: Last year the team that runs the IceCube detector at the South Pole reported the discovery of two neutrinos, nicknamed Bert and Ernie, of cosmic origin and petaelectronvolt energies (1 PeV = 1015
eV). Now the team has found a third PeV neutrino, bringing the total haul of cosmic neutrinos of all energies to 37. IceCube consists of strings of photomultiplier tubes that detect the neutrinos' extremely rare interactions with water molecules. The entire experiment occupies a volume of 1 cubic kilometer. Although the neutrinos' origins and production mechanisms remain mysterious, the directions from which they arrived at the South Pole suggest they are extragalactic.