A
radiation belt is a layer of
energetic charged particles that is held in place around a magnetized planet, such as the Earth, by the planet's
magnetic field. The Earth has two such belts and sometimes others may be temporarily created. The discovery of the belts is credited to
James Van Allen and as a result the Earth's belts are known as the
Van Allen belts. The main belts extend from an altitude of about 1,000 to 60,000 kilometers above the surface in which region
radiation levels vary. Most of the particles that form the belts are thought to come from
solar wind and other particles by
cosmic rays. The belts are located in the inner region of the Earth's
magnetosphere. The belts contain energetic
electrons that form the outer belt and a combination of
protons and electrons that form the inner belt. Other nuclei, such as
alpha particles, are less prevalent. The belts endanger
satellites, which must protect their sensitive components with adequate shielding if they spend significant time in the radiation belts. In 2013,
NASA reported that the
Van Allen Probes had discovered a transient, third radiation belt, which was observed for four weeks until destroyed by a powerful, interplanetary
shock wave from the
Sun.