Ray Belt: Mystery of vanishing electrons solved

Measurements in the solar storm settle previous dispute of the theories

Magnetosphere of the Earth (blue) with the Van Allen belts. The colors mark zones with energetic particles. © Martin Rother / GFZ
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Enigmatic electron loss: researchers have solved a decade-old puzzle of the Van Allen Belt. Because they finally found out where the fast electrons of these ray belts disappear in a solar storm. The surprising result: Both previously competing theories are correct - one applies to slow, the other for ultrafast electrons, as the researchers in the journal "Nature Communications" report.

They are our life-saving shield: Earth's magnetic field and Van Allen belts shield us from much of the high-energy radiation and particles from space. Even in a solar storm, they ensure that a large part of it is intercepted. But then, in the Van Allen belts of the earth, extremely fast electrons race around the earth like in a huge ring.

Riddles of "Drop-outs"

However, one phenomenon has been puzzling researchers for decades: the so-called "drop-outs". If a strong solar storm hits the earth, it can temporarily cause a dramatic fading of ultrafast electrons in the Van Allen Belt. Their density drops by a thousand times within an hour.

But why? So far there have been two contradictory theories. After one of them, huge electromagnetic waves in the ray belt cause the electrons to be deflected down into the earth's atmosphere. The competing theory assumes that the electrons are not deflected down, but upwards and disappear into space.

In a solar storm, plasma and high-energy radiation are thrown far into space NASA / Solar Dynamics Observatory

Both are right

A solar storm on 17 January 2013 has now helped Yuri Shprits of the German Research Center for Geosciences GFZ in Potsdam and his colleagues to resolve this contradiction. "The storm offered ideal conditions, " explains Shprits. For NASA's Van Allen spacecraft was in the right place to closely observe the behavior of the electrons in the Van Allen belt. display

The evaluation of the data revealed surprising: Both theories are right. The decisive factor for the disappearance of the electrons is how fast the individual particles are. Ultrarelativistic electrons, which fly at up to 99 percent of the speed of light, are thus actually diverted from the waves into the atmosphere. But with the somewhat slower relativistic electrons, the second mechanism works: they are deflected into the interplanetary space.

This is an old research question, says Shprits. At the same time, knowing about these processes now offers better ways to understand processes in our radiation belt, but also around other planets. "Our results will also help to better predict the 'space weather' and thus protect valuable satellites, " says the researcher. (Nature Communications, 2016; doi: 10.1038 / ncomms12883)

(German Research Center for Geosciences GFZ, 04.10.2016 - NPO)