Inside the magnetosphere, as in any dipole field, there are areas inaccessible to particles with kinetic energy E, less than critical. The same particles with energy E < E kr, who are already there, cannot leave these areas. These forbidden regions of the magnetosphere are called capture zones. In the capture zones of the Earth's dipole (quasi-dipole) field, significant fluxes of captured particles (primarily protons and electrons) are indeed retained.
To a first approximation, the radiation belt is a toroid, in which two regions are distinguished:
- an inner radiation belt at an altitude of ≈ 4000 km, consisting predominantly of protons with energies in the tens of MeV;
- outer radiation belt at an altitude of ≈ 17,000 km, consisting predominantly of electrons with energies in the tens of keV.
The height of the lower boundary of the radiation belt varies at the same geographical latitude in longitude due to the inclination of the axis of the Earth's magnetic field to the axis of rotation of the Earth, and at the same geographical longitude it changes in latitude due to the own shape of the radiation belt, due to different height of the Earth's magnetic field lines. For example, over the Atlantic, the increase in radiation intensity begins at an altitude of 500 km, and over Indonesia at an altitude of 1300 km. If the same graphs are plotted as a function of magnetic induction, then all measurements will fit on one curve, which once again confirms the magnetic nature of particle capture.
There is a gap between the inner and outer radiation belts, located in the range from 2 to 3 Earth radii. Particle fluxes in the outer belt are greater than in the inner one. The composition of the particles is also different: in the inner belt there are protons and electrons, in the outer belt there are electrons. The use of unshielded detectors has significantly expanded information about radiation belts. Electrons and protons with energies of several tens and hundreds of kiloelectronvolts, respectively, were discovered. These particles have a significantly different spatial distribution (compared to penetrating ones).
The maximum intensity of low-energy protons is located at a distance of about 3 Earth radii from its center (approximately at an altitude of 12,500 km from the surface). Low-energy electrons fill the entire capture region. For them there is no division into internal and external belts. It is unusual to classify particles with energies of tens of keV as cosmic rays, but radiation belts are a single phenomenon and should be studied in conjunction with particles of all energies.
The proton flux in the inner belt is quite stable over time. Early experiments showed that high energy electrons ( E> 1-5 MeV) are concentrated in the outer belt. Electrons with energies less than 1 MeV fill almost the entire magnetosphere. The inner belt is very stable, while the outer one experiences sharp fluctuations.
History of discovery
The existence of a radiation belt was first discovered by the American scientist James Van Allen in February 1958 when analyzing data from the American Explorer 1 satellite and was convincingly proven by recording periodically changing radiation levels during a full orbit of the Explorer satellite, specially modified by Van Allen to study the discovered phenomenon. 3". Van Allen's discovery was announced on May 1, 1958 and soon found independent confirmation in data from the Soviet Sputnik 3. A later re-analysis of data from the earlier Soviet Sputnik 2 showed that the radiation belts were also recorded by its equipment designed to analyze solar activity, but the strange readings of the solar sensor were then unable to be interpreted correctly. Soviet priority was also negatively affected by the lack of recording equipment on Sputnik (it was not provided on Sputnik 2, and it was broken on Sputnik 3), due to which the data obtained turned out to be fragmentary and did not provide a complete picture of changes in radiation with altitude and the presence in near-Earth space of not just cosmic radiation, but a characteristic “belt” covering only certain altitudes. However, the more diverse equipment of Sputnik 3 helped clarify the “composition” of the inner belt. At the end of 1958, analysis of data from Pioneer 3 and the slightly later Luna 1 led to the discovery of the existence of an outer radiation belt, and American high-altitude nuclear explosions demonstrated that humans can influence the Earth's radiation belts. The analysis of these data led to the gradual formation, since mid-1959, of modern ideas about the existence of two radiation belts around the Earth and the mechanisms of their formation.
History of research
On August 30, 2012, two identical RBSP probes were launched from the Cape Canaveral Space Center using an Atlas V 410 rocket into a highly elliptical orbit with an apogee altitude of about 30 thousand kilometers Radiation Belt Storm Probes), designed to study radiation belts. They were subsequently renamed "Van Allen Probes" ( Van Allen Probes). Two devices were needed in order to distinguish changes associated with the transition from one region to another with changes occurring in the belts themselves. . One of the main results of this mission was the discovery of a third radiation belt, which appears for a short period of time on the order of a few weeks. As of February 2017, the operation of both probes continued.
Radiation belts of planets
Due to the presence of a strong magnetic field, the giant planets (Jupiter, Saturn, Uranus and Neptune) also have strong radiation belts, reminiscent of the Earth's outer radiation belt. Soviet and American space probes have shown that Venus, Mars, Mercury and the Moon do not have radiation belts.
History of research
see alsoNotesLiterature
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A.M.GALPER
Moscow Engineering Physics Institute
1. Introduction
The region of the nearest near-Earth space in the form of a ring surrounding the Earth, in which huge flows of protons and electrons captured by the Earth's dipole magnetic field are concentrated, is called (RPZ). Abroad, it is usually called the Van Allen belt. RRP was discovered by American and Soviet scientists in 1957-1958. Since then, a huge number of experiments have been carried out in space, making it possible to study the basic properties and features of the ERP. Radiation belts similar to the Earth's exist on planets that have a magnetic field and an atmosphere. Thanks to American interplanetary spacecraft, they were discovered at, and.
What is RPP? Qualitatively, this can be explained as follows. The Earth's dipole magnetic field is a set of magnetic shells nested within each other. Its structure resembles an onion or a head of cabbage. A magnetic shell can be defined as a closed surface woven from magnetic lines of force. The closer the shell is to the center of the dipole, the greater the magnetic field strength and momentum required for a charged particle to penetrate from outside to this shell. Thus, N-th shell is characterized by the momentum of the particle P N. If the initial momentum of the particle is less than P N, then the magnetic field will reflect it and the particle will return to outer space. If this particle somehow ends up on N-th shell, then she will no longer be able to leave it. Such a trapped particle will remain trapped until it dissipates or loses energy upon impact with the residual atmosphere.
2. General description of the RPP
2.1. Earth's magnetic field
The Earth's magnetic field is a dipole, the axis of which makes an angle of 11° with the Earth's rotation axis, does not pass through the geometric center of the Earth's rotation, but is shifted 342 km in the direction opposite to the eastern tip of Brazil. The polarity of the Earth's magnetic field is opposite to the geographic one. The North Magnetic Pole is located in the south, in Antarctica, and the South Pole is in the north, in Canada. Thus, Moscow, located at 56° northern geographic latitude, has a southern magnetic latitude of 51°. Earth's magnetic moment M= 8.1 10 25 G cm 3, and the average magnetic field strength at the Earth's surface is ~ 0.4 G. There is still no generally accepted theory of the origin of the Earth's magnetic field. Among the available hypotheses, two are the most plausible: the field is caused by the rotating iron core of the Earth or a giant electric current encircling the Earth at a great distance from the center of the Earth.
The inclination and displacement of the dipole axis relative to the axis of rotation, as well as the magnitude of the magnetic moment, determine only the general picture of the Earth's magnetic field. At short distances from the Earth, the field is somewhat distorted under the influence of magnetic anomalies: Brazilian, South Atlantic, Northern, etc. At distances of more than 6-7 Earth radii, it is significantly distorted by the solar wind (magnetic field frozen into the solar wind plasma). In Fig. Figure 1 shows a picture of the space occupied by the Earth's magnetic field and called the magnetosphere. it is strongly flattened on the side of the Sun and very elongated on the opposite side (that is, at night). The “tail” of the Earth’s magnetosphere extends to the trajectory of the Moon. It is in the elongated part of the magnetosphere that breaks in magnetic field lines sometimes occur, and through them the solar wind breaks through into the magnetosphere.
At distances less than 6-7 Earth radii, the magnetic field can be considered almost dipole, spherically symmetrical and independent of longitude. Then the magnetic field strength at any point in space is determined as
In a flat two-dimensional approximation, each point can be defined by the magnetic field line on which it is located and the angle, that is, the magnetic latitude. In this case, the magnetic field line itself can be “marked” by the distance between the equatorial point of this line and the center of the dipole and expressed in relative units L = r eq/ r h, where r eq is the distance from the equatorial point to the center of the dipole, and r z is the radius of the Earth. Thus, a magnetic field line with the parameter L= 1 has an equatorial point on the Earth's surface.
The position of any point in the Earth's magnetosphere can be indicated either by three-dimensional geographic coordinates or by a magnetic coordinate system. Typically, a magnetic coordinate system ( L, B), called the McIlwain coordinate system after the scientist who proposed it.
2.2. Movement of particles in the Earth's magnetic field
1. If in a magnetic field the velocity of a charged particle is directed at a certain angle q (the so-called pitch angle) to the direction of the magnetic field line where the particle is located, then the velocity vector ee can be decomposed into two components: tangent to the magnetic field line and perpendicular to her. The motion of such a particle can be represented as Larmor rotation around a magnetic field line (the center of rotation of a particle in a magnetic field is called the leading center) and translational (movement of the center of rotation along a magnetic field line). As a result of the addition of these components, the particle moves along a spiral trajectory, winding around magnetic field lines, and if these magnetic lines are closed, the usual effect of magnetic confinement occurs (Fig. 2).
Radius of rotation R l around the field line, usually called the Larmor force, is determined from the equality of the centrifugal force and the Lorentz force. Circulation period T l is
| (2) |
Where m- particle mass, c- speed of light, Ze is the charge of the particle, and is the velocity component perpendicular to the magnetic field.
We assume that the magnetic field is sufficiently uniform and stable: its changes in space and time are very small over the Larmor radius and one revolution period, which is why the conditions are met
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(3) |
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(4) |
2.3. Spatial and energy distributions of trapped particles in the Earth's radiation belt
In the Earth's magnetic field, the same shell at different longitudes is at different distances from the Earth's surface due to the mismatch of the rotation axis with the axis of the magnetic field. This effect is most noticeable above the Brazilian Magnetic Anomaly, where magnetic field lines descend and trapped particles moving along them risk ending up below an altitude of 100 km and dying in the Earth's atmosphere.
The distribution of electrons and protons within the belt is unequal. In particular, from Fig. 4 it can be seen that protons are located in the inner part of the belt, and electrons are located in the outer part. Therefore, at the discovery and at the early stage of research of the radiation belt, it was believed that there were two belts: the inner one - proton and the outer one - electron.
2.4. The nature of radiation belt particles
The most significant mechanism for the generation of particles filling the ERB is the decay of albedo neutrons. Neutrons are produced by the interaction of cosmic radiation with the atmosphere. The neutron flux away from the Earth (albedo neutrons) passes unhindered through its magnetic field. However, they are unstable and decay into protons, electrons and electron antineutrinos. Depending on the magnetic field strength at the point of neutron decay and the pitch angles of electrons and protons, they will be captured or leave the ERB. Albedo neutrons supply the radiation belt with protons with energies up to 10 3 MeV and electrons with energies up to several MeV.
The second mechanism is radial diffusion. The solar wind plasma, flowing around the magnetosphere, bursts into the Earth’s magnetic field from the side of the magnetosphere’s tail, and charged particles, once on the magnetic field line, are captured and participate in all three movements described above. Being on a certain ley line L, the captured particle has the corresponding energy E, and EL 3 = const. Indeed, it follows from the expression that ~ ( E/B) ~ const. Considering that B ~ r -3 ~ L-3 , we get EL 3 = const. With a sharp change in solar wind pressure, the magnetic field can change greatly even during one revolution of the particle around the globe. Then the second condition of adiabaticity is violated and the particle moves to a shell with a smaller L. There is an increase in energy due to a change in the magnetic field. This is a relatively slow acceleration process, but it additionally supplies the radiation belt with protons and electrons up to an energy of ~30 MeV. The outer part of the ERB is mainly formed by this mechanism, and since this source depends on magnetic disturbances, the outer electron belt is quite dynamic and changeable, unlike the inner part.
There are several other mechanisms for pumping the belt with high-energy particles. For example, albedo atmospheric electrons and protons, resulting from the interaction of primary protons with nuclei in the upper atmosphere, are scattered in the residual atmosphere and captured in the ERB, or high-energy radioactive albedo nuclei undergo decay within the capture zone and replenish the radiation belt with electrons and positrons.
During strong magnetic storms, particles not only accelerate, but also spill out of the belt. The fact is that changes in the configuration of the magnetic field can plunge mirror points into the atmosphere and particles, losing energy (scattering, ionization losses), change pitch angles and die in the upper layers of the magnetosphere.
The ERP is surrounded by a so-called plasma layer (trapped flows of electrons and protons (ions) with a density of ~1 cm -3 and an energy of up to 1 keV) (Fig. 1). One of the reasons for the occurrence of northern (aurora) lights is the precipitation of particles from the plasma layer and partly from the external ERB. The phenomenon of “northern lights” is the radiation of atmospheric atoms excited as a result of collisions with particles falling out of the belt.
3. Results of the study of the Earth’s radiation belt
Almost all the results of research into the ERP, which made it possible to create a fundamental physical picture of this phenomenon, were obtained in the 1960-1970s. The latest research using interplanetary spacecraft, orbital stations and new generation scientific equipment has provided very important new data on the EPR.
3.1. Detection of a stationary belt of high energy electrons
In the early 80s, MEPhI scientists studied the flows of high-energy electrons in the immediate vicinity of the Earth using equipment installed at the Salyut-6 orbital station. The equipment made it possible to isolate flows of electrons and positrons with an energy of more than 40 MeV with high efficiency. The orbit of the Salyut-6 station (altitude 350-400 km, inclination 52°) mainly passed below the Earth’s radiation belt, but in the region of the Brazilian magnetic anomaly it touched the inner part of the RZ. And precisely, when the station crossed the Brazilian anomaly, stationary flows of high-energy electrons were discovered (Fig. 3). Before this experiment, only electrons with an energy of no more than 5 MeV were recorded in the ERP (in accordance with the albedo mechanism of origin).
The MEPhI group carried out subsequent measurements on artificial Earth satellites of the Meteor-3 series (altitude of circular orbits 800 and 1200 km). The device penetrated deeply into the radiation belt and confirmed the results obtained at the Salyut-6 station - the existence of a stable belt of high-energy electrons. Then the MEPhI group obtained an even more important result using magnetic spectrometers installed at the Salyut-7 and Mir stations. It has been proven that the stable belt consists only of electrons (without positrons) of high energy (up to 200 MeV). This means that a very effective acceleration mechanism is realized in the Earth’s magnetosphere (the observed acceleration cannot be explained by radial diffusion alone). Currently, measurements at the Mir station continue.
3.2. Detection of a stationary belt of CNO nuclei
In the late 80s - early 90s, a group of scientists from the NINP MSU set up an experiment to study nuclei located in nearby outer space. The measurements were carried out on satellites of the Cosmos series using nuclear photoemulsions and proportional cameras. Fluxes of O, N and Ne nuclei were discovered in the region of outer space where the orbit of an artificial satellite ( H~ 400-500 km, inclination 52°) crossed the Brazilian anomaly. The analysis showed that these nuclei with energies up to several tens of MeV/nucleon could not be albedo, galactic, or solar in origin, since with such energy they could not penetrate so deeply into the Earth’s magnetosphere. This is the so-called anomalous component of cosmic rays captured by the magnetic field (Fig. 3). Low-energy atoms of interstellar matter penetrate into the heliosphere. Ultraviolet radiation from the Sun can once - and less often twice - ionize atoms. The resulting charged particles are accelerated at shock fronts to several tens of MeV/nucleon and penetrate deep into the magnetosphere, where they are completely ionized and captured.
3.3. Quasi-stationary belt of electrons and protons
On March 22, 1991, a powerful flare occurred on the Sun, accompanied by the ejection of a large mass of solar matter. By March 24, the substance reached the magnetosphere and transformed its outer region. Energetic solar wind particles burst into the magnetosphere and reached the shell L~ 2.6, on which the American CRESS satellite was located at that time (orbital altitude at apogee ~ 33.6 thousand km, at perigee 323 km, inclination 18°). Instruments installed on this satellite recorded a sharp increase in the fluxes of electrons with an energy of ~15 MeV and protons with an energy of 20-110 MeV, indicating the formation of a new belt on L= 2.6 (Fig. 3). The quasi-stationary belt was first observed on various spacecraft, but only on the Mir station for almost the entire two-year lifespan. Using the MEPhI magnetic spectrometer, the charge composition of the quasi-stationary belt was determined and the energy spectrum of the particles was measured.
In connection with the formation of a quasi-stationary belt of solar origin, let us recall that in the 60s, as a result of explosions of nuclear devices in space, a quasi-stationary belt of low-energy electrons was formed, which existed for about 10 years. The source of the charged particles was the decay of radioactive fission fragments.
3.4. Seismomagnetic connections
A detailed study of changes in the fluxes of high-energy captured particles, carried out by MEPhI at the Salyut-6, Mir orbital stations and the Meteor satellite, led to the discovery of a new natural phenomenon associated with the impact of the Earth's seismic activity on the internal boundary - seismomagnetosphere coupling. The physical explanation of this phenomenon comes down to the following. Electromagnetic radiation is emitted from the epicenter of the upcoming earthquake, resulting from mechanical movements of underground rocks (friction, cracking, piezoelectric effect, etc.). The frequency spectrum of the radiation is quite wide. However, only radiation in the frequency range ~ 0.1-10 Hz can achieve ERP, passing through the earth's crust and atmosphere practically without losses. Having reached the lower limit of the EPR, electromagnetic radiation interacts with trapped electrons and protons. Actively participating in the interaction are particles attached to those magnetic lines of force (more precisely, to tubes of lines) that pass through the epicenter of the upcoming earthquake. If the frequency of particle oscillations between mirror points coincides with the frequency of seismic electromagnetic radiation (SEMR), the interaction will acquire a quasi-resonance character, manifested in a change in the pitch angles of captured particles. If at the mirror point the pitch angle of the particle becomes different from 90°, this will inevitably cause a decrease in the mirror point, accompanied by the precipitation of particles from the radiation belt (Fig. 5). Due to the longitudinal drift of captured particles, the precipitation wave (that is, the particles moving downward) circles the Earth, and a precipitation ring is formed along the magnetic latitude at which the epicenter of the upcoming earthquake is located. The ring can exist for 15-20 minutes until all particles die in the atmosphere. A spacecraft in orbit passing under the radiation belt will register a burst of precipitating particles when it crosses the latitude of the epicenter of the upcoming earthquake. Analysis of the energy and time distributions of particles in the recorded bursts makes it possible to determine the location and time of the predicted earthquake (Fig. 5). The discovery of a connection between seismic processes and the behavior of trapped particles in the Earth's magnetosphere formed the basis of a new method of operational earthquake forecasting that is currently being developed.
4. Conclusion
Recently, significant efforts have been aimed at refining mathematical models of the EPR, which make it possible to predict particle fluxes and radiation doses taking into account solar activity. But at the same time, direct experimental and theoretical studies of RPR continue, which are of great scientific and practical interest.
The beginning of astronautics was marked by a number of discoveries, one of which was the discovery of the Earth's radiation belts. The Earth's inner radiation belt was discovered by American scientist James van Allen after the Explorer 1 flight. The Earth's outer radiation belt was discovered by Soviet scientists S. N. Vernov and A. E. Chudakov after the Sputnik-3 flight in 1958.
At some altitudes, the first satellites fell into areas that were densely saturated with charged particles with very high energy, sharply different from previously observed cosmic particles, both primary and secondary. After processing data from satellites, it became clear that we are talking about charged particles captured by the Earth's magnetic field.
It is known that any charged particles, once in a magnetic field, begin to “wrap” around the magnetic field lines, simultaneously moving along them. The dimensions of the turns of the resulting spiral depend on the initial speed of the particles, their mass, charge and the strength of the Earth's magnetic field in the region of near-Earth space into which they flew and changed the direction of movement.
The Earth's magnetic field is not uniform. At the poles it “condenses” - becomes denser. Therefore, a charged particle that has begun to move in a spiral along the magnetic line “ridden” by it from a region close to the equator, as it approaches any pole, experiences more and more resistance until it stops. And then it returns back to the equator and further to the opposite pole, from where it begins to move in the opposite direction. The particle finds itself, as it were, in a giant “magnetic trap” of the planet.
These regions of the magnetosphere, where high-energy charged particles (mainly protons and electrons) and particles with kinetic energy E less than critical accumulate and are retained, are called radiation belts. The Earth has three radiation belts, and now a fourth has been discovered. The Earth's radiation belt is a toroid.
The first such belt begins at an altitude of approximately 500 km above the western and 1500 km above the eastern hemisphere of the Earth. The largest concentration of particles in this belt - its core - is located at an altitude of two to three thousand kilometers. The upper limit of this belt reaches three to four thousand kilometers above the Earth's surface.
The second belt extends from 10-11 to 40-60 thousand km with a maximum particle density at an altitude of 20 thousand km.
The outer belt begins at an altitude of 60-75 thousand km.
The given boundaries of the belts are still only approximately determined and, apparently, change periodically within some limits.
These belts differ from each other in that the first of them, closest to the Earth, consists of positively charged protons with very high energy - about 100 Moe. Only the densest part of the Earth's magnetic field could capture and hold them. The flow of protons in it is quite stable over time and does not experience sharp fluctuations.
The second belt consists mainly of electrons with energies of “only” 30-100 keV. Larger flows of particles move in it than in the inner belt, and it experiences sharp fluctuations.
In the third belt, where the Earth's magnetic field is weakest, particles with an energy of 200 eV or more are retained.
In addition, electrons with energies less than 1 MeV fill almost the entire capture region. There is no division into belts for them; they are present in all three belts.
To understand how dangerous charged particles in radiation belts are for all life on Earth, let’s give an example for comparison. Thus, ordinary X-ray radiation, used briefly for medical purposes, has an energy of 30-50 keV, and powerful installations for x-raying huge ingots and blocks of metal - from 200 keV to 2 MeV. Therefore, the most dangerous for future cosmonauts and for all living things when flying to other planets are the first and second belts.
That is why scientists are now trying so hard and carefully to clarify the location and shape of these belts, and the distribution of particles in them. So far only one thing is clear. The corridors for habitable spacecraft to enter routes to other worlds will be areas close to the Earth's magnetic poles, free from high-energy particles.
The natural question is: where did all these particles come from? They are mainly thrown out from its depths by our Sun. It has now been established that the Earth, despite its enormous distance from the Sun, is located in the outermost part of its atmosphere. This, in particular, is confirmed by the fact that every time solar activity increases, and therefore the number and energy of particles emitted by the Sun increase, the number of electrons in the second radiation belt increases, which, as if under the pressure of the “wind” of these particles, is pressed towards Earth.
The separation of charges into layers and the formation of the Earth's radiation belts occurs under the influence of the acousto-magnetoelectric effect, which consists in the fact that short-wave radiation from the Sun, passing through the plasma across the lines of force of the Earth's magnetic field, sorts the charges according to their energy state into different levels. The presence of a certain number of charges in each layer, including on the surface of the Earth, gives reason to assume that the Earth, together with the entire atmosphere, can be considered as an electrical machine, which in design can be identified with a spherical multilayer, multi-rotor, asynchronous electrical capacitive-inductive machine.
Particles captured in the Earth's magnetic trap under the influence of the Lorentz force undergo oscillatory motion along a spiral trajectory along the magnetic field line from the Northern Hemisphere to the Southern Hemisphere and back. At the same time, the particles move more slowly (longitudinal drift) around the Earth.
When a particle moves in a spiral in the direction of increasing magnetic field (approaching the Earth), the radius of the spiral and its pitch decrease. The particle velocity vector, remaining unchanged in magnitude, approaches a plane perpendicular to the direction of the field. Finally, at a certain point (called a mirror point) the particle is “reflected”. It begins to move in the opposite direction - to the conjugate mirror point in the other hemisphere.
A proton with an energy of ~ 100 MeV completes one oscillation along the field line from the Northern Hemisphere to the Southern Hemisphere in a time of ~ 0.3 sec. The residence time (“life”) of such a proton in a geomagnetic trap can reach 100 years (~ 3×109 sec), during which time it can make up to 1010 oscillations. On average, captured high-energy particles make up to several hundred million oscillations from one hemisphere to the other.
Longitudinal drift occurs at a much lower speed. Depending on the energy, the particles make a full revolution around the Earth in a time from several minutes to a day. Positive ions drift westward, and electrons drift eastward. The motion of a particle in a spiral around a magnetic field line can be represented as consisting of a rotation about the so-called. instantaneous center of rotation and translational movement of this center along the line of force.
The first American space satellite, Explorer 1, launched in 1958, soon confirmed the scientific value of space exploration. Thanks to an onboard experiment, a belt of radiation was discovered 1000 km above the Earth's surface, 100 million times higher than the natural background radiation of the planet. A second such radiation zone was discovered later at an altitude of 20,000 km.
These regions of the zone are known as the “Van Allen belts” (named after the physicist James Van Allen, whose experiment helped identify them). They consist of charged particles from cosmic rays and solar wind, attracted by the Earth's magnetic field. Each of the belts forms a torus (a donut-shaped figure) around the Earth. The ratio and energy level of charged particles differ in the inner and outer belts.
As shown in the top diagram, the Van Allen belts are filled with highly charged protons. The bottom diagram illustrates the content of highly charged electrons (areas of highest concentration are highlighted in dark color).
Inner Van Allen Belt
Most of the protons and electrons in the inner Van Allen belt are products of neutron decay. The latter, in turn, are the result of collisions of cosmic ray particles with hydrogen and helium atoms in the upper layers of the atmosphere
Van Allen outer belt
The inner and outer belts differ in their composition and charge strength. The outer one picks up particles primarily from the solar wind rather than cosmic rays. There are more protons in the inner Van Allen belt than in the outer one.
Belt structure
There is no clear boundary between the two Van Allen belts - the inner belt gradually turns into the outer one. These two radioactive zones, as already noted, differ in the composition of their particles and the degree of their charge.
Earth's magnetic field
The Earth is like a huge magnet, whose lines of force form the magnetosphere. The pressure of the solar wind plasma compresses the magnetosphere on the day side of the planet and stretches it on the night side. The protons and electrons that make up the plasma are captured by the magnetic field due to their electrical charge. The Van Allen belts extend from approximately 1,000 to 25,000 km from Earth.
Until now, it was believed that the radiation in the inner Van Allen belt was quite strong. And here the established opinion has recently been destroyed by research that has shown that in fact the most energetic electrons, the fastest, which are in the inner belt, are quite rare. So the astronauts can exhale. They are now not so afraid to fly in that area, since there is no danger of severe health damage from radiation.
The latest data should help scientists understand, as well as document, the effects of high-lying nuclear explosions. Moreover, the work is carried out in difficult conditions, when it is necessary to detect weak signals through a strong background of interference. The researchers compare their work to searching for a pair of snowflakes in a heavy rainstorm. After all, this downpour must somehow be ignored in order to study the snowflakes in more detail, to understand what they are, how they are formed, and so on.
What is a Van Allen Belt?
Essentially, the Van Allen Belt is two ring-shaped zones consisting of charged particles. And all this surrounds our planet. Unfortunately, past missions have failed to distinguish between electrons and high-energy protons in the inner belt. But today a special device is used, the Magnetic Electron and Ion Spectrometer - MagEIS, which made it possible to examine individual particles of the belt using probes. Unusual facts were discovered. In the inner belt there is not a single superfast electron, known as relativistic.
Of course, all laboratories in the world are showing great interest in space weather forecasts for our devices: satellites, ships. It is not for nothing that there is a special agreement banning nuclear weapons tests in space.
So far, Van Allen observations have shown that the outer belt is much more active, and when magnetic storms intensify and solar wind particles hit our system, it begins to pulsate. The belt seems to grow and immediately shrinks in response to such a stimulus. The inner belt is more stable. Unless the storm is too intense, it can push relativistic electrons deeper and closer to the Earth.