September 24, 2013
New Insight Into Origins Of Mysterious Radiation Belt
John P. Millis, PhD for redOrbit.com - Your Universe Online
[ Watch the Video: Ultra-fast Electrons Explain Third Radiation Belt ]
At the dawn of the space race, as two global powers jockeyed for technological supremacy, the ultimate goal was to be the first to send astronauts into space and onto the Moon. While space exploration is rife with challenges, one hurdle in particular brought into question whether man would ever leave low Earth orbit: the Van Allen radiation belts.
These belts, first discovered in 1958, consist of two doughnut-shaped rings where high-energy charged particles and ions are trapped by Earth’s magnetic field. Because of their high velocity, these charged particles give off significant radiation and can also penetrate through shielding on spacecraft.
Not only is this radiation troubling for humans passing through the rings, but also for normal satellites with their sensitive electronics. As a result, researchers study these rings in an attempt to understand their origins, dynamics, and evolution in order to combat their effects.
The geometry of the belts can best be described as two individual rings. The first is the inner ring dominated by streams of high-energy electrons and fast moving ions, while the outer ring contains almost exclusively high-energy electrons. But in a startling discovery, a third, middle ring appeared in September 2012, and persisted for about a month.
Since then, scientists have been attempting to explain how this new ring was created. Now, a new study published in the September 22 issue of the journal Nature Physics has modeled the creation and evolution of this new belt.
"In the past, scientists thought that all the electrons in the radiation belts around the Earth obeyed the same physics," said Yuri Shprits, a research geophysicist with the UCLA Department of Earth and Space Sciences, in a statement. "We are finding now that radiation belts consist of different populations that are driven by very different physical processes."
The dominating particle population of the shortly lived belt was found to be ultra-high energy electrons, not dissimilar to the most energetic leptons in the other belts.
"Their velocity is very close to the speed of light, and the energy of their motion is several times larger than the energy contained in their mass when they are at rest," Kellerman said. "The distinction between the behavior of the ultra-relativistic electrons and those at lower energies was key to this study."
The key result of this study was the finding that plasma waves produced by ions, which ordinarily affect the electron population, "whipped out ultra-relativistic electrons in the outer belt almost down to the inner edge of the outer belt."
"This study shows that completely different populations of particles exist in space that change on different timescales, are driven by different physics and show very different spatial structures," Shprits said.
"We have a remarkable agreement between our model and observations, both encompassing a wide range of energies," said Dmitriy Subbotin, a former graduate student of Shprits and current UCLA staff research associate.
There are, of course, broader implications to this work. Understanding the fundamental interactions taking place at this energy scale is critical to understanding the evolution of the radiation belts.
"I believe that, with this study, we have uncovered the tip of the iceberg," Shprits said. "We still need to fully understand how these electrons are accelerated, where they originate and how the dynamics of the belts is different for different storms."