The earth is surrounded by a multi-part ring of high-energy particles and rays, the so-called Van Allen Belt. It arises because the Earth’s magnetic field captures particles of the solar wind and directs them into orbits around the Earth.
Portions of this shell act like a plasma shield that prevents high- energy particles from penetrating into deeper layers. Some time ago researchers discovered enigmatic patterns in the plasma in the inner area of this belt caused by the different density of the orbiting electrons – they look like zebra stripes. First models suggested that they are formed by a resonance effect between the drift of the electrons and the electromagnetic field of the earth.
The exact structure of these strips remained unclear until Cleo Loi of the University of Sydney and her colleagues studied the strips with the help of the Murchison Widefield Array (MWA) – in Western Australia, two years ago. The result of the study appeared in the journal “Geophysical Research Letters” .
The crosswalks turned out to be gigantic plasma tubes
The radio telescope used consists of 128 sub-antennas and can create very fast consecutive shots. This made it possible for the scientists to even record the temporal changes of the plasma stripes.
“We saw a striking pattern in the sky, where strips of high-density plasma alternated with less dense strips,” the science magazine “sciencexx” Loi quotes . “This pattern drifted slowly, following the lines of Earth’s magnetic field – almost like a polar light.”
After watching the mysterious crosswalks more closely, the researchers turned out to be plasma tubes. These are gigantic curved tubes that can be seen far above the earth’s surface in the sky. “For more than 60 years, researchers have suggested that these structures exist – for the first time, we have made them directly visible,” says Loi.
“The discovery of the structure is important because it causes unwanted signal interference. These could, for example, affect our civil and military navigation systems, which are satellite based. So we have to understand the tubes, “writes Loi on the website of the University of Sydney .
With the telescope, the scientists were able to capture and analyze the three-dimensional structure of these plasma stripes for the first time. For this they processed the signals of the westernmost and easternmost antennas separately, so that the very small parallax shift shed light on the spatial depth.
“It’s like turning the telescope into a pair of eyes,” Loi explains. “This allowed us to pinpoint the distance between the strips, their height above the ground and their inclination – that was not possible before.”
The plasma tubes are located in about 600 kilometers in the upper ionosphere , but they extend up into the plasmasphere. In addition, their arrangement is surprisingly regular, because they follow the field lines of the earth’s magnetic field.
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