On 28 October 2003, a large group of sunspots in the Sun’s southern hemisphere erupted, producing an intense x-ray flare and a large, fast coronal mass ejection (CME). That solar flare, like many others, released on a time scale of minutes as much as 1025 joules of electromagnetic energy—roughly equivalent to all the energy stored in fossil fuels on Earth, or 10 million times as much energy as that released from a volcanic explosion. Surprisingly, up to 50% of that energy can appear as accelerated electrons. Flares also accelerate ions near the Sun to energies greater than 100 MeV.
The day after the October solar event, the CME slammed into Earth’s magnetic field and triggered a powerful geomagnetic storm during which electrons were accelerated to relativistic energies inside Earth’s radiation belts. Strong, geomagnetically induced currents over northern Europe caused the electrical grid to fail, which triggered a subsequent...
