The Van Allen Belts

VanAllenProbes Decal2012_4PrintOur planet’s magnetic field holds a torodial band of radiation in a belt around Earth. These Van Allen Belts protect us from solar eruptions, growing and shrinking as they are excited. On November 2014, astronomers announced in the journal Nature, they had found an impenetrable barrier within the Belts that prevents the most energetic particles – so called ‘killer electrons’ that can threaten astronauts and spacecraft – from reaching Earth. “It’s almost like these electrons are running into a glass wall in space,” says Daniel Baker of the University of Colorado, Boulder, who was the lead author on the study. “Somewhat like the shields created by force fields on Star Trek that were used to repel alien weapons, we see an invisible shield blocking these electrons. It’s an extremely puzzling phenomenon.”

radiation1From the time James Van Allen discovered the Earth-girdling radiation belts that bear his name in the 1950s, their structure has seemed stable and settled: two nested toroidal whirlpools of particles, with an inner belt of high energy electrons and protons circulating 1600 to 13000 kilometers above the surface; an outer belt consisting primarily of electrons boiling at altitudes of 19,000 to 40,000 km; and a separating, low-energy “slot.” The structure might throb and pulse a bit in the solar wind, but it otherwise seemed as solid and reliable as the moon, and can stretch to some 25,000 miles (40,000km). This newly discovered barrier sits at some 7,200 miles (11,600km). “The textbooks always said two Belts, and here we have three Belts,” Baker said.

Credits: Astronomy.