Solar flares are sometimes associated with events called coronal mass ejections (CMEs), explosions in which billions of charged particles are blasted into space at high speed. NASA has detected a CME in this case, which it says it is traveling toward Earth at almost 1,400 miles per second.
A CME can disturb the Earth's magnetosphere – the magnetic "envelope" that surrounds the planet and protects us from most of the Sun's radiation. Depending on the direction from which solar magnetic energy arrives, it can interact strongly with the oppositely oriented magnetic field of the Earth, NASA says, causing Earth's field to be "peeled open like an onion." That allows charged particles to stream into Earth's atmosphere and rain down along magnetic field lines, which is known as a geomagnetic storm.