Van Allen Radiation Belts, two zones encircling the earth in which there are relatively large numbers of high-energy (fast-moving) charged particles. The particles are mainly protons and electrons, which are trapped within the belts by the earth's magnetic field. The belts were discovered in 1958 by a group of United States scientists under the direction of Dr. James Van Allen. The discovery was based on information obtained from Explorer I, America's first artificial satellite.
The Van Allen radiation belts are centered along the earth's magnetic equator in a region of the upper atmosphere called the magnetosphere, or exosphere. The innerand more intensebelt extends from roughly 600 miles (1,000 km) to 3,700 miles (6,000 km) above the earth; the outer belt, from roughly 9,300 miles (15,000 km) to 15,500 miles (25,000 km) above the earth. Scientists believe most of the particles that form the belts come from the solar wind, a continuous flow of particles emitted by the sun in all directions. Other particles probably have their origin in cosmic rays. In the late 1950's and early 1960's, artificial radiation belts were formed from charged particles produced by the detonation of nuclear explosives in space. These radiation belts, however, have weakened with time. The planets Jupiter and Saturn are encircled by radiation belts similar to the earth's Van Allen radiation belts.