The high radiation environment around our planet exists because charged particles become trapped in the Earth’s magnetic field; the same magnetic field that protects us from deadly radiation also prevents that radiation from dissipating into space. The particles just don’t have enough energy to escape. So the two belts are like two nested doughnuts circling the planet. Their altitudes vary slightly, but the inner doughnut sits between 600 and 3,700 miles above the planet and is comprised mainly of highly energetic protons. The outer doughnut, meanwhile, sits between 9,300 and 12,400 miles above the planet and is made of both protons and electrons. The radiation environments of both vary, more dense in some places and nearly absent in others.