Earlier this year, NASA scientists discovered a “previously unknown surprise circling Earth” — an ephemeral third ring of radiation surrounding our planet. Now, some eight months later, UCLA scientists say they know what’s going on — and it’s unlike anything physicists have ever seen before.
Top image: The third ring between the two belts. The unusual ring, seen in red, persisted for four weeks following a plasma wave burst at the outer belt. (Credit: Yuri Shprits, Adam Kellerman, Dmitri Subbotin/UCLA)
As a quick recap, NASA scientists working with the Van Allen Probes reported the surprising discovery of a mysterious and narrow radiation ring that appeared briefly for about four weeks between the inner and outer rings in September 2012.
Now, radiation belts are nothing new to science — and in fact, the two doughnut-shaped Van Allen Belts were discovered as far back as 1958.
They’re comprised of energetic particles that are trapped by the Earth's geomagnetic field. The particles are primarily comprised of protons and electrons. Normally, the radiation belts form the characteristic two-zone structure known to most physics students: a stable inner zone and a highly variable outer zone. The outer zone is heavily influenced by very-low frequency plasma waves; it forms and disappears owing to various space conditions, namely wave-particle interactions that typically last about a day.
But this new third zone, which appears intermittently between the two known bands, behaves a bit differently.
Close to the Speed of Light
According to the new research, which was headed by UCLA’s Yuri Shprits, the third radiation zone exists at what the scientists are calling “ultrarelativistic energies,” while consisting of an additional medium narrow belt that lasts for about a month. This middle band is comprised of extremely energetic particles known as ultrarelativistic electrons — electrons so energetic that they move close to the speed of light. The region the belts occupy range from about 620 to 32,000 miles (1,000 to 50,000 km) above the Earth.
The team was able to draw this conclusion by pulling data from ground stations, which were then compared to the observations made by NASA’s Van Allen Probes. The researchers then performed simulations involving the physics of ultrarelativistic electrons and other space weather conditions with a model of Earth’s radiation belts for the period August to October 2012.
Different “Populations” of Particles
"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," noted Shprits in a release. Consequently, the Van Allen Belts can no longer be seen as one consistent mass of electrons. Rather, they behave according to their own energies and react to the various disturbances of space.
The key to the study was in distinguishing between the behavior of the super high-energy electrons and those at lower energies. The scientists observed that plasma waves produced by ions — which don't typically affect energetic electrons — propelled ultrarelativistic electrons from the outer ring nearly all the way down to the inner edge of the inner ring. Only a narrow ring of the super-high-energy electrons survived this space storm — a remnant the scientists observed as the third ring. And because a cold bubble of plasma formed around the Earth to protect the particles, the ring persisted for four weeks.
Disturbingly, ultrarelativistic electrons pose a severe danger to satellites and spacecraft. Because they pack so much motion (again, we’re talking about electrons that are moving at close to the speed of light), they pack a hell of a lof of energy — energy that could disrupt or even destroy critical satellites. It could even disrupt the proposed space elevator. Research like this could eventually lead to measures to protect both space equipment and astronauts.
Read the entire study at Nature: Physics: “Unusual stable trapping of the ultrarelativistic electrons in the Van Allen radiation belts.”