The zones of energetic charged particles trapped by the Earth's magnetic field, surrounding the planet, are called the:

The Van Allen belts are two doughnut-shaped zones of high-energy charged particles, mainly protons and electrons, held in place around the Earth by its magnetic field.

Discovery:

• The belts were discovered in 1958 by the American physicist James Van Allen.
• Instruments he designed, flown on Explorer 1 and Explorer 3, the first successful American satellites, detected unexpectedly high levels of radiation.
• The belts were the first major scientific discovery of the space age.

Structure:

Inner belt: lies roughly 1,000 to 6,000 km above the Earth. It contains mainly high-energy protons, produced when cosmic rays strike the upper atmosphere.

Outer belt: lies roughly 13,000 to 60,000 km above the Earth. It contains mainly high-energy electrons, largely supplied by the solar wind.

In 2013, NASA's twin Van Allen Probes found that a third, temporary belt can sometimes form.

Why the particles are trapped:

• The Earth's magnetic field acts like a magnetic bottle.
• Charged particles spiral along the magnetic field lines and bounce back and forth between the northern and southern hemispheres.

Importance:

• The belts, and the magnetic field that holds them, help shield the Earth from much of the harmful solar wind and cosmic radiation.
• But the radiation in the belts is dangerous for spacecraft electronics and astronauts.
• Satellites are designed with shielding, and many avoid staying long in the most intense regions.

Related phenomena:

During solar storms, charged particles can enter the upper atmosphere near the poles and produce the aurora borealis (northern lights) and aurora australis (southern lights).

Why not the other options?

• ✗The Kuiper Belt is a region of icy bodies beyond the planets.
• ✗The ozone layer, in the stratosphere, absorbs ultraviolet radiation from the Sun.
• ✗The ionosphere is a layer of the upper atmosphere containing ions, which reflects radio waves.