"The textbooks taught us for 50 years that there were two Van Allen belts: an outer belt that is highly dynamic and changing on relatively short time scales -- minutes, hours, maybe days -- and then the stable inner zone, separated by the slot region. So we fully expected to see that," physicist Daniel Baker, with the University of Colorado's Laboratory for Atmospheric and Space Physics, told Discovery News.
"When we turned on our instrument, we were in the middle of a very intense event -- a radiation belt enhancement extending to quite high energies in the outer belt. Just a couple days after that, the outermost part of that outer zone was torn away and we were left with this residual third ring. It just hung in there and hung in there and hung in there. It was so persistent that we thought there was something wrong with our instruments," Baker said.
The outer belt started to rebuild, leaving three belts and two slot regions -- a configuration remarkably different from what scientists had expected to see.
"It just stood out like a sore thumb," Baker said.
The third ring, sandwiched between the inner and outer belts, was first clearly detected on Sept. 2, 2012, and persisted until a shock wave blasted it and the entire outer belt away around Sept. 30.
The shock wave was triggered by a solar storm, called a coronal mass ejection, which releases about 1 billion tons of material out into the solar wind.
The discovery should help scientists improve forecasts for how the radiation belts change under particular circumstances, information that has a practical implication for the design and operation of satellites.
"Those kinds of radiation environments (around Earth) have not been taken into account in some of the modeling for (spacecraft) design and other purposes. That will have to be factored in," space weather researcher Louis Lanzerotti, with the Center for Solar-Terrestrial Research at New Jersey Institute of Technology, told Discovery News.
The inner Van Allen belt begins about 650 miles above Earth and extends to about 8,000 miles, although sometimes it dips as low as 125 miles -- well within the region where the International Space Station flies.
The outer belt begins at an altitude of about 8,000 miles and extends to about 26,000 miles, encompassing an area where communications and GPS satellites operate.
Particles in the belts come from the solar wind and get caught up in the tail part of Earth's magnetosphere. By some unknown process, some of those particles are accelerated, forming a seed population which gets trapped in outer fringes of Earth's magnetic field regions. Those particles then undergo another process that drives them deeper in the magnetosphere, resulting in particles that move at near light speed. The goal of the Van Allen Probes mission is to unravel these processes, which has implications far beyond understanding the space environment around Earth.
"Almost everything we can see with radio telescopes or optical or ultraviolet telescopes really is due to very energetic particles. So understanding how this cosmic acceleration process works is one of the holy grails of basic astrophysical research and here we have this wonderful laboratory in our own back yard," Baker said.
The research is published in this week's Science.