Subscribe free to our newsletters via your
. 24/7 Space News .




EARTH OBSERVATION
Ultra-fast Electrons Explain Third Radiation Ring Around Earth
by Karen C. Fox for Goddard Space Flight Center
Greenbelt MD (SPX) Sep 26, 2013


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. View a video on the phenomena here.

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.

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.

.


Related Links
Van Allen Probes
Earth Observation News - Suppiliers, Technology and Application






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle








EARTH OBSERVATION
Preparing to launch Swarm
Paris (ESA) Sep 23, 2013
With the launch of ESA's Swarm trio set for 14 November, the first satellite has arrived safely at the Plesetsk Cosmodrome in Russia. This new mission will unravel one of the most mysterious aspects of our planet: the magnetic field. The arrival marks the beginning of the 'launch campaign', which includes an intensive period of tests to make sure that the satellites are fit for launch afte ... read more


EARTH OBSERVATION
Mission to moon will boost research and awareness

Mighty Eagle Improves Autonomous Landing Software With Successful Flight

Watch Out for the Harvest Moon

Chang'e-3 lunar probe sent to launch site

EARTH OBSERVATION
NASA Rover Inspects Pebbly Rocks at Martian Waypoint

Martian Life: Good or Bad?

Communications Tests Go the Distance for MAVEN

Curiosity Rover Detects No Methane On Mars

EARTH OBSERVATION
"GRAVITY" is Almost Here

International Partnership Releases Space Exploration Benefits Paper

Iran to send second monkey into space

Voyager's departure from the heliosphere

EARTH OBSERVATION
Chinese VP stresses peaceful use of space

China's space station to open for foreign peers

Last Days for Tiangong

China civilian technology satellites put into use

EARTH OBSERVATION
New space crew joins ISS on Olympic torch mission

Station Crew Readies for Cygnus' Sunday Arrival

American, two Russians take shortcut to space

Tech glitch delays space station berthing to Saturday

EARTH OBSERVATION
Arianespace and Astrium sign deal to begin production of 18 new Ariane 5 vehicles

Problems with Proton booster fixed

Decontamination continues at Baikonur after Proton abortive launc

Russia launches three communication satellites

EARTH OBSERVATION
ESA selects SSTL to design Exoplanet satellite mission

Coldest Brown Dwarfs Blur Lines between Stars and Planets

NASA-funded Program Helps Amateur Astronomers Detect Alien Worlds

Observations strongly suggest distant super-Earth has water atmosphere

EARTH OBSERVATION
Green photon beams more agile than optical tweezers

Space oddity: the mystery of 2013 QW1

Domain walls as new information storage medium

Invention jet prints nanostructures with self-assembling material




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement