Location of the Radiation BeltsThere is a large outer belt that follows the magnetic field lines essentially from the north to south poles around the planet. This belt begins around 8,400 to 36,000 miles above the the surface of the Earth. The inner belt does not extend as far north and south. It runs, on average, from 60 miles about the Earth's surface to about 6,000 miles. The two belts expand and shrink. Sometimes the outer belt nearly disappears. Sometimes it swells so much that the two belts appear to merge to form one big radiation belt.
What Is in the Radiation Belts?The composition of the radiation belts differs between the belts and also is affected by solar radiation. Both belts are filled with plasma or charged particles.
The inner belt has a relatively stable composition. It contains mostly protons with a lesser amount of electrons and some charged atomic nuclei.
The outer radiation belt varies in size and shape. It consists almost entirely of accelerated electrons. The Earth's ionosphere swaps particles with this belt. It also obtains particles from the solar wind.
What Causes The Radiation Belts?The radiation belts are a result of the Earth's magnetic field. Any body with a sufficiently strong magnetic field can form radiation belts. The Sun has them. So do Jupiter and the Crab Nebula. The magnetic field traps particles, accelerating them and forming belts of radiation.
Why Study the Van Allen Radiation Belts?The most practical reason to study the radiation belts is because understanding them can help protect people and spacecraft from geomagnetic storms. Studying the radiation belts will allow scientists to predict how solar storms will affect the planet and will allow advance warning in case electronics need to be shut down to protect them from radiation. This will also help engineers design satellites and other space craft with the right amount of radiation shielding for their location.
From a research perspective, studying the Van Allen radiation belts provides the most convenient opportunity for scientists to study plasma. This is the material that makes up around 99% of the universe, yet the physical processes occurring in plasma are not well-understood.