Bits of antimatter stream through space like a steady drizzle. They may come from the spinning stellar corpses known as pulsars. Or they could come from collisions of particles of dark matter.

The drizzle was measured by AMS, an instrument aboard the International Space Station. It's a giant magnet that directs incoming particles into a set of detectors.

AMS has three main goals. One is to study cosmic rays, which are shot into space by exploding stars and other powerful objects. A second is to search for evidence that antimatter was created in the Big Bang by looking for anti-helium — a search that so far has come up empty. And a third is to look for dark matter.

Dark matter produces no detectable energy, but reveals its presence by exerting a gravitational tug on the visible matter around it. There is much more dark matter than normal matter. It likely consists of some type of subatomic particle, but there are several ideas for what type of particle.

One is called the neutralino. If these particles collide, they should annihilate each other, producing positrons — the antimatter version of electrons.

Earlier space missions had already detected positrons. But AMS has measured them with a higher level of precision, and in far greater numbers. One possible source is pulsars. But another is dark matter. Continued observations should help scientists pick between the two choices — perhaps solving the mystery of dark matter.

Script by Damond Benningfield, Copyright 2013