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What are the Van Allen radiation belts and how are particles trapped there?
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Ionosphere and magnetosphere
The layers of Earth's atmosphere, with a yellow line showing the air temperature at various heights.
The Van Allen radiation belts are two doughnut-shaped zones of highly energetic charged particles—primarily protons and electrons—trapped within Earth’s magnetic field. Centered on the Equator, these belts were discovered in 1958 by James A. Van Allen using data from early Explorer satellites.123
How Particles Are Trapped
Particles are trapped in these regions through the interaction between their motion and Earth's magnetic field lines:
- Spiral Motion: Charged particles travel in spiral paths along the magnetic field lines.123
- Magnetic Mirror Effect: As particles move toward the magnetic poles, the magnetic field strength increases. This causes the particles to be reflected back toward the opposite pole. Consequently, they bounce back and forth between the Northern and Southern hemispheres.123
- Origin: Particles in the inner belt largely originate from the decay of neutrons produced when cosmic rays strike the upper atmosphere. The outer belt contains particles from both the atmosphere and the solar wind.132
These trapped particles eventually collide with atoms in the thin atmosphere, which removes them from the belts over time.12