Attack of the killer electrons

What do you get if you smash fast-moving electrons in orbit with shock waves from a solar storm? Killer electrons, according to the European Space Agency’s Cluster mission.

But this is no joke: these killer electrons – highly energetic particles trapped in the Earth’s outer radiation belt – can penetrate satellite shielding and cause damage, or even render them inoperable. Understanding their origin has been at the forefront of space weather researchers’ minds.

Data from Cluster – a European Space Agency (ESA) unmanned space mission to the Earth’s magnetosphere – and other space missions suggests two types of wave accelerate electrons: ultra low frequency (ULF) waves of 0.0001-1 Hz and very low frequency (VLF) waves of 3-30 kHz

“Both VLF and ULF waves accelerate electrons in the Earth’s radiation belts, but with different timescales,” said Qiugang Zong, lead author of study, “The ULF waves are much faster than the VLF, due to their much larger amplitudes.”

Scientists examined data from Cluster’s four satellites following a solar storm in November 2004. The storm was composed of an interplanetary shock wave followed by a large magnetic cloud. Scientists discovered a two step process for accelerating electrons.

The initial acceleration was due to the strong shock-related magnetic field compression which swept over the satellite as the solar wind increased. When the shock wave hit the magnetosphere, the impact caused a wave front inside the magnetosphere. The Earth’s magnetic field lines began ‘wobbling’ at ultra low frequencies, and these ULF waves accelerated seed electrons to become killer electrons.

“These new finding help us to improve the models predicting the radiation environment in which satellites and astronauts operate,” said Philippe Escoubet, ESA’s Cluster mission manager, “With solar activity now ramping up, we expect more of these shocks to impact our magnetosphere over the months and years to come.”