The Radiation Belts!

A Bit More History Because you can't see them from the ground, scientists didn't even know the Belts existed until the start of the Space Age in the late-1950's. When they put sensitive instruments inside satellites and launched them into space, they got a very big surprise. They found that the space around Earth was filled with fast-moving particles. Prof. James van Allen at the University of Iowa was very interested in particles called cosmic rays, which other physicists had detected from the ground as far back as the 1930's. What were cosmic rays? Where did they come from? No one seemed to know for sure. As soon as satellites could be built and orbited in space, van Allen and his team put instruments onboard satellites such as Explorer I and Pioneer 3, which could detect these fleeting particles before they entered the atmosphere. What they discovered when they looked at the data was far different than what they expected to find. As the satellite moved in its orbit, the instruments recorded a changing flow of cosmic ray particles along the orbit, but the changes were not random at all. By mapping out where the flow was strongest and weakest, they discovered over the course of many satellite studies, that there were clouds of very high energy particles near Earth. These clouds had a definite shape to them, being thickest in the equatorial plane, and thinning out as they approached either pole.  Careful satellite studies over the last 50 years show that there are actually two kinds of already familiar particles that make up the Belts: electrons and protons. The individual particles carry a lot of energy, and it is convenient to talk in terms of their energies in Volts when describing the Belt particles. This is where the story gets a bit interesting, because there are actually three different belts overlapping each other: There are two different kinds of electron belts and one kind of proton belt.

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