A South Pole neutrino experiment has measured radio waves induced by cosmic rays—thus demonstrating that its detection method works.

Detection of high-energy neutrinos, elusive particles produced in supernovae and other astrophysical events, is opening up a new window on the Universe. One way to spot them is to search for signals of neutrino collisions with molecules in large sheets of polar ice. An international collaboration working in Antarctica has now reported the detection of ice-traversing radio waves that originate from cosmic-ray-induced particle showers [1]. Even though the radio waves were generated by cosmic rays rather than neutrinos, the result establishes a proof of principle that the technique should work for neutrinos too.

Ice-sheet-based detection of cosmic neutrinos has been reported previously from the IceCube Neutrino Observatory at the South Pole [2]. In that experiment, neutrino collisions with water molecules produce flashes of visible light, called Cherenkov radiation, generated by fast-moving collision by-products. This method becomes challenging for neutrinos of extremely high energy (around 10¹⁸ electron volts, or 1 exa-electron-volt) because these neutrinos are expected to be exceedingly rare. Researchers would need detectors spread over hundreds of cubic kilometers of ice to have a chance of seeing Cherenkov radiation from such a rare exa-electron-volt event.