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:
Karen C. Fox | EurekAlert!
Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences
Nano-kirigami: 'Paper-cut' provides model for 3D intelligent nanofabrication
16.07.2018 | Chinese Academy of Sciences Headquarters
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
16.07.2018 | Physics and Astronomy
16.07.2018 | Life Sciences
16.07.2018 | Earth Sciences