Earth’s new radiation belt

Print edition : March 22, 2013

NASA’S Van Allen Probes mission has discovered a previously unknown third radiation belt around the earth, revealing the existence of unexpected structures and processes within these hazardous regions.

For long, it has been known that the Van Allen belts have two distinct regions of trapped radiation surrounding the planet. Unexpectedly, within days of the launch on August 30, 2012, particle detection instruments aboard the twin Van Allen Probes revealed the existence of this new, transient, third radiation belt.

The belts, named after James Van Allen, who discovered them in 1958, are critical regions for many space-based technologies. They are affected by solar storms and space weather and can swell dramatically. When this occurs, they can pose a danger to communications and GPS satellites as well as humans in space. The data from the mission are important for the study of the effect of space weather on the earth.

The advanced capabilities of the instruments aboard the Van Allen Probes have allowed scientists to see in unprecedented detail how the radiation belts are populated with charged particles. This discovery shows the dynamic and variable nature of the radiation belts and improves our understanding of how they respond to solar activity. The findings, published in the latest issue of Science, are the result of high-resolution observations by the Relativistic Electron Proton Telescope (REPT) instrument, part of the Energetic Particle, Composition, and Thermal Plasma Suite (ECT) aboard the Van Allen Probes. They reveal that there can be three distinct, long-lasting belt structures, with the emergence of a second empty slot region, or space, in between. “This is the first time we have had such high-resolution instruments look at time, space and energy together in the outer belt,” said Daniel Baker, lead author of the study at the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado in Boulder. “Previous observations of the outer radiation belt only resolved it as a single blurry element. When we turned REPT on, just two days after launch, a powerful electron acceleration event was already in progress, and we clearly saw the new belt.”

Scientists observed the third belt for four weeks before a powerful interplanetary shock wave from the sun annihilated it. “Even 55 years after their discovery, the earth’s radiation belts still are capable of surprising us and still have mysteries to discover and explain,” said Nicky Fox, Van Allen Probes deputy project scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, U.S.