SAN FRANCISCO--Earth's magnetic field whips charged particles into frenzied orbits around the planet in a surprisingly erratic fashion, new research has shown. Rapid changes in these ribbons of radiation may threaten satellites during an upcoming peak in energetic discharges from the sun, physicists reported here yesterday at a meeting of the American Geophysical Union. Already, the sudden birth of a short-lived but intense radiation belt last May might have doomed a satellite that supplied pager service to 45 million Americans.
Physicist James Van Allen discovered two bagel-shaped zones of energetic electrons hundreds of kilometers above Earth 40 years ago. The electrons whiz through space at 95% of the speed of light, tracing the lines of Earth's magnetic field. Scientists had long assumed that the strength of the Van Allen belts waxed and waned slowly. However, satellites in NASA's International Solar and Terrestrial Physics program have short-circuited that notion.
This year NASA satellites have witnessed the radiation belts grow hundreds of times more intense within minutes on several occasions, says space physicist Geoffrey Reeves of Los Alamos National Laboratory in New Mexico. In May, a new and powerful blast of electrons suddenly appeared within the 10,000-kilometer-wide gap that normally separates the two Van Allen belts. This may have overloaded the electronics of the widely used Galaxy 4 pager satellite on 19 May, Reeves suspects, forcing other satellites to take up the slack. Most other satellites, however, weathered the storm unscathed for reasons the researchers don't yet grasp.
At other times, the entire belts nearly vanished. "They are very dynamic," Reeves says. "That came as a surprise." Nevertheless, scientists hope the NASA fleet will yield accurate forecasts of this shifty "space weather" to help satellite operators know when to shut down--and to protect spacewalking astronauts from radiation exposure as they assemble the giant space station.
Prediction will become even harder during the next 2 years, when the 11-year sunspot cycle peaks and excites the magnetic field much more erratically, says atmospheric physicist Daniel Baker of the University of Colorado, Boulder. The satellite-zapping event last May, he says, was "a harbinger of what will come at the next solar maximum."