Randy Otte, age 12, of Norwalk, Iowa, for his question:
What are the Van Allen radiation belts?
The Van Allen belts were introduced to the world as foes and quickly recognized as old friends. Way back in 1958, early satellites went aloft to explore the fringes of space. There they found regions of radiation that seemed to doom all hopes for space travel. Then we learned that the radiation belts actually protect the earth from radiation.
These enormous, lopsided doughnuts of radiation have enfolded the globe since earth's beginnings. But we were slow to recognize them. This part of the story began in the 1600s when Dr. Gilbert, who was Queen Elizabeth's private physician, became interested in magnets. He shaped a magnetic lodestone into a small globe and learned that the magnetic compass works because the earth itself is a giant magnet.
In the 1700s, Edmund Halley, who traced a famous comet, located the earth's magnetic poles.. In the 1800s, various scientists studied auroras to form a picture of the enormous magnetosphere that surrounds the earth. By the 1900s, it was known that the force lines of this stupendous magnetic field loop between the two magnetic poles, reaching high above the equator. A few researchers suspected that this huge magnetosphere might trap charged particles from the sun and perhaps from other outside sources. How right they were.
However, nobody was prepared for the truth when early satellites counted the charged particles and relayed back data from several hundred miles above the ground. The magnetosphere seemed to be a lethal blanket of dangerous radiation and future space travel seemed hopeless. Obviously, this was not so, though spacecraft must wear protective shields when they pass through the radiation belts that surround our planet.
They were named for James Van Allen, who did so much to launch the entire Space Age. The radiation in the two belts is caused by highly charged atomic particles, some of them oscillating at fantastic speeds. The inner belt contains mostly electrons and protons and their concentration is most intense about 2,000 miles above the earth, except in the polar regions. The outer belt contains mostly electrons and their densest concentration seems to be between 10,000 to 12,000 miles above the earth, except in the polar regions.
Since these electrically charged particles are trapped by the magnetosphere, its looping lines of magnetic force cause the belts to dip down to the magnetic poles.
No doubt many and perhaps most of the high energy particles are tossed out into space by solar flares and other dramatic events on the sun. Others may be caused by cosmic radiation from who knows where. When such particles strike a spaceship they create dangerous X rays and if this radiation reached the earth, it would be lethal to all forms of life. Fortunately, these electrical energies are trapped by the magnetosphere and the Van Allen belts form a planetary umbrella that protects us from outside radiation.