Q-gases in a late-forming refractory interplanetary dust particle: A link to comet Wild 2.

We report the structure, chemical composition, O, Al-Mg, He, and Ne isotope systematics of an interplanetary dust particle, "Manchanito". These analyses indicate that Manchanito solidified as refractory glass (with oxidized Fe but reduced Ti) in a chondrule-like formation environment more than 3.2 Myr after CAIs, after which it was exposed to Q-like noble gases in the dissipating solar nebula. Manchanito's He and Ne isotopic composition and concentrations are similar to those measured in samples of comet Wild 2, from which we infer that Manchanito's parent body was a comet. We propose that after formation and exposure to Q-like gases, Manchanito was transported to the outer Solar System where it came into contact with organics and volatile ices on its cometary parent body. Manchanito provides additional evidence that cometary solids have been subjected to energetic processing and large-scale transport in a wide range of environments in the Solar System.

Helium and neon abundances and compositions in cometary matter.

Materials trapped and preserved in comets date from the earliest history of the solar system. Particles captured by the Stardust spacecraft from comet 81P/Wild 2 are indisputable cometary matter available for laboratory study. Here we report measurements of noble gases in Stardust material. Neon isotope ratios are within the range observed in "phase Q," a ubiquitous, primitive organic carrier of noble gases in meteorites. Helium displays 3He/4He ratios twice those in phase Q and in Jupiter's atmosphere. Abundances per gram are surprisingly large, suggesting implantation by ion irradiation. The gases are probably carried in high-temperature igneous grains similar to particles found in other Stardust studies. Collectively, the evidence points to gas acquisition in a hot, high ion-flux nebular environment close to the young Sun.