Trashing earth's radiation belts.

Trashing Earth's radiation belts

The clutter of huma debris circling the Earth -- inoperative satellites, spent rocket casings and many tinier bits -- has raised concern about its possible hazard to other orbiting objects, such as space stations and even the shuttle. But that is not its only effect. Andrei Konradi at NASA's Johnson Space Center in Houston notes that the growing amount of space trash may noticeably reduce the number of charged particles in Earth's Van Allen radiation belts.

What Konradi calls the "shell" of debris absorbs high-energy protons that spiral in toward the debris along the lines of Earth's magnetic field, so that "in the next decades we can expect a measurable decrease in [the protons'] fluxes," thus reducing the flow of charged particles in the radiation belts.

In 1986, the "debris environment" between Earth's surface and an altitude of about 1,500 miles had a total cross-sectional area roughly equal to three football fields, Konradi reports in the Dec. 2 SCIENCE. The increase in the area of the debris is difficult to predict, but Konradi assumes Soviet launch activity will stay at about its present level, while the lower amount of U.S. activity increases slightly for a time and then spurts. "By 2010," he writes, "it is expected to increase by about a factor of 8."

At present, he says, Earth's atmosphere is about 10 times as effective as the debris at shortening the length of time protons remain trapped in the radiation belts as they flash back and forth from pole to pole along the magnetic field lines. By 2010, however, at least as calculated between altitudes of about 300 and 1,000 miles and during the minimum in the sun's activity cycle, debris will be as good as or better than the atmosphere at shortening the particle lifetimes in the radiation belts, Konradi concludes.