Scientific American New radio-based observatories could soon detect ultrahigh-energy neutrinos, opening a new window on extreme cosmic physics Print An artist’s composite of the IceCube Neutrino Observatory in Antarctica, accompanied by a distant astrophysical source emitting neutrinos that are detected in IceCube’s subsurface sensors. Credit: IceCube and NSF Advertisement Ever since their discovery in the 1960s, ultrahigh-energy cosmic rays have captivated scientists, who wonder where they come from. Like all cosmic rays, they are arguably misnamed: they are not “rays” of radiation but rather subatomic particles, such as protons or even entire nuclei, zipping through space. Such ultrahigh energies come from ultrahigh speeds, approaching that of light itself.