Diverse supernova sources of pre-solar material inferred from molybdenum isotopes in meteorites

Variations in the isotopic composition of some components in primitive meteorites demonstrate that the pre-solar material was not completely homogenized, nor was it processed at sufficiently high temperatures to erase the signatures of the diverse stellar sources(1). This is in accord with the observation that accretion disks of young stellar objects are at relatively low temperatures(2). Carbonaceous chondrites are considered to represent the 'average' Solar System composition; the rare pre-solar grains in the matrixes of carbonaceous chondrites(3) have been used to identify some sources of the pre-solar material. Here we report that the molybdenum isotopic composition of bulk carbonaceous chondrites is distinctly different from the accepted average solar value. We show that the Mo data require the presence of material produced in at least two different r-processes, and that the contribution from the p-process material is decoupled from the r-process, all occurring in supernova explosions. This is consistent with the emerging picture of diverse sources inferred from short-lived isotopes in the early Solar System(4) and elemental analyses of metal-poor stars(5,6).