INCORPORATION OF A LATE-FORMING CHONDRULE INTO COMET WILD 2

Abstract

We report the petrology, O isotopic composition, and Al-Mg isotope\nsystematics of a chondrule fragment from the Jupiter-family comet Wild 2,\nreturned to Earth by NASA's Stardust mission. This object shows characteristics\nof a type II chondrule that formed from an evolved oxygen isotopic reservoir.\nNo evidence for extinct 26Al was found, with (26Al/ 27Al)0 < 3.0 x 10^-6.\nAssuming homogenous distribution of 26Al in the solar nebula, this particle\ncrystallized at least 3 Myr after the earliest solar system objects--relatively\nlate compared to most chondrules in meteorites. We interpret the presence of\nthis object in a Kuiper Belt body as evidence of late, large-scale transport of\nsmall objects between the inner and outer solar nebula. Our observations\nconstrain the formation of Jupiter (a barrier to outward transport if it formed\nfurther from the Sun than this cometary chondrule) to be more than 3 Myr after\ncalcium-aluminum-rich inclusionss.\n