Third radiation belt discovered around Earth

By Nick Collins, Science Correspondent

Since 1958 scientists have known that Earth is circled by two doughnut-like rings of trapped charged particles called the Van Allen radiation belts.

But now a third, temporary belt has been discovered after, appearing for a month last year before being dispersed by a shock wave released by the Sun.

Astronomers hope to discover how often the third belt forms and learn more about the behaviour of all three belts, which can damage communications and GPS satellites and expose astronauts to extra doses of radiation.

The Van Allen belts, named after their discovered James Van Allen, are known to periodically swell as a result of space weather and solar storms but the exact cause is poorly understood.

The new observations, published in the Science journal, were made by Nasa's twin Van Allen probes which were launched on August 30 bearing hi-tech particle detection equipment.

John Grunsfeld, NASA’s associate administrator for science, said: "The fantastic new capabilities and advances in technology in the Van Allen Probes have allowed scientists to see in unprecedented detail how the radiation belts are populated with charged particles and will provide insight on what causes them to change, and how these processes affect the upper reaches of Earth’s atmosphere."

The outer of the two Van Allen belts had previously been seen as one blurry ring, but high resolution images taken by the Relativistic Electron Proton Telescope instrument on board the probes revealed two separate rings with a clear space in between. The new belt was visible for four weeks before being destroyed by a shock wave released by the Sun.

Nicky Fox, Van Allen Probes deputy project scientist at the Johns Hopkins University, said: “We thought 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."