Presolar grain

A microscopic solid particle that formed around an older star before the Solar System and survived inside primitive meteorites. Its unusual isotopic composition records the stellar environment where it formed.

Isotope: An atom of a chemical element with a particular number of neutrons in its nucleus. Presolar grains are identified chiefly by isotope ratios unlike those in Solar System materials.
Asymptotic giant branch star: A cool, luminous late-stage star with a carbon–oxygen core and alternating shell burning. Many silicon carbide grains condensed in the outflows of these evolved stars.
Dust condensation: The formation of solid particles from atoms and molecules in a gas. Stellar outflows cooled enough for elements to condense into presolar solids.
Stellar nucleosynthesis: The production of elements and isotopes by nuclear reactions inside stars. Grain isotope ratios provide direct samples of stellar nucleosynthesis products.
Isotopic anomaly: A measurable departure in isotope ratios from a reference composition. Anomalous isotope ratios distinguish presolar grains from material formed in the Solar System.
Red giant: A luminous, expanded star nearing or undergoing late stages of stellar evolution. Some oxide grains record material processed and expelled during red-giant evolution.
Silicon carbide: A hard compound of silicon and carbon found naturally in some meteorites. It is a well-studied presolar mineral with distinctive stellar isotope signatures.
Oxygen isotope ratio: A comparison of the abundances of oxygen’s stable isotopes in a material. Its variation among oxide grains helps classify their parent stars.
Primitive meteorite: A meteorite that retains relatively unaltered material from the early Solar System. These meteorites preserve grains that escaped extensive melting and chemical processing.
Core-collapse supernova: The explosive death of a massive star after its core collapses. A small fraction of presolar grains carry isotope patterns attributed to supernova ejecta.

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