Bobby Sturgeon, age 8, of Youngstown, Ohio, for his question:
WHAT IS THE VAN ALLEN BELT?
The man who discovered the Van Allen radiation belts is a physicist named James Alfred Van Allen. Born in Mount Pleasant, Iowa, in 1914, Van Allen graduated from Iowa Wesleyan College and the University of Iowa. He was head of the University of Iowa's department of physics and astronomy and also one of the chief planners of the International Geophysical Year of 1957 1958.
Physicist James Alfred Van Allen discovered the radiation belts that circle the earth. Working with a team of scientists, Van Allen used data from the United States Explorer and Pioneer satellites to make his important discovery in 1958.
In two regions of space above the earth's atmosphere is a concentration of radiation. These regions, called the Van Allen belts, are part of a larger region of space, the magnetosphere, that surrounds the earth.
In the magnetosphere, the earth's magnetic field traps electrically charged particles and controls their behavior. The trapped particles reach particularly high concentrations in the two Van Allen belts.
Van Allen belts encircle the earth very much like irregularly shaped doughnuts. The inner belt is densest about 2,000 miles above the earth, while the outer belt is densest from 10,000 to 12,000 miles up.
The inner Van Allen belt seems to be made up mostly of protons and electrons, and the other belt is made almost entirely of electrons. when the belts were first discovered, astronomers believed these particles came from the thin stream of gases thrown off by the sun. These gases are called solar wind.
Later experiments seem to suggest other possible sources for the belts. Astronomers have still not been able to reach a general agreement on the source of the particles.
The charged particles in the Van Allen belts produce dangerous X rays when they strike a spacecraft. Because of this, special precautions must be taken to shield astronauts from the dangerous radiation.
Experiments conducted by physicist James Alfred Van Allen first detected the inner belt in 1958. When the Pioneer III space probe was made later that same year, Van Allen discovered the outer belt.