Earth and neutrino detection event, illustration. The interaction of a neutrino with the oxygen atom (red) in a water ice molecule (right) has produced a secondary particle, a muon, that is moving at relativistic speed, leaving a trace of blue Cherenkov radiation (flash shown here). The IceCube Neutrino Observatory (completed 2010) is an international high-energy neutrino observatory in the ice below the Amundsen-Scott South Pole Station (lower left). Neutrinos are elementary particles that are very difficult to detect and study. The IceCube modules detect the Cherenkov radiation produced when neutrinos interact with ice. For this illustration without labels, see image C047/7666.