If we can’t detect dark matter itself, however, we might detect its byproducts. Theorists think that when two dark matter particles meet out in space, they’ll occasionally, albeit not often, destroy each other in a tiny burst of energy. That energy would then condense back into entirely different particles: an ordinary electron and its much rarer antimatter counterpart, a positron, which would go speeding away from each other in some random direction.

It’s these positrons that AMS detected — some 400,000 of them in the nearly two years it’s been in operation. The number and energy of the positrons is consistent with what theorists would expect if dark matter really is smashing into itself throughout the Milky Way. So is the fact that the positrons are hitting the detector from all directions, which it should if dark matter truly pervades the Milky Way. Says, Jeremiah Ostriker, a Princeton astrophysicist who has been in the forefront of dark-matter theory since the 1970’s, “the AMS experiment may — just may — have detected [evidence of] dark matter decay.”