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Q. What is the Van Allen Belt? — Claude L.
A. It is a band of dangerous radiation high above Earth.
The Van Allen radiation belt is a region of protons and electrons surrounding Earth, held captive by our planet's magnetic field.

Actually, there are three or four such belts. The first belt we knew of was encountered by the first American space satellite, the 18-lb. Explorer 1 launched in 1958.

Van Allen. Explorer was built at the Jet Propulsion Laboratory, Pasadena, California. It carried cosmic ray Geiger counters built at the University of Iowa by physicist James Van Allen and graduate student Wei Ching Lin.

Van Allen's science package inside the tiny satellite discovered the previously-unknown radiation belt around our planet. The region was named the Van Allen Belt and was recognized as the greatest science contribution of the International Geophysical Year 1958.

More belts. There actually are three, and sometimes four, radiation belts surrounding Earth. Taken together, they often are referred to as the Van Allen radiation belts.
  • Innermost is the original Van Allen Belt at an altitude of about 4,000 miles above the equator. It contains very energetic protons, which are the result of collisions of incoming cosmic rays smashing into atoms of the atmosphere.

    An accumulation of such particles over many years can become very intense. In fact, the particles can become so intense they can punch right through a spacecraft. Long exposure can damage parts and instruments, and are a hazard to astronauts.

  • Pioneer 3 and Pioneer 4 were early spacecraft designed to fly toward Earth's Moon. They carried Geiger counters to measure radiation.

    When Pioneer 3 was launched in 1958, it discovered a second and outer radiation belt around Earth.

    Pioneer 4, launched in 1959, also detected the outer radiation belt.

    Scientists believe the outer radiation belt actually is plasma trapped in Earth's magnetosphere. The radiation belt label usually is applied to the more energetic part of the plasma.

  • In 1990, a spacecraft known as the Combined Release and Radiation Effects Satellite (CRRES) discovered a third radiation belt between the inner and outer belts.

  • In 1998, there were a series of huge disturbances on the Sun that caused a new radiation belt to form around Earth in the so-called slot region between the inner and outer belts. However, that new fourth belt disappeared once the solar activity subsided. With the Sun peaking in activity every eleven years, could the fourth belt return?
Treacherous. The radiation in the belts is concentrated closest to Earth at the poles where we see the aurora – Northern Lights and Southern Lights.

Satellites traveling near the radiation belts may be damaged severely, so spacecraft builders plan their orbits to spend as little time as possible in the radiation belts or even avoid the belts completely.

The level of radiation in the belts changes when magnetic storms on the Sun pelt Earth or nuclear explosions are set off on the surface of our planet.


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