Scientists have discovered “stripes” of plasma waves inside Earth's magnetic field. The discovery of these plasma waves was first made in the 1960s, but at the time scientists could not explain how they formed.

Now, Yuri Shprits of the University of California, Los Angeles, and his colleagues at the University of Sheffield and elsewhere have used two European Space Agency (ESA) Cluster satellites to solve the mystery, the results of which are published in the journal Nature Communications. Two spacecraft, flying 60 kilometers (40 miles) apart, found 13 equally spaced lines that looked like a “zebra pedestrian crossing.”

Also known as “Russell noise,” named for the discoverer of the waves Christopher Russell, the waves appear to get their energy from protons in space, which may help accelerate electrons to very high energies. “It turns out they are generated by proton distributions,” Shprits told IFLScience.

The stripes of plasma were found about 19,000 kilometers (12,000 miles) from Earth’s surface and, crucially, they were found to be a multiple, or harmonic, of the frequency at which protons gyrate around Earth’s magnetic field lines. This means that it must be the protons that are giving these waves their energy. 

The stripes are important because they may indicate a region of space where new types of interactions are taking place. In particular, they may also play a part in accelerating high-energy electrons that can cause damage to satellites, spacecraft and even humans in space. The waves are moving slowly around Earth, being generated in and around our planet, and mostly around its equatorial plane.

“We have known since the 1960s that when satellites go over the equator, they see this noise,” Shprits told IFLScience. “We call this equatorial noise, because it’s very closely confined to the geomagnetic equator.” He added that it was surprising to find that the waves were “very structured and organised” in stripes like this.

The research could help develop protection measures against radiation in space, and may also explain more about how our planet interacts with the Sun.