Third radiation belt discovered around Earth

NASA’s Van Allen Probes find a new radiation belt around our planet.


In 1958, two gigantic loops of radiation, known as Van Allen Belts, were discovered by the very first launches of satellites. Today’s observations show that a third belt can sometimes appear.

Just when we thought we knew the radiation environment that loops around our planet, a third has made itself known to NASA’s Van Allen Probes; dual spacecraft which, since their launch in August last year, have doggedly endured the bombardment of harsh space weather as they dive through the radiation trapped in Earth’s magnetic field.

Named after their discover James Van Allen of the University of Iowa, who confirmed their existence using the Explorer 1 and Explorer 3 missions, the Van Allen radiation belts are doughnut-shaped layers of energetic charged particles, or plasma. Held in place by the Earth’s magnetic field, the outer ring consists mainly of high energy electrons that vary in intensity, depending on the strength of the solar wind, over a timescale of hours to days. The inner belt, on the other hand, is crammed with a cocktail of energetic electrons and extremely excited protons.

The Van Allen belts extend around 1,000 to 60,000 kilometres (620 to 37,300 miles) above the Earth’s surface and swell dramatically in response to aggressive solar storms and intense space weather, posing danger to communications and GPS satellites as well as astronauts.

Speaking of the instruments aboard the Van Allen Probes that made uncovering the distinctive third belt possible – the Relativistic Electron Proton Telescope (REPT) and the Energetic particle, Composition and Thermal plasma suite (ECT) – lead scientist of the study Daniel Baker at the University of Colorado, says: “This is the first time we have had such high-resolution instruments look at time, space and energy together in the outer belt.”

“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 and the new slot between it and the outer belt,” adds Baker who is also the REPT instrument lead.

John Grunsfield, NASA’s associate administrator for science, states that the new capabilities, as well as the advances in technology in the probes, has allowed scientists from a mixture of institutions – including NASA’s Goddard Space Flight Center in Greenbelt, Los Alamos National Laboratory in Los Alamos and the Institute for the study of Earth, Oceans and Space at the University of New Hampshire in Durham – to peer into the unknown in unprecedented detail and grab an insight on just “how the radiation belts are populated with charged particles. [Hopefully] insight will be provided on what causes them to change, and how these processes affect the upper reaches of the Earth’s atmosphere.”

However, this new addition to our planet didn’t stick around for long. Thought to have been the result of the August 2012 solar prominence, a large, bright, gaseous feature that extends outward from the Sun’s surface in a loop, the third belt graced the Van Allen spacecraft with its presence for roughly four weeks before being destroyed by an interplanetary shockwave; a disturbance moving ahead of a coronal mass ejection event from the solar surface. These bursts of solar wind are often the result of prominences breaking apart.

Late August last year saw a ginormous prominence erupt from the surface of the Sun. Particles and a shock wave blasted the Earth and, is thought, to have caused the third radiation belt.

“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 the deputy project scientist of the Van Allen Probes Nicky Fox, who is currently at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. “We thought that we knew the radiation belts, but we don’t. The advances in technology and detection made by NASA in this mission already have had an almost immediate impact on basic science.”

The data returned by the pair of spacecraft are important for the study of the effect of space weather on Earth, as well as those observed around other astronomical objects that litter our Universe, such as planets and faraway nebulae.

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Images courtesy of NASA/Van Allen Probes/Goddard Space Flight Center/SDO/AIA

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