"New results from NASA's Fermi Gamma-Ray Space Telescope appear to confirm a larger-than-expected rate of high-energy positrons reaching the Earth from outer space. This anomaly in the cosmic-ray flux was first observed by the Italian-led PAMELA spacecraft in 2008 and suggests the existence of annihilating dark-matter particles. Physicists believe that about 80% of the mass in the universe is in the form of a mysterious substance known as dark matter. ... researchers are attempting to find direct evidence of it on Earth using either heavily shielded underground detectors or with particle accelerators. But they also have a third, less direct, option – using satellites or balloon-based instruments to detect the particles that some theories predict are created in space when two dark-matter particles collide and annihilate."