Discovered : A Belt of Antimatter Surrounding Earth

Anti-particles are not as exotic as many think and here’s further proof. The PAMELA spacecraft has detected a ring of anti-protons around the Earth, confined in that region by Earth’s magnetic field. These may be confined in that small region for hours before annihilating with matter and producing radiation.

This ground-breaking discovery was reported by PAMELA spacecraft recently. PAMELA, acronym for Payload for Anti-Matter Exploration and Light-nuclei Astrophysics, is a satellite that was launched to further cosmic ray astrophysics on 15th June 2006. It was specifically built to focus on the occurrence and interactions of positrons (anti-electrons) and anti-protons in the space around Earth.

The PAMELA spacecraft

Some theoretical considerations

Anti-matter is a theoretical necessity, which can be deduced from the symmetry of theories in physics. It was first predicted by the great Paul Dirac in 1931, following the interpretation of results given by his own equation (unsurprisingly called, the Dirac Equation) to describe the electron. His wild prediction of the positron was soon experimentally verified the following year by Carl Anderson, who detected it in his lab. (Remember, that the neutron was not yet known. It was also discovered in 1932 late in the year.) The scientific impact and importance can be gauged from the fact that Anderson went onto win the Nobel Prize in 1936, just four years after the discovery. Now, we know that every particle must have its anti-particle.

When particles and anti-particles collide, they annihilate producing (two) gamma rays. As always in physics, the reverse can also happen. Given certain conditions, a gamma ray can give rise to two particles a particle and an anti-particle obeying Einstein’s famous equation E=mc2. (Due to other strong constraints imposed by symmetries of physics, two particles or two anti-particles cannot be produced.)

The Van Allen Radiation Belts (Courtesy: Addison Wesley Longman)

In our atmosphere too, the same phenomenon happens. High energy cosmic rays bombard the Earth’s atmosphere producing matter and anti-matter particles. These can be kept separated out from each other due to the presence of Earth’s magnetic field, since moving particles of opposite charge behave very differently in magnetic fields. Furthermore, magnetic fields can confine these particles in pockets. They can remain stable for hours on average, before encountering matter particles and annihilating. Theoreticians have long predicted the presence of anti-protons in the Van Allen Belts (belts of charged particles surrounding Earth), in addition to positrons, because of the high energy of the bombarding cosmic rays. Anti-protons are much more massive than anti-electrons and thus require more energy to be produced. Most radiation can produce electron-positron pairs, but do not have enough energy to produce proton-antiproton pairs.


PAMELA collected data over 850 days from the South Atlantic anomaly (a region over the South Atlantic ocean, where the Van Allen belts come closest to the Earth’s surface) and confirmed this theoretical prediction.

As this news spreads, there will be inevitable attempts at grabbing eyeballs by projecting this as the new cheap, easily available energy source. You can lend an ear to that at your own risk.

Published by

Debjyoti Bardhan

Is a science geek, currently pursuing some sort of a degree (called a PhD) in Physics at TIFR, Mumbai. An enthusiastic but useless amateur photographer, his most favourite activity is simply lazing around. He is interested in all things interesting and scientific.