A moderate solar flare on May 17 lit up ground stations all over the world with an unexpected and puzzling pulse of high-energy particles. It should not have happened, and scientists are now trying to figure out why it did.
Major solar flares, flashes of light at various wavelengths often associated with coronal mass ejections (CMEs) are known to disrupt communications and can even trip power grids on Earth. But the May 17 flare was an M-class event, moderate and relatively common and not expected to create disturbances on the surface of Earth. Yet either the flare or the CME generated a ground-level enhancement (GLE), a blast of high-energy particles that lit up ground stations called neutron monitors on Earth for the first time in nearly six years.
Scientists don’t expect an M-class flare to create a GLE.