The Van Allen Belts

Written by Andrew Clark, IGES

On January 31, 1958, America launched its first Earth satellite. Explorer-1, equipped with a cosmic-ray detector, made a tremendous, unexpected discovery- the presence of a belt of charged particles trapped in space by the Earth’s magnetic field.

Theorized by Dr. Van Allen, this particle belt was confirmed to exist by Explorer-3 later that same year. The study of the Van Allen belt continues to this day. We have learned much – there are actually two belts, an inner and an outer belt. We’ve also learned that these Van Allen belts are dynamic- growing or shrinking in size in response to solar weather.

When the belts expand they have a higher likelihood of exposing satellites orbiting Earth to unwanted radiation, which is a concern for these satellites as well as spacecraft and space travelers traveling through these regions away from Earth.

The most recent discovery about the Van Allen belts (by the current Van Allen Probes) is that the high energy electrons in the outer Van Allen belt that move in circles around the Earth cannot move in towards earth past a certain point. Previously it was thought that these electrons could easily move into the space towards Earth between the inner and outer belts. Instead, these high energy electrons are held in place by interactions with lower energy electrons in the plasmasphere.

As you can see, the first discovery by an Earth satellite cascaded into numerous discoveries and relies on and is supported by research in different fields. Introduce your students to these topics and who knows what they might discover for themselves!