presolar

Presolar materials are stardust particles that formed before the Sun and were later incorporated into the solar system. They are found in primitive meteorites, interplanetary dust particles, and some cometary materials. Their defining feature is isotopic compositions that differ markedly from those of the solar system, indicating origins in other stars or stellar explosions.

These grains condensed in stellar outflows and supernova ejecta, and they survived the incorporation into the solar nebula about 4.6 billion years ago. Their isotopic signatures preserve records of stellar nucleosynthesis and galactic chemical evolution, including s-process and r-process contributions, links to asymptotic giant branch stars, red giants, novae, and supernovae.

The main types of presolar grains include silicon carbide (SiC), graphite, diamonds, oxides (such as corundum and spinel), and presolar silicates. SiC grains are subdivided into mainstream grains associated with AGB stars and rare X grains linked to supernovae. Oxide grains and silicates carry oxygen isotope ratios that diagnose their stellar origins, while carbon and nitrogen isotopic ratios in various grains further distinguish their sources.

Analytical techniques such as secondary ion mass spectrometry, NanoSIMS, and resonance ionization mass spectrometry are used to measure isotopic compositions in individual grains. The study of presolar grains provides empirical constraints on models of stellar nucleosynthesis, the lifecycle of matter in the galaxy, and the inventory of solid material present in the early Solar System.