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Antimatter close to home

An anomaly in the south Atlantic, apparently

As anyone who follows big physics knows, the best way to trap anti-matter is with a magnetic field: that way, you can prevent the mutual annihilation that results from interactions with normal matter.

Usually, you need a particle accelerator and a big magnet to grab hold of antimatter, even for a fraction of a second. However, according to a paper published in The Astrophysical Journal Letters, the Earth’s magnetic field will do just as well.

The paper, to be published on August 20, suggests that a thin band of antiprotons has been observed in the Van Allen belt surrounding the Earth. The Van Allen belt is a torus of ionized particles – from sources like the solar wind and cosmic rays – trapped by Earth’s magnetic field.

The team of more than 60 researchers identified signs of antiprotons in the Van Allen belt using data from the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (Pamela) satellite.

One of the co-authors of the work, Alessandro Bruno, told the BBC the belt is “the most abundant source of antiprotons near Earth”.

Most of the antimatter produced when cosmic rays strike the outer atmosphere are too close to survive, instead colliding with normal matter and annihilating in a burst of energy. However, the Pamela data found that in a region known as the South Atlantic Anomaly, the satellite spotted a far greater concentration of trapped antiprotons.

Many of these still encounter the atmosphere, but above altitudes of several hundred kilometers, Bruno says many more survive to be trapped in the Van Allen belt.

Indulging, perhaps, in a bit of sci-fi crystal ball gazing, Bruno hypothesized that the antiprotons may be plentiful enough to power spacecraft of the future. ®

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