In 1958, the American scientist John Van Allen (1914– ) discovered two belts of radiation encircling Earth, now known as Van Allen belts. The belts are shaped like concentric doughnuts, with the doughnut hole over the North and South Poles of the planet. Van Allen, who had earned a doctorate in physics in 1939 from the University of Iowa, served as a naval officer during World War II and assisted in the development of the proximity fuse for naval artillery ordnance. He worked with captured V-2 rockets in upper-atmosphere tests and in developing research rockets for further exploration.
The inner belt, discovered first on the basis of data received from Geiger counters [V] carried aboard the early spacecraft Explorer 1 and Explorer 3, is within about 1 radius (4,000 miles) of the surface of the Earth. In December 1958 Van Allen’s group of researchers detected the second belt 9,000 to 12,000 miles beyond Earth. The radiation belts required that electronic equipment aboard spacecraft be shielded from their effects.
The charged particles in the belts derive from a variety of sources, including cosmic ray particles that collide with atmospheric atoms, and protons from magnetic storms. The inner belt largely consists of protons, and the outer belt, of protons with lower charges and electrons. At first it was assumed that the Van Allen belts accounted for the effect of the aurora borealis, but later research has suggested that the belts do not produce effects in the visual range and that the aurora derives from
Sun-emitted plasma or charged particles of the solar wind that have avoided capture by the belts and have been trapped closer to Earth, in its magnetic field. Later studies of the belts with satellites showed that their shape is less regular than originally assumed, being deformed by the effect of the solar wind.