For decades, scientists have known that supernovae, the explosive deaths of giant stars, trigger reactions to forge most of the heavy elements in the universe. Textbook reactions cannot explain the emergence of unusual isotopes of metals such as molybdenum and ruthenium seen in the sun and meteorites. Now researchers report that antineutrinos, ghostly particles with tiny masses, might generate these rare ingredients. In the first seconds after a supernova, a region rich in protons emerges around the dead star's core, which has most likely collapsed into a neutron star. In the April 14 Physical Review Letters, investigators at the University of Basel in Switzerland and their colleagues suggest antineutrinos streaming in huge numbers from the neutron star could irradiate the protons and turn some into neutrons, which build stable, heavy isotopes. This process could assist in explaining the surprisingly large number of certain heavy elements, such as strontium, seen in otherwise metalpoor stars.