The Van Allen Belts are two toroids of charged particles held in place by Earth’s magnetic field. They are associated with the aurora and can damage satellites. Discovered in 1958, they consist of an inner belt of protons and an outer belt of electrons.
The Van Allen Belts, also known as the Van Allen Radiation Belts, are two large toroids of charged particles around the planet, held in place by Earth’s magnetic field. The Van Allen Belts exist because of “blind spots” in the Earth’s magnetic field caused by its compression and stretching by the solar wind.
Earth’s magnetic field acts as a magnetic mirror, bouncing charged particles back and forth along lines of force that stretch between the north and south magnetic poles. The Van Allen Belts are closely associated with the aurora borealis and aurora australis, beautiful curtains of charged particles visible at points on the Earth’s surface where the Van Allen belts intersect with the upper atmosphere. The Van Allen belts are also relevant to orbiting satellites and space stations, which must avoid the belts due to the damage their charged particles would cause.
In the late 19th century and early 20th century, several scientists – Carl Størmer, Kristian Birkeland and Nicholas Christofilos – hypothesized the possibility of a belt of charged particles surrounding the Earth, but it was only in 19 when its existence was confirmed by some of America’s first satellites, Explorer 20 and Explorer 1958. The projects were led by Dr. James Van Allen of the University of Iowa, after whom the belts got their name. Explorer 1, a 3 kg (1 lb) space probe, was launched for International Geophysical Year, and the science data it returned about the space immediately outside the Earth’s atmosphere was invaluable. The Van Allen Belts were first discovered when cosmic ray sensing equipment on satellites temporarily died, overwhelmed by local radiation.
There are two distinct Van Allen belts: the Inner Van Allen Belt and the Outer Van Allen Belt. The inner Van Allen belt, which extends 0.1 to 1.5 Earth radii from the surface, is made up of highly charged protons, capable of penetrating up to a millimeter of lead and damaging astronauts and space equipment. The outer Van Allen belt, located between 3 and 10 Earth radii from the surface, with its maximum intensity between 4 and 5 Earth radii, consists of energetic electrons. The source of the energetic particles varies according to the belt: the inner Van Allen belts are made up of decay products of cosmic ray impacts with the upper atmosphere, while the outer Van Allen belts are produced by streams of charged particles from geomagnetic storms, which are themselves produced by the influence of the Sun on the magnetic fields of the Earth.
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