Where did the killer electrons go?

Geomagnetic storms caused by energetic eruptions from the Sun can drive streams of high-energy electrons that travel close to the speed of light through the Van Allen radiation belts that encircle the Earth. These 'killer electrons' can play havoc with telecommunications satellites in geosynchronous orbit. But sometimes a geomagnetic storm can have the opposite effect, causing the electron flux to fall dramatically, by many orders of magnitude in just a few hours. Until now, no-one knew where these killer electrons were disappearing to. Now, using data collected at many different altitudes above the Earth, researchers report online in Nature Physics this week that they may have found the answer. To solve the mystery, Drew Turner and colleagues analysed data collected during a geomagnetic storm that took place on 6 January 2011. This involved a total of 11 independent satellites and spacecraft — from the THEMIS (Time History of Events and Macroscale Interactions during Substorms), GOES (Geostationary Operational Environmental Satellite), and POES (Polar Operational Environmental Satellite) missions — run variously by NASA, the National Oceanic and Atmospheric Administration and the European Organization for the Exploitation of Meteorological Satellites. The researchers found that during this event, the flux of high-energy electrons in the outer Van Allen radiation belt was directed out of the belt away from the Earth, being lost into outer space, rather than inward towards the Earth's atmosphere as suggested by some explanations of the loss.