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Abstract

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 supernovae1. 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 analyses2, 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 26Mg from 26Al 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 (<150 nm). Here we show that a minor but important fraction of silicate stardust believed to come from red giant stars has a supernova origin instead, if hydrogen ingestion occurred during the pre-supernova phase, making the supernova dust fraction among >200-nm-sized presolar silicates significantly higher than previously inferred.