Two regions of radiation encircle the Earth. They’re called the Van Allen belts, and they are a pair of dynamic regions of trapped radiation, separated by a void and held in place by the Earth's magnetic field. They protect the planet from the radiation of space and the effects of solar weather.
We’ve known about these two belts since James Van Allen, the eponymous astronomer, discovered them in 1958. It's important that we know as much as we can about the Van Allen belts and how they change, because most of Earth's satellites live in the region.
Two NASA probes detected a third radiation belt, which disappeared a few weeks later. It appears that solar weather caused its formation, and disappearance.