(ORDO NEWS) — Scientists have found that electrons in the Earth‘s radiation belts are accelerated to ultra-high energies in special zones. This is facilitated by the low plasma density. The observation results were published in the scientific journal Science Advances.
Radiation belts are called two areas of space, which are located at an altitude of 6 and 58 thousand kilometers from the Earth’s surface. High-energy electrons and protons accumulate inside them, which are “caught” by the planet’s magnetic field.
Under certain conditions, for example, during powerful flares on the Sun, these particles can enter the atmosphere, causing radio interference and auroras at high latitudes. Scientists have long been interested in how protons and electrons get into these belts and what physical processes accelerate them to ultrahigh energies.
To study the radiation belts, NASA launched two Van Allen Probes into orbit in 2012. Almost immediately after launch, the probes discovered a third radiation belt, which periodically arises between the other two. In addition, they discovered many oddities in the behavior of electrons in Earth’s orbit.
In particular, scientists have suggested the mechanism by which they accelerate – the so-called “chorus”. It represents special electromagnetic waves that circulate through the plasma of the radiation belts. However, his discovery did not explain in any way why the energy of some electrons reached 7 megaelectronvolts (MeV) – this is several times higher than the maximum value that the “chorus” could give them.
Previously, it was believed that high-energy electrons can penetrate the radiation belts from the outside or accelerate during magnetic substorms – a local type of planetary magnetic storms. Despite their best efforts, scientists have been unable to find evidence to support both hypotheses.
In a new study, scientists led by professor at the University of Potsdam (Germany) Yuri Shprits found out where and how these particles arise. To do this, they studied in detail how the plasma density changed at different points of the radiation belts, observing them for several months.
It turned out that the concentration of charged particles at different times could sharply increase or decrease. Comparing the data obtained with how often and where the beams of high-energy electrons appeared, physicists found that clusters of very rarefied plasma always formed before these events. Syringe and his colleagues calculated how the particles would behave in such conditions.
A sharp decrease in the plasma density markedly increased the efficiency of the “chorus”, allowing it to accelerate slowly moving electrons to energies above 7 MeV. The fraction of particles with such a high energy was relatively small, but they were quite enough to explain the data of the Van Allen probes and other devices that study the Earth’s magnetosphere.
Scientists suggest that similar processes can occur in the vicinity of other planets with powerful magnetic fields, such as Jupiter or Saturn. Their existence must be taken into account when preparing and sending missions that periodically fly through the radiation belts of these objects, the researchers concluded.
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