Van Allen belts are among the main sources of radiation in space, causing electronic disturbances on board satellites and probes, and the degradation of solar panels.
Let’s continue our tour of the radiative environment. In the previous article, we talked about the solar wind and its interactions with the Earth’s magnetosphere. But what happens to charged particles that come into contact with the Earth’s magnetic field? We saw that some of them, carried by the solar wind, can fall from the tail of the magnetosphere to high latitudes and emit the light typical of auroras.
The particles that make up the van Allen belts. Credits: www.appuntidigitali.it
Other particles, typically energetic protons and electrons, are confined to low latitudes by the bottle effect. The motion of a particle that comes into contact with the Earth’s magnetic field is a spiral that wraps around the field lines. Proceeding from the equator to the poles, the particle perceives the growth of the magnetic field over time. Thus, according to Maxwell’s equations, it feels an electric field that changes its energy: the particle slows down. The particle slows down. This force can reverse the motion of the particles, which are forced to move back and forth along the field lines in what are called radiation belts.
iscovery of the Van Allen bands
These are called Van Allen belts, named after the American who led the work on the Explorer I satellite. When this was put into orbit in 1958, it began to record very high levels of radiation. Van Allen and his team attributed these to the presence of energetic particles confined by the magnetosphere. Subsequent missions (Explorer III, Pioneer III and Pioneer IV) helped describe the composition of the two radiation belts, one inner and one outer. The first, located at about 1.5-2 Earth radii, consists mainly of protons with energies above 30 MeV. The second, at about 5 Earth radii, is mainly due to the interaction of the magnetosphere with the solar wind, and is characterised by particles reaching an energy of a few MeV, up to a maximum of 10 MeV.
The different orbits in relation to the Van Allen belts. Credits: www.visionealchemica.com
Van Allen belts are perhaps the most important magnetospheric event: the design and operational life of probes and satellites largely depend on their interaction with energetic particles, which at the same time represent a hazard for astronautical activity in space.