Radiation belts are zones of intense radiation surrounding a planet. They are found around Earth, Jupiter, Saturn, Uranus and Neptune. The Earth’s radiation belts were discovered in 1958 by James Van Allen using data from the Explorer 1 satellite.
The particles that make up the radiation belt come from the solar wind and other sources such as volcanoes on Io, a moon of Jupiter. They become trapped in the planet’s magnetic field. The particles are accelerated to high energies by interactions with the magnetic field. This makes them harmful to spacecraft and astronauts.
There are two main types of radiation belt: the inner zone and the outer zone. The innermost part of Earth’s radiation belt is called the Van Allen Belt after its discoverer, James Van Allen. It extends from about 1 000 km to 50 000 km above Earth’s surface. The outermost part is called the Trapped Radiation Zone or TRZ for short. It begins at about 60 000 km and can extend outwards to several million kilometers. There is also a third type of zone called the South Atlantic Anomaly (SAA) which is located over Earth’s South Atlantic Ocean near Brazil at an altitude of about 12000km – 16000km.
The amount of radiation present in a particular zone varies depending on factors such as solar activity and planetary orientation relative to the Sun (called “solar wind”). For example, during periods of high solar activity, more charged particles are ejected from the Sun which increases levels of radiation in all three zones mentioned above