Van Allen belt structure varies between one and three belts

Nature : Last year NASA launched a pair of spacecraft to study the structure of the Van Allen radiation belts. First detected 50 years ago, the belts were revealed by satellite data to consist of a pair of concentric donut-shaped rings of high-speed, highly charged particles, trapped and shaped by Earth’s magnetic field. Soon after NASA’s new probes were deployed, they detected a third ring forming between the two known rings at the same time that the outer ring was being eroded significantly. Over the next several months, the belts were observed to change structure several times, ranging from one to three stable rings. The variations and destruction of the outer and middle rings appear to be tied to shock waves caused by explosions of particles from the Sun. The current model of the structure of the Van Allen belts cannot explain the presence of the third ring. The new data show the significance of solar wind variations in relation to the belts’ behavior, but there is not yet enough information to form a new model.