INTERSTELLAR GRAINS IN METEORITES

Primitive meteorites contain grains of silicon carbide, graphite and diamond formed outside the Solar System and probably before its birth. The isotopic compositions of these grains provide a record of stellar nucleosynthesis and of condensation processes near carbon stars; the fact of their survival places constraints on conditions in the solar nebula and early Solar System. The search is now on for other surviving stellar condensates, such as nitrides and oxides.