NASA Probes Reveal Current In Earth's Radiation Belts Is Not As Expected

Visualization of the radiation belts with confined charged particles (blue and yellow). NASA/Goddard/Scientific Visualization Studio

Thanks to its strong magnetic field, Earth is protected from solar wind by regions of charged particles, the Van Allen belts. These energetic protons form an electric current that rings our planet, and thanks to new research we now understand how these particles behave.

Scientists from John Hopkins University have discovered that high-energy protons consistently inhabit the ring, but the variation in the intensity of the current depends on the arrival of lower energy protons during geomagnetic storms.

The results, published in Geophysical Research Letters, change our understanding of the ring current, which surrounds our planet between 10,000 and 60,000 kilometers (6,200 and 37,300 miles). The researchers believe that the discovery will make the space environment around Earth safer.

During the more quiet times when there's little solar activity and no geomagnetic storms, high-energy protons carry a large electrical current around the belt. But when solar storms hit, a substantial amount of low energy protons enters the ring, enhancing the current. 

Top Image is how the ring current looks normally with high energy protons highlighted in orange, but when there's a geomagnetic storm an influx of low energy protons (in magenta) enters the ring current. Johns Hopkins APL

“We study the ring current because, for one thing, it drives a global system of electrical currents both in space and on Earth’s surface, which during intense geomagnetic storms can cause severe damages to our technological systems,” said lead author of the study Matina Gkioulidou in a statement.

The current is part of the Van Allen belts, which are donut-shaped distributions of energetic charged particles trapped above Earth. This study is another indication that the belts are a lot more complex than we previously thought.

The discovery was possible thanks to NASA’s Van Allen Probes, two identical spacecraft orbiting Earth in a highly elliptical orbit. In particular, they used an instrument called RBSPICE, which measures both the composition – protons and other ions – and the pressure of the ring current.

“After looking at one year of continuous ion data it became clear to us that there is a substantial, persistent ring current around the Earth even during non-storm times, which is carried by high-energy protons,” Gkioulidou said. “During geomagnetic storms, the enhancement of the ring current is due to new, low-energy protons entering the near-Earth region. So trying to predict the storm-time ring current enhancement while ignoring the substantial preexisting current is like trying to describe an elephant after seeing only its feet.”

Understanding the exact nature and variation of energetic particles in the ring current and the Van Allen belts is paramount to protecting astronauts, satellites, and spacecraft in high altitude around our planet. 


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