U.S. researchers believe they have answered a long-standing question about how electrons in the Earth’s Van Allen radiation belts can suddenly become energetic enough to kill orbiting satellites.
New observations by NASA’s twin Van Allen Probes show that particles in the radiation belts surrounding Earth are accelerated by a local kick of energy, helping to explain how these particles reach speeds of 99 percent the speed of light (G. Reeves / M. Henderson)
Since 1958, when space physicist Dr James A. Van Allen discovered the doughnut-shaped bands of intense radiation encircling the Earth, scientists have wondered just how and where electrons trapped within the belts get their ultra-high energies.
“Until the 1990s, we thought the Van Allen belts were pretty well-behaved and changed slowly. With more and more measurements, however, we realized how quickly and unpredictably the radiation belts change. They are basically never in equilibrium, but in a constant state of change,” said Dr Geoff Reeves from Los Alamos National Laboratory, lead author of a paper published in the journal Science.
Dr Reeves and his colleagues examined two possibilities: first, the long-accepted theory that the electrons get their energy as they make their way into the belts from outside them, or that they are accelerated inside the belts.
Using measurements from NASA’s twin Van Allen Probes, they determined that electrons gain their energy inside the belts.
“The Van Allen Probes data clearly eliminated the possibility of external electron acceleration and determined that electron acceleration is taking place through “local acceleration in the heart of the radiation belts,” said co-author Dr Craig Kletzing of the University of Iowa.
“We see case after case where the very high energy electrons appear suddenly right in the heart of the outer belt,” added study co-author Prof Daniel Baker from the Laboratory for Atmospheric and Space Physics.
“But now we can prove where the electrons originate from and we can see the waves – and the lower energy ‘seed’ particles – from which the relativistic electrons grow. We can essentially peer into the inner workings of our local cosmic accelerator with unprecedented clarity.”
Earlier this year, Van Allen Probes mission’s scientists reported the discovery of a previously unknown third radiation belt.
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Bibliographic information: Reeves GD et al. Electron Acceleration in the Heart of the Van Allen Radiation Belts. Science, published Online July 25, 2013; doi: 10.1126/science.1237743
