Peking University. Beijing. March 20, 2010: Prof. Zong Qiugang and his colleagues from Peking University have discovered the origin of killer electrons in the earth’s magnetosphere. The work has been published in the Journal of Geophysical Research-Space Physics and introduced to public and scientific societies by European Space Agency (ESA) as headlines on its websites.
Take a bunch of fast-moving electrons, place them in orbit and then hit them with the shock waves from a solar storm. What do you get? Killer electrons. Killer electrons are highly energetic particles tracked in Earth’s outer radiation belt which extends from 12000 to 64000 km above the planet’s surface. During solar storms their number grows at least 10 times and they can be dislodged, posing a threat to satellites. As the name suggests, the electrons are energetic enough to penetrate the satellite’s shielding and cause microscopic lightning strikes. If these electrical discharges take place in vital components, the satellite will be damaged or even rendered inoperable.
Understanding the origin of the killer electrons has been a mission for space weather researchers. Two mechanisms have been proposed by scientists to explain how the electrons can be accelerated to such harmful energy levels. One relies on very low frequency (VLF) waves of 3—30 kHz, the other on ultra low frequency (ULF) waves of 0.001—1 Hz. However, which kind of waves is responsible was unclear until Professor Zong and his colleagues disentangled it. Their study has shown that both VLF and ULF waves accelerate electrons in Earth’s radiation belts, but with different timescales. A two-step process causes the substantial rise of killer electrons. The initial acceleration is due to the strong shock-related magnetic field compression. Immediately after the impact of the interplanetary shock, Earth’s magnetic field lines began wobbling at ultra low frequencies. In turn, these ULF waves were found to effectively accelerate the seed electrons provided by the first step, to become killer electrons. “Data from the four Cluster satellites allowed the identification of ULF waves able to accelerate electrons,” says Malcolm Dunlop, Rutherford Appleton Laboratory, Didcot (UK) and co-author of this study. Philippe Escoubet, ESA’s Cluster mission manager, commented “these new findings help to improve the models predicting the radiation environment in which satellites and astronauts operate. With solar activity now ramping up, we expect more of these shocks to impact our magnetosphere over the months and years to come.”
For more information, see the paper below:
Zong, Q.-G., X.-Z. Zhou, Y. F. Wang, X. Li, P. Song, D. N. Baker, T. A. Fritz, P. W. Daly, M. Dunlop, and A. Pedersen (2009), Energetic electron response to ULF waves induced by interplanetary shocks in the outer radiation belt, J. Geophys. Res., 114, A10204, doi:10.1029/2009JA014393.
You can also find more information on ESA’ websites:
For public:
http://www.esa.int/esaSC/SEM8DL9KF6G_index_0.html
For professionals:
http://sci.esa.int/science-e/www/object/index.cfm?fobjectid="46685
Edited by: Connie Chang
Translated by: HAN Yafei
Source: PKU News (Chinese)
