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April 14, 2024

Probes discover radiation belt around the Earth

By Mo-Yu Zhou | March 14, 2013

It has long been known that there are two radiation belts — the inner and outer belts — surrounding our planet. Recently, however, NASA’s Van Allen Probes mission brought to light a third radiation belt, an important discovery that goes to show that even the supposedly best-understood theories may need amending.

Radiation belts, discovered by and named after James Van Allen, are crucial to modern life. Solar storms and space weather can wreak havoc on Van Allen belts, causing them to swell intensely. As result of these threats, these areas can be hazardous to communications and GPS satellites — and humans in space.

Daniel Baker, a researcher from the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado in Boulder and lead author of the study, explained in an email interview with The News-Letter that these radiation belts are comprised of very high energy particles in space that are confined within the extended magnetic field surrounding our planet. Van Allen belts were first discovered 55 years ago, back when only two such regions of trapped radiation were observed.

The twin Van Allen Probes, launched last August 30, are the first dual-spacecraft mission to fly through these radiation belts. The particle detection instruments on board allowed scientists to observe radiation belts in unprecedented detail, bringing to sharper focus the processes and structures within these belts. These technological enhancements will potentially improve our understanding of the ways that the belts change in response to solar activity and the effects these changes might have on some parts of the Earth’s atmosphere.

These particle detection instruments aboard the probes are known as the Energetic Particle, Composition, and Thermal Plasma Suite (ECT). Part of this suite is the Relativistic Electron Proton Telescope (REPT) instrument, which generated the high-resolution images leading to the exciting discovery of the third belt. Baker believes the most challenging part of this study has been the development of these instruments.

“Leading up to the launch and discovery of the new features of the radiation belts, the most challenging things have been to design, develop, test and integrate such advanced and beautiful detection instruments,” Baker said.

For 55 years, it was believed that there are two Van Allen belts with a stable inner zone and a dynamic outer zone. The gap between them is called the “slot” region. Previously, observations of the outer belt could only be resolved as only a blurry image.

But an exciting revelation came just days after the launch of the probes, as its high-resolution particle detection instruments allowed scientists to clearly observe the existence of a previously unknown, third transient radiation belt, in addition to two slot regions. These findings were published in the February 28 edition of Science, and emphasize the changing and dynamic nature of these belts.

“This suggests that the very first discovery of the Space Age needs to be thoroughly revisited,” Baker added.

When REPT was turned on, powerful acceleration of electrons allowed scientists to see the new belt and slot region for four weeks before the sun sent an interplanetary shock wave and annihilated it.

The findings have important implications for the operation of spacecraft and space weather and its effects on Earth. There is also more left to be discovered.

“We need to use the kind of ‘active experiment’ that the Sun performed for us in September 2012 to better understand how particles in space are accelerated, transported and eventually lost from the Van Allen belts,” Baker said. “Even topics we thought were thoroughly understood for decades still can surprise us.”

The scientists involved in this study came from a wide variety of institutions, including LASP; NASA’s Goddard Space Flight Center; Los Alamos National Laboratory; the Institute for the Study of Earth, Oceans and Space at the University of New Hampshire; and the Applied Physics laboratory. This is the second mission of NASA’s Living With a Star Program, which aims to explore aspects of the solar system that have a direct impact on human life and society.


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