A new population of dust from stellar explosions among meteoritic stardust

Primitive Solar System materials host small amounts of refractory dust grains predating the formation of the Sun and its planetary system. These ‘presolar’ grains condensed in the ejecta of evolved stars, novae and supernovae 1 . Their highly anomalous isotopic compositions cannot be explained by chemical or physical processes within the Solar System; instead, they represent the nucleosynthetic signatures of their stellar parents. Among this ‘true stardust’, silicates are the most abundant type of dust available for single-grain analyses 2 , with typical sizes of approximately 150 nm (ref. 3 ). Unlike presolar silicon carbides, aluminium oxides or graphites, which can be separated chemically from meteorites, presolar silicates have to be identified in situ, as they would be destroyed by extraction agents. Instrumental restrictions have constrained almost all previous magnesium isotopic measurements to presolar aluminium oxides, and the contribution of radiogenic 26 Mg from 26 Al decay has precluded unambiguous conclusions about their initial magnesium isotopes. Recent technical advances have enabled the undisturbed in situ investigation of magnesium isotopes in presolar silicates with unprecedented spatial resolution (200-nm-sized presolar silicates significantly higher than previously inferred 1 . A minor but important fraction of silicate stardust believed to come from red giant stars is shown to have a supernova origin instead, making the supernova dust fraction among >200-nm-sized presolar silicates significantly higher than previously inferred.