Between Jan. 15 and 20, a single collection of sunspots erupted seven times. Four of these events hurled into space powerful X-ray–emitting flares accompanied by billion-ton clouds of charged particles. The eruptions themselves weren't record breakers, but one was accompanied by a storm of high-energy protons that was the most energetic proton squall that's been recorded near Earth in 15 years.
The storm, detected by a weather satellite within minutes of a Jan. 20 solar flare, was particularly rich in protons packing more than 100 million electron-volts (MeV) of energy. Protons of this energy can burrow through 11 centimeters of water.