What Is a Van Allen Radiation Belt?

Van Allen Radiation Belts are two zones encircling the low Earth orbit in which there are relatively large numbers of high-energy (fast-moving) charged particles. The particles are mainly protons and electrons, which are trapped within the belts by Earth's magnetic field.

A group of United States scientists, under the direction of Dr. James Van Allen, made the discovery in 1958, using information from Explorer I, America's first artificial satellite. When the team first discovered the belts, "the radiation was so intense that at first scientists thought they might be recording a Soviet nuclear test," according to NASA.

Van Allen learned that astronauts could safely fly through the radiation belts if they went through weaker regions. The Van Allen belts are centered along Earth's magnetic equator in a region of the upper atmosphere called the magnetosphere, or exosphere.

Radiation belt electrons are highly energetic electrons that are confined within the Earth's radiation belts:

Scientists believe most of the particles that form the belts come from the solar wind, a continuous flow of particles emitted by the sun in all directions. Other particles probably have their origin in cosmic rays.

In the late 1950s and early 1960s, artificial radiation belts formed from charged particles produced by the detonation of nuclear explosives in space. These radiation belts, however, have weakened with time. The planets Jupiter and Saturn are encircled by radiation belts similar to the Earth's Van Allen radiation belts.

The Van Allen Belts and the Moon Landing

To travel to outer space, astronauts must pass high levels of radiation. For some, the existence of Earth's radiation belts is proof that we never landed on the moon. They argue that the level of radiation would have "instantly killed" the astronauts.

NASA says that astronauts "fly through this region quickly to limit their exposure to radiation" and that a deadly amount of radiation is 300 rads in one hour. The crew for the Apollo moon landing's radiation dosimeters measured "their total dosage for the entire trip to the moon and return was not more than 2 Rads over 6 days."

The inner and outer Van Allen Belt resemble donuts. They protect the Earth from solar wind and solar storms.

Both belts can expand and contract, but the inner Van Allen belt is more stable than the outer electron radiation belt. Their movement can affect the more than 800 satellites that exist within the belts, making it crucial for us to know more about how the belts work so we can protect these satellites.

In 2013, researchers announced an intriguing discovery: a temporary third radiation belt caused by high-energy electrons. While this third belt is short-lived, it adds another layer of complexity to the Van Allen Belts' behavior.

Scientists were able to detect the third ring because of NASA's Van Allen Probes, formerly known as the Radiation Belt Storm Probes. The goal of the probes is to gain a better understanding of space weather before it affects the Earth. The probes showed that for a month in September 2012, there was an outermost third belt, which inspired scientists to change their approach.

"The Van Allen Probes' observations challenged our current views on the physics of the radiation belts," said space scientist Yuri Shprits. "In the past, we made estimates and thought they looked reasonable. Now we know we need to understand each storm in much more detail, creating global models that can reconstruct what's happening at every level."

The Relativistic Electron Proton Telescope

The Relativistic Electron Proton Telescope (REPT) is an instrument designed to study the energetic particles, specifically electrons and protons, within the Earth's radiation belts. It is one of the scientific instruments aboard the Van Allen Probes.

REPT measures and characterizes the energetic electrons and protons within the Van Allen Belts. These particles are a critical component of the radiation belts, and studying their properties is essential for understanding the dynamics and behavior of the belts.

For space exploration missions, understanding the Van Allen Belts is crucial. Spacecraft must navigate these regions, and the belts' radiation can affect spacecraft systems and instruments. Scientists and engineers work to design spacecraft that can withstand the challenges posed by the belts.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.