Molybdenum nucleosynthetic dichotomy revealed in primitive meteorites

The collapse of the presolar cloud gave rise to a global homogenization of material available to form the Sun and planets. In the resulting, presumably homogeneous solar system, the nuclides are present in proportions referred to as their cosmic abundances. Here we report molybdenum isotopic compositions of bulk samples and leachate fractions of the primitive meteorites Orgueil and Allende. Two complementary nucleosynthetic components are revealed in Orgueil. One (Mo-m) is enriched in s-process nuclides and may be hosted in presolar grains while the other (Mo-w) is probably distributed in various phases and is depleted in s-process nuclides. The most likely carrier of Mo-m is silicon carbide, although we cannot exclude graphite or an unidentified presolar phase. Excesses in Mo-w are also detected in the bulk sample and all leachate fractions of Allende. These results illustrate that the apparent cosmic abundance pattern of the nuclides, in fact, reflects a mixture of various nucleosynthetic components that survived planetary-scale homogenization in the protosolar nebula.