The Origin of Ultrafast Substorm Auroras

From time to time, sudden releases of energy in Earth’s magnetosphere lead to major disturbances that result in bright auroral displays over the planet’s polar regions. These auroras are caused by a phenomenon known as a geomagnetic substorm. The precise cause of these substorms has been debated for decades, but new computer simulations, allied to analysis of data from ESA’s Cluster spacecraft, are now filling in many of the missing pieces in the puzzle.