Featured Science Paper
Plasma Astrophysics, Acceleration of killer electrons
High energy electrons in the outer Van Allen radiation belt wreak havoc with satellites in geostationary orbit, but how they are accelerated to such high energies has been unclear. Now research recently published in Nature Physics by BAS scientist Dr Richard Horne suggests a new model new for producing these highly damaging electrons.
Since the early 1960s it was thought that electrons originating from the Sun would become trapped inside the Earth’s magnetic field and be accelerated as they were transported towards the Earth. Eventually they would be lost to the atmosphere. However, over the last 10 years, BAS scientists have been proposing that a special type of very low frequency radio waves inside the Earth’s magnetic field do the accelerating. New evidence from multiple spacecraft now supports this idea and has prompted a new model.
The key element is that radio waves accelerate the electrons inside the Earth’s magnetic field. The accelerated electrons are then transported both inwards and outwards to fill up the entire outer Van Allen radiation belt (see Figure). The waves are excited by a distribution of much lower energy electrons, which still originate from the Sun, but become unstable as they penetrate closer to the Earth.
High energy electrons are also known as killer electrons since they cause radiation damage to satellites. In 2003, during Halloween, more than 30 satellites reported malfunctions and one was a total failure during a period when the Van Allen radiation belts were drained and then reformed much closer to the Earth. A modern telecommunications satellite costs about US$ 250M to build, $100M to launch into geostationary orbit, and annual insurance premiums are around 3% of the sum insured. With more than 300 satellites in geostationary orbit alone, and a growing reliance on satellite technology, understanding radiation belt dynamics should help us to protect our investment and manage the risks involved.
Dr Richard B Horne
Horne, R. B., Nature Physics, 3, 590-591, doi:10.1038/nphys703 September (2007)