An artist's concept of the Van Allen radiation belts surrounding Earth. The blue, concentric shells represent the inner and outer belts. Researchers have recently proven the existence of a concentration of antimatter in these belts. Credit: NASA's Conceptual Image Lab/Walt Feimer

Antiprotons trapped in Earth’s inner radiation belt have been observed for the first time by the PAMELA satellite-borne experiment. According to the study, these antiparticles are produced in nuclear interactions of energetic cosmic rays with the terrestrial atmosphere and accumulate in the geomagnetic field at altitudes of several hundred kilometers above Earth’s surface.

The satellite, named Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics, was launched in 2006 to identify high-energy particles that arrive as cosmic rays from the Sun and beyond the solar system which barrel into Earth. Results obtained from this space-borne experiment have allowed scientists to test transport models in the terrestrial atmosphere, a move that has reduced uncertainties concerning the antiproton production spectrum in Earth’s magnetosphere.

The antiparticle population originates from cosmic ray interactions in the upper atmosphere and subsequent trapping in the magnetosphere. The PAMELA data confirm the existence of a significant antiproton flux below 1 GeV in kinetic energy: The kinetic energy range in the South Atlantic Anomaly has been measured at 600 to 750 MeV. This flux exceeds the galactic cosmic ray antiproton flux by three orders of magnitude at the current solar minimum. According to the authors of the study, who hail primarily from research institutions in Italy, this ring of antimatter is the most abundant antiproton source near the Earth.


The PAMELA experiment, prior to launch.

The discovery of geomagnetically trapped cosmic ray antiprotons

The PAMELA mission