Two doughnut-shaped belts of high-energy charged particles trapped in Earth’s magnetic field; they were discovered in 1958 by James Van Allen based on measurements made by Explorer 1. The inner Van Allen Belt lies about 9,400 km (1.5 Earth radii) above the equator, and contains protons and electrons from both the solar wind and the Earth’s ionosphere. The outer belt is about three times further away and contains mainly electrons from the solar wind.
