NASA | Van Allen Probes Reveal Previously Undetected Radiation Belt Around Earth

These two nearly identical spacecraft launched in August 2012 and with only six months in operation, they may well be rewriting science textbooks. The probes study the Van Allen belts, gigantic radiation belts surrounding Earth, which can swell dramatically in response to incoming energy from the sun, engulfing satellites and spacecraft and creating potential threats to manned space flight.

James Van Allen discovered the radiation belts during the 1958 launch of the first successful U.S. satellite. Subsequent missions have observed parts of the belts, but what causes the dynamic variation in the region has remained something of a mystery.