Van Allen Belts

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Van Allen Belts is the name given to plasma trapped in the Earth’s magnetic field. It is mainly made up of electrons and protons and a few others like Helium nuclei (alpha particles). There are actually two main belts. The outer one is made up of high energy electrons, while the inner one is mainly made up of electrons and protons.

The energetic charged particles are actually bi-products of constant cosmic radiation bombardment on the Earth’s atmosphere. During bombardment, ions, electrons, and protons, are scattered in all directions like billiard balls.

Some proceed to the Earth’s surface, others are ejected to outer space, while there are those that end up trapped in the magnetic field of the Earth. The magnetic field exerts forces on them (and confines them) because of the presence of their charges.

In some cases, the bombardments also produce neutron fragments, which have zero charge. Having no charge, the neutrons don’t interact with the magnetic field. However, since these neutrons are highly unstable as a result of the high-energy collisions they just emerged from, they eventually decay. Among their bi-products are positively charged protons.

The protons are the ones that then end up trapped. These protons make up a fraction of the inner belt.

The electrons that comprise the outer belt, on the other hand, are believed to originate from geomagnetic tail following geomagnetic storms.

The Van Allen Belts are supposed to take a torus shape. However, due to the presence of solar winds on one side (the one facing the Sun), the belts are compressed there, and somewhat stretched on the other side.

The Van Allen Belts were named after James Van Allen, who confirmed the presence of the inner radiation belts in 1958. He was able to do this with the aid of Explorer 1 and Explorer 2, two artificial satellites that he helped design. Similar radiation belts are found in other planets. However, they aren’t called Van Allen Belts. This name is only used for the earth-bound ones.

The region occupied by this trapped plasma is very huge, up to 7 Earth radii. The innermost surface of the plasma begins at about 200 km from the Earth’s.

Solar cells, sensors, as well as integrated circuits can be damaged when passing through these trapped high energy charged particles. As such, spacecrafts and their components are shielded for protection. The Hubble Telescope, for example, usually shuts down its sensors when passing through the belts.

Because of the hazards the trapped plasma poses to space missions, some scientists are suggesting that moves be made to drain them of their current magnitude.

We have some related articles here in Universe Today. Here are the links:

• Jupiter has Van Allen Belts too, Just Bigger; Implications for Space Weather Prediction
• Van Allen Safe Zone Migrates

Here are the links of two more articles from NASA:

• The Van Allen Belt
• The Radiation Belts

Here are two episodes at Astronomy Cast that you might want to check out as well:

• Avoiding the Heat Death, Orbiting Galaxies, and the Dangers of Space Radiation
• The US Space Shuttle

References:
NASA: The Van Allen Belt
NASA: Radiation Belts

Tagged as: earth magnetic field, magnetic field, plasma, radiation belts, Van Allen Belts