A large proportion of the matter in our universe cannot be detected by conventional means. It is called dark matter because it does not reflect any light, but we can detect its presence due to gravitational influence. Dark matter is actually much more prevalent than conventional matter, and over the years several theories have been proposed about what it actually is. We already saw that astronomers are closing in on the identity of dark matter, but it has not officially been detected yet. Measurements on board of the International Space Station have revealed traces of something that could help us find dark matter.
On board of the ISS there are several instruments that measure all kinds of parameters. One of these machines is the Alpha Magnetic Spectrometer, which can detect particles in so-called cosmic rays, which are basically showers of particles that travel through space. It detects a lot of electrons, but sometimes also encounters its positively charged counterpart: a positron. This is a form of antimatter, as it has the exact opposite characteristics when compared to an electron.
In the 18 months that the AMS has been performing measurements, it encountered approximately 400.000 positrons, the largest number of antimatter particles found so far. According to the scientists that analyzed the data, these findings could possibly provide the 'smoking gun' that is required to find traces of dark matter. Because we cannot detect dark matter directly, indirect methods are required to proof its existence and to find out what it is made of.
The scientists think that with additional data, the AMS findings may help reconstruct how dark matter particles and antiparticles annihilate each other in space, just like an electron and a positron would do when they meet. Although more methods are explored to find the illusive dark matter, the ISS may play an important role in its eventual discovery.