Local and exotic components of primitive meteorites, and their origin

Most of the material of chondrites was heavily reprocessed in the early Solar System, and hence retains only a dim memory of its interstellar origin even in the least altered meteorites. Opaque matrix, the most primitive material, seems to have taken up Fe2+ and changed its mineralogy and texture. Chondrules and Ca, Al-rich inclusions have been further altered by melting, oxidation or reduction, loss of volatiles, etc. None the less, small amounts of exotic components have survived, as indicated by isotopic anomalies. A dust component enriched in ieO is the most abundant and widespread. It survives in Ca, Al-rich inclusions as anomalous spinel grains, but is recognizable even in highly evolved meteorites and planets from variations in bulk oxygen isotopic composition. A few inclusions show small nucleosynthetic anomalies for many elements (Si, Ca, Ti, Cr, Sr, Ba, Nd, Sm), always coupled with mass fractionation of several of these elements, as well as 0 and Mg. Seven extinct radionuclides ( 26 AI, 41 Ca, 53 Mn, 107 Pd, 129 I, 146 Sm, and 244 Pu) have been recognized from their decay products, and provide clues to the chronology and nucleosynthetic sources of the early Solar System. Highly volatile elements, such as C, N and the noble gases, show especially large and numerous isotopic anomalies. The noble-gas components include Ne-E (monoisotopic 22 Ne from the (B+ decay of 2.6a 22 Na), Xe-HL (enriched 2-fold in the light and heavy isotopes), and Xe-S (enriched in the even-numbered, middle isotopes 128, 130 and 132). They are located in carriers that themselves are anomalous, e.g. carbon enriched up to 2.4-fold in 13 C or depleted by more than 30 % in 15 N, or spinel enriched in 16 O and 13 C. Other anomalies include nitrogen enriched 2-fold in 15 N and hydrogen enriched 5-fold in D ; probably relict interstellar molecules. A variety of astronomical sources seem to be required: novae, red giants, supernovae and molecular clouds.