Mysterious Third Radiation Belt Around Earth
June 21, 2013

Study Looks At How A Third Radiation Belt Appeared Around Earth

April Flowers for - Your Universe Online

Scientists have long believed that the Van Allen radiation belts, discovered in the Earth’s upper atmosphere in 1958, consisted of two doughnut-shaped rings of highly charged particles. The inner ring is comprised of high-energy electrons and energetic positive ions, and the outer ring of high-energy electrons.

This past February in the journal Science, however, a team of scientists reported the surprising discovery of a third, narrow radiation belt, which had briefly circled the Earth between the inner and outer rings in September 2012 during a magnetic storm. The third belt then almost completely disappeared in October during another magnetic storm, which has puzzled scientists more.

A new study led by the radiation belt group in the UCLA Department of Atmospheric and Oceanic Sciences describes the development and decay of this third belt in just over four weeks. The study findings are available online in the journal Geophysical Research Letters.

The team, led by UCLA professor of atmospheric and oceanic sciences Richard Thorne, performed a "quantitative treatment of the scattering of relativistic electrons by electromagnetic whistler-mode waves inside the dense plasmasphere," to account for the "distinctively slow decay of the injected relativistic electron flux.” This allowed the team to demonstrate why this unusual third radiation belt is observed only at energies above 2 mega-electron-volts. The data analyzed by the team was collected by the REPT instrument aboard the Van Allen Probes.

The primary mission of NASA’s Van Allen Probe Mission, formerly known as the Radiation Belt Storm Probes, is to understand the processes that control the formation and ultimate loss of such relativistic electrons. This research has important practical applications because of the enormous amounts of radiation generated by the Van Allen belts pose significant hazards to satellites and spacecraft, as well as to astronauts performing activities outside the protection of a spacecraft.

The Van Allen Probes are twin spacecraft with nearly identical eccentric orbits, which cover the entire radiation belt region of the upper atmosphere. The two spacecraft lap each other several times over the course of the mission, which started in 2012.