Data from the cosmic ray satellite PAMELA has added substantial weight to the theory that the Earth is encircled by a thin band of antimatter.

The satellite, named Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics, was launched in 2006 to study the nature of cosmic rays — high-energy particles from the Sun and beyond the solar system which barrel into Earth.

When those cosmic rays smash into molecules in the Earth’s upper atmosphere, a shower of smaller particles is created. Physicists have assumed that a small number of those resulting particles will be anti-protons.

Most of those will be instantly annihilated when they collide with particles of ordinary matter. But those which don’t collide should get trapped in the Earth’s torus-shaped Van Allen radiation belt, and form a layer of antimatter in the Earth’s atmosphere.

It was one of PAMELA’s goals to hunt out those tiny numbers of antimatter particles among the ludicrously more abundant normal matter particles, like protons and the nuclei of helium atoms.

To find them, the satellite regularly moved through a particularly dense section of the Van Allen belt called the South Atlantic Anomaly. Over a period of 850 days — from July 2006 to December 2008 — sensors aboard PAMELA detected 28 anti-protons. That might not sound like much, but it’s three times more than would be found from a random sample of the solar wind, and is the most abundant source of anti-protons ever seen near the Earth.

But what does this discovery mean, other than proving that a bunch of theorizing physicists were correct? The discovery opens the doors to harnessing those anti-protons for a variety of medical, sensing and, most importantly, rocket-propelling applications.

In a 2006 NASA-founded study by Draper Laboratory, researchers wrote, “it has been suggested that tens of nanograms to micrograms of anti-protons can be used to catalyze nuclear reactions and propel spacecraft to velocities up to 100 km/sec.”

Image: Illustration of Earth’s Van Allen radiation belts. (NASA)

Source: Wired.co.uk

Citation: “The Discovery of Geomagnetically Trapped Cosmic-Ray Antiprotons.” O. Adriani et al. The Astrophysical Journal Letters, July 27, 2011. DOI: 10.1088/2041-8205/737/2/L29

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