Two radiation belts surrounding the Earth, containing trapped charged particles. The inner Van Allen Belt lies around 1.5 Earth radii (9400 km) above the equator, and contains protons and electrons of both solar and ionospheric origin. The outer Van Allen Belt, at an equatorial distance of 4.5 Earth radii (28 000 km), contains mainly electrons from the solar wind. The belts were discovered in 1958 by J. A. Van Allen from measurements obtained by the Explorer 1 satellite.