Constraints on the Formation Age of Cometary Material from the NASA Stardust Mission

We measured the Al-26-Mg-26 isotope systematics of a similar to 5-micrometer refractory particle, Coki, returned from comet 81P/Wild 2 in order to relate the time scales of formation of cometary inclusions to their meteoritic counterparts. The data show no evidence of radiogenic Mg-26 and define an upper limit to the abundance of Al-26 at the time of particle formation: Al-26/Al-27 < 1 x 10(-5). The absence of Al-26 indicates that Coki formed >1.7 million years after the oldest solids in the solar system, calcium-and aluminum-rich inclusions (CAIs). The data suggest that high-temperature inner solar system material formed, was subsequently transferred to the Kuiper Belt, and was incorporated into comets several million years after CAI formation.