Western-Hemisphere Neutrino Detector Captures First Geoneutrinos, Hinting at Mantle Variations

Deep beneath Sudbury, Canada, the SNO+ neutrino observatory has recorded its inaugural geoneutrinos, increasing the worldwide tally by roughly 50 and marking the first such observations from the western hemisphere. The detector, a 780-ton scintillator sphere shielded by water and rock, captures fleeting light flashes when neutrinos interact with the liquid. Geoneutrinos arise from the decay of heat-producing elements—uranium, thorium and potassium—within Earth's mantle and crust, offering a direct probe of internal heat that drives plate tectonics and the magnetic field.

Compared with earlier measurements at Japan's Kamland and Italy's Borexino, SNO+ reports an intermediate flux, hinting that mantle composition may vary regionally, perhaps linked to large low-shear-velocity provinces beneath Africa and the Pacific. Nonetheless, scientists stress large uncertainties from background subtraction, crustal contributions, and detector calibration, and await additional data from the upcoming JUNO experiment in China and potential ocean-bottom detectors to refine the picture.