Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Ultra-fast Electrons Explain Third Radiation Ring Around Earth

In the already complicated science of what creates – and causes constant change in – two giant doughnuts of radiation surrounding Earth, researchers have added a new piece of information: some of the electrons reach such enormous energies that they are driven by an entirely different set of physical processes. These results were published in a paper in Nature Physics on Sept. 22, 2013.

Understanding the nature of these radiation belts and how they swell and shrink over time is an integral part of interpreting, and perhaps someday predicting, the space weather that surrounds our planet. Such space weather can, among other things, cause complications in electronics systems aboard satellites we depend on for communications and GPS.

In September 2012, NASA's Van Allen Probes observed the radiation belts around Earth had settled into a new configuration, separating into three belts instead of two. Scientists think the unusual physics of ultra-fast electrons within the belt helped cause the unusual shape.
Image Credit: NASA/Goddard Space Flight Center

The discovery of the radiation belts was the first discovery of the space age, observed in 1958 by the Explorer I spacecraft. Scientists soon realized that the belts can change shape in concert with incoming disturbances from the sun, sometimes quite dramatically. In February 2013, researchers announced observations from NASA's Van Allen Probes, showing a previously undetected configuration. The belts showed a distinct unusually narrow ring beyond the inner belt persisting for a month in September 2012 while additional particles funneled in to create a third, larger, outermost belt. This previously unknown configuration of three bands, changed what was previously understood about the belts and set people in search of new explanations.

"The Van Allen Probes observations challenged our current views on the physics of the radiation belts," said Yuri Shprits, a space scientist at the University of California in Los Angeles and first author of the Nature Physics paper. "In the past we made estimates and thought they looked reasonable. Now we know we need to understand each storm in much more detail, creating global models that can reconstruct what's happening at every level."

So scientists began to work on new models to explain this new set of observations. The Van Allen Probes can measure the widest range of energies and particle types ever observed. Therefore, there were accurate measurements of particles in this narrow ring – moving up to 99.9 percent of the speed of light – which could shed light on physical processes never before seen.

"When I started in space sciences, we didn't even look at such energetic particles, as we were not sure that we could trust observations at these energies," said Dmitry Subottin, a co-author on the paper at UCLA. "The Van Allen Probes measurements give us confidence that these observations were reliable."

By comparing computer simulations of the belts with data from the Van Allen Probes, Shprits and his colleagues determined that one commonly understood method for how particles are accelerated to high energies did not work for these ultra-fast particles. The mechanism depends on one of the many unique and varied waves that can be present in an environment of charged particles, otherwise known as plasma, such as exists in the radiation belts. Waves known as Very Low Frequency Chorus waves move so that they can easily buffet particles in the belts up to higher speeds, much the way a perfectly timed push on a swing increases its speed. These same waves can be responsible for causing particles to precipitate down out of the belts into the atmosphere. These VLF Chorus waves affect fast electrons but not ultra-fast electrons. On the other hand, fast electrons in the belts are not affected by another wave called Electromagnetic Ion Cyclotron or EMIC waves, but this study showed just how strongly EMIC waves can affect the fastest moving particles. Indeed, the EMIC waves can help quickly deplete the most energetic particles, leaving behind only a narrow ring of radiation protected inside the boundary known as the plasmapause, as seen in the September 2012 event.

Another kind of VLF wave called Hiss is found inside this plasmapause boundary, and this wave does not strongly affect the ultra-fast particles that the Van Allen Probes observed residing in the persistent narrow ring. This explains why the narrow ring was stable for such a long time.

An earlier paper in Geophysical Review Letters, published July 28, 2013, provided similar explanations for the persistence of the third ring. The researchers in that paper, led by Richard Thorne who is a radiation belt scientist at UCLA, used data from both the Van Allen Probes and from NASA's THEMIS mission to model just how long it would take high energy particles to decay in the presence of a kind of VLF wave known as plasmaspheric hiss. The process might take only a few days for the slower particles, but took much longer for higher energy ones.

"The higher the energy, the longer the life time," said Thorne. "Our models show that if nothing happens to perturb the radiation belts, the highest energy electrons can stay for 100 days. In the September 2013 event, another storm came along and wiped that ring out after about a month, but before that the particles in the ring decayed as we predicted."

Thorne's model does not include EMIC waves in its explanation for why the particles in the outer ring depleted so quickly in that particular event. This goes to show how many questions are left about the wide variety of processes and waves that can affect different particles in the belts.

"The ultra-relativistic electrons of the third ring have so much energy that they are driven by very different physical processes," said Shprits. "Incorporating that information not only explains the unusual observation of the long-lived narrow middle ring, it opens up a new area of research for the ultra-relativistic particles."

Understanding which configurations and environments speed up these extremely fast particles helps with protecting spacecraft traveling through and near this region. Spacecraft can shield against particles – which can trip electronics systems inside satellites – up to a certain threshold speed, but such ultra-fast particles are able to travel through most shields. Knowing more about the radiation belts, and how different populations respond to the disturbances from the sun, can help satellite manufacturers protect future spacecraft from the effects of electrons within the Van Allen Belts.

For more information on the Van Allen Probes:
For more information on the Van Allen Probes' view of a third radiation belt:

Karen C. Fox
NASA's Goddard Space Flight Center, Greenbelt, Md.

Karen C. Fox | EurekAlert!
Further information:

More articles from Physics and Astronomy:

nachricht Significantly more productivity in USP lasers
06.12.2016 | Fraunhofer-Institut für Lasertechnik ILT

nachricht Shape matters when light meets atom
05.12.2016 | Centre for Quantum Technologies at the National University of Singapore

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

All Focus news of the innovation-report >>>



Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

Latest News

NTU scientists build new ultrasound device using 3-D printing technology

07.12.2016 | Health and Medicine

The balancing act: An enzyme that links endocytosis to membrane recycling

07.12.2016 | Life Sciences

How to turn white fat brown

07.12.2016 | Health and Medicine

More VideoLinks >>>