December 4, 2013
Earth’s Van Allen Belts Thrust Particles To Near The Speed Of Light
Lee Rannals for redOrbit.com - Your Universe Online
NASA’s twin Van Allen Probes have led to another new discovery of Earth’s mysterious radiation belts.
Researchers used data from the NASA spacecraft to reveal that the high-energy particles populating the Van Allen radiation belts can be accelerated to nearly the speed of light. This finding comes on the heels of a related discovery showing similar particle acceleration but on a microscopic, rather than planetary, scale.
“The acceleration we first reported operates on the scale size of an electron’s gyromotion—it is a really local process, maybe only a few hundred meters in size,” Harlan Spence, director of the University of New Hampshire Institute for the Study of Earth, Oceans, and Space and coauthor on the Nature Communications paper, said in a statement. “Now we’re seeing this large-scale, global motion involving ultra low-frequency waves pulsing through Earth’s magnetosphere and operating across vast distances up to hundreds of thousands of kilometers.”
Having the probes make simultaneous measurements in different regions of nearby space is a key aspect of the mission, allowing scientists to look at data separated by both space and time.
“With the Van Allen Probes, I like to think there’s no place for these particles to hide because each spacecraft is spinning and ‘glimpses’ the entire sky with its detector ‘eyes’, so we’re essentially getting a 360-degree view in terms of direction, position, energy, and time,” Spence said.
Ian Mann, from the University of Alberta and first author of the paper, said people have considered this acceleration process might be present but they haven’t been able to see it clearly until now, with the advent of the Van Allen Probes mission.
The action described by the researchers is analogous to that of a particle accelerator like the Large Hadron Collider. However, with the Van Allen Belts, the Earth’s vast magnetic field revs up drifting electrons to ever-higher speeds as they circle the planet.
"Essentially near-Earth space is filled with a basic magnetic field which can be perturbed by a modest solar wind from a very typical star," Mann said. "When compared with the much more exotic astrophysical objects out in the universe, Earth's system doesn't initially look like it should accelerate particles up to such incredible speeds. But something is happening right above our heads that is a very efficient, planetary-scale accelerator, and scientists have been trying to understand this ever since the belts were first discovered."
Better understanding of the processes inside the belts can ultimately help protect orbiting spacecraft from damage. The radiation belts change shape and size in response to incoming energy and particles from the sun. In extreme cases of space weather, nearby satellites can be engulfed by the belts, potentially charging the spacecraft or even short-circuiting internal electronics.
Scientists have predicted that the acceleration process discovered might be present, but this is the first time they have been able to see it with the right resolution. The Van Allen Probes showed the acceleration mechanisms acts much faster than standard models of Ultra-low-frequency (ULF) wave interactions, which is information scientists could use to adjust their understanding of belt dynamics.
This study can help scientists fine tune models of the belts until they become as accurate as possible. Mann said he will incorporate increased numbers of the ULF waves into his models and see how this matches up to observations of what is going on in the radiation belts.