Tom Craviotte, age l3, of Eugene, Ore., for his question:
Where exactly are the Van Allen radiation belts?
Nowadays, people in the know never refer to empty space, for our probing satellites have proved that the vast reaches between the planets are populated with energetic particles. This knowledge unfolded bit by bit, arid the discovery of the Van Allen belts came as a great shock.
These amazing belts of radiation were discovered in l958 and there has not been time to survey them in exact detail. They are vast doughnut shaped areas of highly charged particles that exist between the earth and outer space. Early information on the two Van Allen belts is a vital study of our space program. Many satellites have gathered and relayed data, and We have learned ways for interplanetary spacecraft to escape the radiation hazards of the belts.
No one can pinpoint the exact boundaries of the hazardous areas. We can, however, give their approximate dimensions and shapes but they tend to change with solar activity. The outer boundary is figured in units of the earth's radius, which is about 4,000 miles. Above the equator on the day side of the globe it may extend eight and above the night side it may balloon up to l4 earth radii. A strong wind of particles from solar flares may push it even farther from earth.
The average scope of the outer belt extends up from 8,000 to 30,000 miles. The inner belt may extend from 300 to 3,400 miles. The amazing regions of radiation do not follow the pattern of our spherical globe. They exist because the earth is a mighty magnet and they follow its lines of magnetic force. As in a small bar magnet, these lines swoop out in wide loops and dip down to the two poles. Across section of a belt is like a crescent moon with the wide center above the magnetic equator and the two horn tapering down to touch near the earth's magnetic poles. A slice through both belts look like two crescent moons, outside the other.
A diagram showing the earth between cross sections of the belts shows just how spacecraft can avoid them. Above the earth's two magnetic pales there are cone shaped pockets free from radiation. At these points, interplanetary ships can take off without crossing through the hazardous belts. But when they were first discovered, no one knew this. The data from early satellites suggested that radiation might fill all of outer space. For a time it seemed that mankind must abandon his dream of visiting other worlds but later information proved this idea wrong.
The amazing radiation belts are named for James Van Allen whose dreams and plans led to the IGY that started the space Age. The first data on the radiation regions was transmitted from explorer I which was launched Jan. 3l, l958. The little satellite was 6 inches wide and 80 inches long. It carried probing equipment, and its total weight was 30.8 pounds. Its orbit of 224 to l,573 nautical miles above the earth plunged it into the fringes of the lower radiation. Later, other satellites charted the general pattern of the two Van Allen belts.