Presolar grains

Presolar grains are any solid material formed before the coalescence of the Sun, the star at the center of the Solar System. This material is most frequently encountered as tiny grains incorporated whole into asteroids and comets. Presolar grains formed within the outflow of cooling gases from stars that predate the Sun, i.e., stars that came into being earlier than 4.6 billion years ago.

The stellar nucleosynthesis that took place within these stars lent distinct isotopic signatures to presolar grains, aiding their identification. These isotopic signatures often permit the identification of specific astrophysical nuclear processes different from any that have ever occurred in the Sun, proving the presolar origin of any grains bearing these isotopic ratios.

The study of presolar grains is the domain of cosmochemistry and meteoritics.

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