Paul Haig, age 15, of Providence, R.I., for his question:

WHAT CAUSES VAN ALLEN BELTS?

Van Allen radiation is a concentration of particles in two regions of space above the earth's atmosphere. These regions are called the "Van Allen belts."

The 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.

The Van Allen belts encircle the earth somewhat like irregularly shaped doughnuts. The inner belt is most dense about 2,000 miles above the earth. The outer belt is most dense from 10,000 to 12,000 miles up.

Astronomers don't agree on the source of the particles. The charged particles produce dangerous X rays when they strike spacecraft so special precautions must be taken to shield astronauts from this radiation.

The belts were named for James Van Allen, an American physicist who discovered the belts by using data from the United States Explorer and Pioneer satellites in 1958.