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NASA’s Van Allen Probes find third Radiation Belt around the Earth


Written by Dr. Tony Phillips
Science at NASA

NASA - National Aeronautics and Space AdministrationWashington, D.C. – Earth’s radiation belts were one of the first discoveries of the Space Age. A new finding published in today’s issue of Science shows that we still have much to learn about them. NASA’s twin Van Allen Probes, launched just last August, have revealed a previously unknown third radiation belt around Earth.

“Even 55 years after their discovery, Earth’s radiation belts still are capable of surprising us,” said Nicky Fox, Van Allen Probes deputy project scientist at the Johns Hopkins University Applied Physics  Laboratory in Laurel, MD. “We thought we knew the radiation belts, but we don’t.”

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Previous observations of the Van Allen belts dating back to the late 1950s have documented two distinct regions of trapped radiation surrounding our planet, known as the inner and outer radiation belts. Particle sensors aboard the twin Van Allen Probes quickly revealed to scientists the existence of a transient, third radiation belt.  Scientists observed the third belt for four weeks before a powerful interplanetary shock wave from the sun annihilated it.

Each of the two Van Allen Probes carries an identical set of five instrument suites that allow scientists to gather data on the belts in unprecedented detail. Key data for this discovery came from the Relativistic Electron Proton Telescope (REPT) instrument, part of the probes’ Energetic Particle, Composition, and Thermal Plasma Suite (ECT).

“This is the first time we have had such high-resolution instruments look at time, space and energy together in the outer belt,” says Daniel Baker, lead author of the study and REPT instrument lead at the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado in Boulder. “Previous observations of the outer radiation belt resolved it as a single blurry element. When we turned REPT on just two days after launch, we clearly saw the new belt and a [gap] between it and the outer belt.”

Back in the 1950s when the radiation belts were discovered, they had little effect on ordinary people. Today the radiation belts are crucial to our high-tech society.  Hundreds of satellites used for everything from weather prediction to GPS to television routinely skim the belts, subjecting themselves to energetic particles that can damage solar panels and short-circuit sensitive electronics.  During geomagnetic storms when the belts are swollen by solar activity, whole fleets of satellites can be engulfed, imperiling the technological underpinnings of daily life on the planet below. The Van Allen Probes directly address these down-to-Earth problems

“The fantastic new capabilities and advances in technology in the Van  Allen Probes allow scientists to see in unprecedented detail how the radiation belts are populated with charged particles, what causes them to change, and how they affect the upper reaches of Earth’s atmosphere,” says John Grunsfeld, NASA’s associate administrator for science in Washington DC.

For more information about the Van Allen Probes, visit

More Information and Credits

Observations of the new belt were made by scientists from institutions including LASP; NASA’s Goddard Space Flight Center in Greenbelt, MD; Los Alamos National Laboratory in Los Alamos, NM; and the Institute for the Study of Earth, Oceans, and Space at the University of New Hampshire in Durham.

The Van Allen Probes are the second mission in NASA’s Living With a Star Program to explore aspects of the connected sun-Earth system that directly affect life and society. Goddard manages the program. The Applied Physics Laboratory built the spacecraft and manages the mission for NASA.

The Van Allen Probes were originally known as the Radiation Belt Storm Probes.  They were later re-named after the discoverer of the belts, James Van Allen.  A Sciencecast video introduces the mission




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