeks-long crisis.

And what about Brazil in all this?

Brazil has a particular relationship with space weather. Part of its territory lies beneath the South Atlantic Magnetic Anomaly, a region where Earth’s magnetic field is weaker. Satellites passing over this area receive higher radiation doses—so much so that many switch off sensitive instruments when crossing it.

Moreover, being in the equatorial belt, the country chronically suffers from ionospheric scintillation, which degrades GPS on certain nights even without any storm. Not coincidentally, the National Institute for Space Research runs Embrace, a program that monitors the ionosphere and magnetic field over South America in real time. Add to that a continent-wide interconnected power system, with transmission lines stretching thousands of kilometres—exactly the type of structure that acts as an antenna for induced currents.

Can it be forecasted?

Yes, albeit with limits. Space observatories monitor the Sun around the clock and can see sunspots growing days before any eruption. The flare itself gives no warning—its radiation arrives together with the light—but the coronal mass ejection, the most dangerous, takes one to three days to reach Earth. This window allows concrete actions: power-grid operators redistribute load and protect transformers, satellites enter safe mode, airlines adjust routes, and agencies issue navigation alerts.

Solar activity follows an approximately 11-year cycle, alternating calm and active periods. At cycle maxima, flares and ejections become much more frequent—and the probability of an extreme event rises.

A rare risk that grows with our dependence

The Sun hasn’t changed: storms like the 1859 event have always occurred and will happen again. What has changed is us. In a century and a half, we have moved from the telegraph to a civilization hanging on satellites, GPS and interconnected power grids. The good news is that, unlike an earthquake, a major solar storm gives advance notice that it is on its way. The challenge is to ensure that, when the warning arrives, satellites, grids and governments know exactly what to do. Monitoring our star is no longer a scientific curiosity: it is a matter of life-support for modern infrastructure—and it is also the mission that gives this portal its name.