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Posts Tagged ‘PAMELA

Could Earth’s ring of antimatter power spacecraft?

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A belt of antimatter has been discovered circling the Earth, which in future could be used to fuel voyages that race at breakneck speeds to other planets in the Solar System.

Antimatter has properties that are opposite those of normal matter – for example the positive charge on a proton is negative in an antiproton. When antimatter and normal matter come into contact, they annihilate spectacularly, releasing energy. The Italian-run PAMELA (Payload Antimatter Matter Exploration and Light Nuclei Astrophysics) satellite, launched in 2006, has found thousands of times more antiprotons than expected in a region of the innermost Van Allen radiation belt called the South Atlantic Anomaly. The anomaly appears to be a concentrated region of a much larger antimatter belt, and is the point at which the innermost radiation belt is nearest the Earth’s surface (an altitude of about 500 kilometres) and Earth’s magnetic field lines, which confine the belts, are at their weakest.

An artist’s impression of an antimatter powered spacecraft. Such craft would be capable of making the round trip to Jupiter in just one year. Image: NASA.

James Bickford, the senior member of the technical staff at Draper Laboratory in Cambridge, Massachusetts, USA, has calculated that Earth’s antimatter belt contains 160 nanograms of antiprotons. This in itself doesn’t sound much – pure annihilation of this antimatter would produce just ten kilowatts of energy per hour – but it dwarfs the amount of antimatter that we can create in particle accelerators on Earth. (As an example, the Fermi National Accelerator Laboratory in Illinois, USA, would take an entire year, running up costs of millions of dollars, to create just one nanogram of antiprotons if the lab was used exclusively for that purpose.)

The antiprotons are produced via Earth’s interaction with incoming cosmic rays from beyond the Solar System. Cosmic rays are charged particles moving at close to the speed of light ejected from phenomena such as supernovae and their remnants. When they encounter Earth’s atmosphere they decay via pair production into antineutrons. These antineutrons can escape back into space where they decay into antiprotons and become trapped in Earth’s magnetic field. This process makes up the majority of the antimatter above Earth, but PAMELA also found that antiprotons were also being directly produced through pair production above the Earth…… Read the rest of this entry »

Written by physicsgg

August 19, 2011 at 9:16 pm

Posted in SPACE

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Antiproton Radiation Belt Discovered Around Earth

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Physicists have long suspected that antiprotons must become trapped in a belt around Earth. Now they’ve found it

The Earth is constantly bombarded by high energy particles called cosmic rays. These are generated by the Sun and by other sources further afield. (The source of the highest energy cosmic rays is still a mystery).

The particles are generally protons, electrons and helium nuclei and when they collide with nuclei in the Earth’s upper atmosphere they can produce showers of daughter particles. These showers can be so extensive that they can easily be observed from the ground.

Astronomers long ago realised that these collisions must produce antiprotons, just as they do in particle accelerators on Earth. But this raises an interesting question: what happens to the antiprotons after they are created?

The antiprotons lie sandwiched between the inner and outer Van Allen belts (in red) around the Earth

Clearly, many of these antiparticles must be annihilated when they meet particles of ordinary matter. But some astronomers always suspected that the remaining antiprotons must become trapped by the Earth’s magnetic field, forming an antiproton radiation belt.

Now astrophysicists say they’ve finally discovered this long-fabled belt of antiprotons.

In 2006, these guys launched a spacecraft called PAMELA into low Earth orbit, specifically to look for antiprotons in cosmic rays.

But, like most spacecraft in low Earth orbit, PAMELA must pass daily through the South Atlantic Anomaly, a region where the Van Allen Radiation Belts come closest to the Earth’s surface. It’s here that energetic particles tend to become trapped. So if any antiprotons are caught up in the mix, that’s where PAMELA ought to find them.

Now the PAMELA team has analysed the 850 days of data, looking only at the times when the spacecraft was in the South Atlantic Anomaly (about 1.7 per cent of this time).

Lo and behold, these guys found 28 antiprotons. That’s about three orders of magnitude more than you’d expect to find in the solar wind, proving that the particles really are trapped and stored in this belt.

Antiprotons "annihiliate" if they come into contact with normal protons

This constitutes “the most abundant source of antiprotons near the Earth”, say the PAMELA team.

The South Atlantic Anomaly is well known as a thorough nuisance. Because of the high energy particles here, the Hubble Space Telescope must be switched off when it passes through several times a day; and the International Space Station has extra shielding to protect astronauts from its effects.

The discovery of an additional belt of antiprotons won’t have much impact on the danger it represents–the number of antiprotons is tiny compared to the electrons and protons trapped there.

But it’s always interesting to have theoretical predictions confirmed. That’s good science at work.

Ref: arxiv.org/abs/1107.4882: The Discovery Of Geomagnetically Trapped Cosmic Ray Antiprotons

http://www.technologyreview.com/blog/arxiv/27058/
http://www.bbc.co.uk/news/science-environment-14405122

Written by physicsgg

August 4, 2011 at 2:47 pm