title: Constraints on the formation age of cometary material from the NASA Stardust mission.
abstract: We measured the 26Al-26Mg isotope systematics of a approximately 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 26Mg and define an upper limit to the abundance of 26Al at the time of particle formation: 26Al/27Al < 1 x 10(-5). The absence of 26Al 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.
authors.affiliation: Institute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA. matzel2@llnl.gov
authors.forename: J E P
authors.initials: JE
authors.lastname: Matzel
authors.forename: H A
authors.initials: HA
authors.lastname: Ishii
authors.forename: D
authors.initials: D
authors.lastname: Joswiak
authors.forename: I D
authors.initials: ID
authors.lastname: Hutcheon
authors.forename: J P
authors.initials: JP
authors.lastname: Bradley
authors.forename: D
authors.initials: D
authors.lastname: Brownlee
authors.forename: P K
authors.initials: PK
authors.lastname: Weber
authors.forename: N
authors.initials: N
authors.lastname: Teslich
authors.forename: G
authors.initials: G
authors.lastname: Matrajt
authors.forename: K D
authors.initials: KD
authors.lastname: McKeegan
authors.forename: G J
authors.initials: GJ
authors.lastname: MacPherson