This post’s subject will be the Van Allen belts. Why I will talk about something from space in the environment topic? Because the magnetosphere which created these belts protects Earth against dangerous solar winds and space radiation, therefore protects life on Earth.
The belts
Are made of particles captured and accelerated by Earth`s magnetic field and have a toroid shape (donut). There are two Van Allen belts. An inner (the red one in the figure below) goes from 600 to 10000 km of altitude and an outer (grey in the figure) goes from 13000 to 65000 km of altitude.
The inner belt has protons with high energy from 10 to 100 MeV (mega electron-volt). Electron-volt is a measuring unit very used in particle physics, 1 eV is the kinetic energy an electron has when accelerated by a voltage of 1 V in a vacuum.
1eV=1\times 10^{-19} J (Joules)
The outer belt has electrons, alfa particles, and ions, with energy from 10 keV to 10 MeV. The belts can change shape depending on energy and electron distribution. The inner belt is more stable than the outer.
The 1 is the belt’s default shape. The 2 appear when there are electrons with energy above 1 MeV, in this state was observed only electrons are in the outer belt. When electrons stay with energy below 0,1 MeV, the inner belt stays much larger like in 3. The 4 happens during geomagnetic storms, when the Sun emits a great quantity of charged particles, the empty space is filled with low-energy electrons. In some cases, the belts don’t change shape during geomagnetic storms. The behavior due to space conditions isn’t fully understood yet.
Space missions
This belt is a great obstacle to space missions. The particles in the belts are a great danger to the crew and electronic devices. The international space station stays at 400 km of altitude.
Recently it was discovered that low frequency radio waves (VLF) artificially made created a barrier against particles from the inner belt. Maybe a spaceship that emits VLF can pass through the Van Allen belts and be protected against radiation.
