Isotopic compositions of cometary matter returned by the STARDUST mission

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6008 Composition (1060), 6015 Dust, 6040 Origin And Evolution, 6210 Comets (6023)

Scientific paper

The STARDUST spacecraft flew through the coma of comet 81P/Wild2 on Jan. 2, 2004, at a distance of ~236km and a relative velocity of ~6.1 km/s [1]. Dust particles, which were released from the comet hours before the encounter, were captured in silica aerogel and successfully returned to the Earth on Jan. 15, 2006. Cometary debris was also retained in small impact craters on Al-foil strips adjacent to the aerogel collector cells. A prelimary examination team (PET) of ~150 scientists has been engaged in studying the mineralogy/petrology, chemistry, optical properties, organic materials, fluence, and isotopic compositions of a subset of the returned cometary materials [2,3]. This report summarizes the findings of the PET isotope subgroup during its 6 month investigation. Isotopic compositions of hydrogen, carbon, nitrogen, and oxygen show a range of heterogeneity among individual particle fragments demonstrating that the comet consists of unequilibrated samples from a variety of astrophysical environments. With one exception, extreme isotopic anomalies indicative of presolar materials are not found, indicating that the comet does not consist of an unalterered agglomeration of presolar materials. However, some organic materials were collected that show isotopic signatures consistent with molecular cloud chemistry. Neon and nitrogen isotopic compositions suggest that some volatile materials were successfully collected and trapped in the aeorgel. Oxygen isotopic evidence points toward a solar system origin for almost all crystalline silicate and oxide minerals and implies large-scale radial transport of dust formed in hot inner regions of the solar nebula outward to the Kuiper belt where Wild2 and other Jupiter family comets finally accreted. References: [1] Brownlee, D.E., et al (2004). Science 304, 1764-1769. [2] Brownlee D. E. et al. 2006. Abstract #2286. 37th Lunar & Planetary Science Conference. [3] Tsou P. et al. 2006. Abstract #2189. 37th Lunar & Planetary Science Conference.

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