The belts are confined to a volume which extends about 65 ° on either side of the celestial equator. The Earth's atmosphere limits the belts' particles to regions above 200–1,000 km, (124–620 miles) while the belts do not extend past 8 Earth radii R E. The Sun does not support long-term radiation belts, as it lacks a stable, global dipole field. The term Van Allen belts refers specifically to the radiation belts surrounding Earth however, similar radiation belts have been discovered around other planets. The trapped radiation was first mapped by Explorer 4, Pioneer 3, and Luna 1. The second Soviet satellite Sputnik 2, followed by the US satellites Explorer 1 and Explorer 3, confirmed the existence of the belt in early 1958, later named after James Van Allen from the University of Iowa. Kristian Birkeland, Carl Størmer, Nicholas Christofilos, and Enrico Medi had investigated the possibility of trapped charged particles before the Space Age. Apollo Astronauts going through the Van Allen Belts received a very low and non-harmful dose of radiation. In 2013, the Van Allen Probes detected a transient, third radiation belt, which persisted for four weeks. The belts endanger satellites, which must have their sensitive components protected with adequate shielding if they spend significant time near that zone. Other nuclei, such as alpha particles, are less prevalent. The belts trap energetic electrons and protons. The belts are in the inner region of Earth's magnetic field. By trapping the solar wind, the magnetic field deflects those energetic particles and protects the atmosphere from destruction. Most of the particles that form the belts are thought to come from solar wind and other particles by cosmic rays. Earth's two main belts extend from an altitude of about 640 to 58,000 km (400 to 36,040 mi) above the surface, in which region radiation levels vary. The belts are named after James Van Allen, who is credited with their discovery. Earth has two such belts, and sometimes others may be temporarily created. A cross section of Van Allen radiation beltsĪ Van Allen radiation belt is a zone of energetic charged particles, most of which originate from the solar wind, that are captured by and held around a planet by that planet's magnetosphere.
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