It is generally understood that the Van Allen Radiation Belts are a result of the collision of Earth's magnetic field with the solar wind. Radiation from the solar wind then becomes trapped within the magnetosphere. The trapped particles are repelled from regions of stronger magnetic field, where field lines converge. This causes the particle to bounce back and forth between the earth's poles, where the magnetic field increases.
The presence of a radiation belt had been theorized prior to the Space Age and the belt's presence was confirmed by Explorer I on January 31, 1958 and substantiated by the Explorer III mission, under Doctor James Van Allen. The trapped radiation was first mapped out by Explorer IV and Pioneer III.
The Soviets once accused the United States of creating the inner belt as a result of nuclear testing in Nevada. Likewise, the United States has accused the USSR of creating the outer belt through nuclear testing. It is uncertain how particles from such testing could escape the atmosphere and reach the altitudes of the radiation belts. Likewise, it is unclear why, if this is the case, the belts have not weakened since atmospheric testing was banned by treaty.
The Van Allen radiation belt is a torus of energetic charged particles (ie. a plasma) around the Earth which are trapped by the Earth's magnetic field. When the Van Allen belts "overload", particles strike the upper atmosphere and fluoresce, causing the polar aurora. Qualitatively, it is very useful to view this belt as consisting of two belts around Earth, the inner radiation belt and the outer radiation belt. The particles are distributed such that the inner belt consists mostly of protons while the outer belt consists mostly of electrons.
It is generally understood that the Van Allen belts are a result of the collision of Earth's magnetic field with the solar wind. Radiation from the solar wind then becomes trapped within the magnetosphere. The trapped particles are repelled from regions of stronger magnetic field, where field lines converge. This causes the particle to bounce back and forth between the earth's poles, where the magnetic field increases.
The gap between the inner and outer Van Allen belts is caused by low-frequency radio waves that eject any particles that would otherwise accumulate there. Solar outbursts can pump particles into the gap but they drain again in a matter of days. The radio waves were originally thought to be generated by turbulence in the radiation belts, but recent work by James Green of the NASA Goddard Space Flight Center comparing maps of lightning activity collected by the Micro Lab 1 spacecraft with data on radio waves in the radiation-belt gap from the IMAGE spacecraft suggests that they're actually generated by lightning within Earth's atmosphere. The radio waves they generate only strike the ionosphere at the right angle to pass through it only at high latitudes, where the lower ends of the gap approach the upper atmosphere.
The term Van Allen Belts refers specifically to the radiation belts surrounding Earth; however, similar radiation belts have been discovered around other planets.
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