A Moment of Science

Engage Antimatter Engines!

A satellite has discovered a significant source of antimatter - the Earth's Van Allen belts. This material could literally fuel space exploration!

Artist

Photo: NASA Goddard Photo and Video (Flickr)

Artist's conception of the Earth's magnetosphere and the release of magnetic energy.

Engage antimatter engines! A discovery by the PAMELA satellite could turn science fiction into reality. The satellite has discovered larger-than-expected numbers of antiprotons in Earth’s Van Allen Belts (belts of charged particles trapped by the Earth’s magnetic field).

What Is Antimatter?

The word antimatter has long been a staple term of science fiction writers to refer to a futuristic energy source. In the long-running Star Trek franchise, matter-antimatter reactions were used to power starships. We don’t have antimatter engines yet, but now reality might be one step closer to science fiction.

The first type of antimatter discovered was the positron, it was discovered in 1932 by physicist Carl David Anderson. This is not the only type of antimatter though, there are as many types of antimatter as there are subatomic particles. This is because all types of antimatter are simply subatomic particles that have the opposite electrical charge and magnetic moment of ordinary subatomic particles.

What the PAMELA satellite has discovered are antiprotrons – protons with a negative charge. Antiprotons were predicted in the 1930s, and conclusively discovered in 1955 .

Where Can We Find Antiprotons?

Antiprotons can be created in labs using a particle accelerator. But it is very difficult to store antiprotons in significant quantities on Earth. This is because when an antiproton encounters its regular matter counterpart the two particles annihilate one another and produce energy in the form of gamma rays. There is much more regular matter in our universe than antimatter so antimatter is destroyed almost immediately after it is formed – at least on Earth.

Antimatter can also be produced naturally by cosmic rays. When cosmic rays encounter neutrons that have escaped from Earth’s atmosphere, antiprotons are the result. But antiprotons formed in space will still get annihilated by any protons they encounter, so how do these antiparitcles exist long enough to accumulate?

The Van Allen Belts are a sweet spot, of sorts, for antimatter. The Van Allen Belts are regions around the earth where particles are trapped by the Earth’s magnetic field. So the antiprotons are prevented from scattering into outer space, but why aren’t the antiprotons annihilated by protons in the Van Allen Belts?

Well, antiprotons and protons will still destroy each other in the Van Allen Belts, but because the belts are outside the Earth’s atmosphere, the density of regular matter is low enough to allow antimatter to exist for a longer period of time. This combination of magnetic attraction and low regular matter density allows antiprotons to not only exist for a significant period of time but even to accumulate.

How Can We Use Antiprotons?

Remember how gamma rays are created when a proton and an antiproton collide? Gamma rays are very energetic, more energetic than any other kind of electromagnetic radiation. NASA’s Institute for Advanced Concepts has proposed that controlling proton-antiproton collisions would provide the necessary energy to power advanced spacecraft.  Even better,  such a spacecraft could refuel on naturally formed antiprotons encountered on its travels. Now that is renewable energy!

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Erin Sweany

Erin is a graduate student at Indiana University studying early English medical texts. Erin has studied both science and literature throughout her academic career. She loves science for what it tells us about our world and literature for what it tells us about our culture. Erin combines these interests in her scholarship and writing as much as possible.

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