A once-in-century solar storm could fry power grids and knock out satellites. On rare occasions, the sun will send a storm so powerful it can tear open the Earth’s magnetic fields.

If such a storm hit tomorrow, it would cause technological chaos that could “cripple economies and endanger the safety and livelihoods of people worldwide,” according to NASA (National Aeronautics and Space Administration.)

These storms are very rare, but the sun is getting restless ahead of a 20-year peak of activity, meaning there’s more of a chance one could come to Earth in coming years, experts told Business Insider. Three different solar events can all send high-speed particles that mess with the Earth’s magnetic fields: solar flares, coronal holes, or coronal mass ejections (CMEs) — huge explosions on the sun.

If any of these types of solar storms happen to impact the Earth with enough force, they can peel back the Earth’s ionized layer which protects us against the worst of space weather. This can open the door for more charged particles to pour through and harm or take down power grids across the globe.

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“We’re talking a one-in-a-hundred-year event,” Mathew Owens, a professor of space physics at the University of Reading, told Business Insider.

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These kinds of intense geomagnetic storms can happen at any time, but they become much more likely during a peak of solar activity, which happens about every 11 years when the sun’s magnetic field lines get more knotted. All of that tension increases the chance the sun will create more sunspots, more CMEs, more solar flares, and more coronal holes. All of this gives more opportunity for a “once-a-century event” to arise

We’ve gotten several solar storm warnings over the past decade, however, with constant news that the power grid is overwhelmed, at some point, we could actually see it go down.