LASP instrument discovers a third radiation belt around Earth

Data collected from the LASP-built instrument, pictured here before its integration with the Van Allen Probes mission, has revealed a third radiation belt encircling Earth. (Courtesy JHUAPL)

The Van Allen Probes mission has revealed a third radiation belt encircling Earth, dispelling a long-held theory that only two of these hazardous charged particle layers exist in Earth’s magnetic field. This discovery is based on data collected from the LASP-built Relativistic Electron-Proton Telescope (REPT) experiment, published today in the journal Science online, at the Science Express website. A televised NASA press conference held at 12 noon MST featured LASP Director and lead author of the report, Dan Baker.

The twin Van Allen Probes satellites were launched in August 2012 to study the dynamics of Earth’s radiation belts and improve scientists’ ability to predict space weather. From September 1 to early October, 2012, the mission’s REPT sensors returned data that signified the emergence of a previously unseen middle belt, or “storage ring” of charged particles. The emergence was associated with a powerful electron acceleration event within the belts during this time.

In reference to the surprising results, Baker said, “It was so odd looking, I thought there must be something wrong with the instrument. But we saw things identically on each of the spacecraft. We had to come to the conclusion that this was real.”

On October 1, 2012, the new storage ring disappeared abruptly, most likely related to changes in the solar wind and a geomagnetic storm.

Earth’s belts are made up of trapped, highly energetic protons and electrons that can damage sensitive spacecraft electronics—including those responsible for weather monitoring and prediction, navigation, and communications—and that can harm astronauts passing through the belts during manned missions. The LASP-built REPT instruments measure the intensity, acceleration, number, and direction of these radiation particles.

For more information on the Van Allen Probes mission, previously known as the Radiation Belt Storm Probes (RBSP) mission, please visit

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