A Comparison of Solar Wtnd and Estimated Solar System Xenon Abundances : A Test for Solid / Gas Fractionation in the Solar Nebula

Significant fractionation of dust/gas from the original interstellar doud during the formation of the solar system is a distinct posfilbility. Identification of such an effect would provide important clues to nebular processes. Fractionation of volatiles is not constrained by CI abundances and only for the most abundant ones by photospheric observations. The solar Xe elemental abundance is determined here via solar wind measurements from lunar ilmenites and nonnalized to Si by spacecraft data. The results are compared with estimated abundances assuming no fractionation, which are relatively well constrained for Xe by s-process calculations, odd-mas.5 abundance interpolations, and odd-even abundance systematics. When corrected for solar wind/photospheric fractionation, the 130xe abundance given by surface layer oxidation of ilmenite from soil 71501, exposed within the last 200 m.y., is 0.24 ± 0.09 nonnalized to Si = 106. This is indistinguishable from the estimates made assuming no solid/gas fractionation. A similar result was obtained for Kr by Wiens et al ( 1991 ). Results from breccia 79035 ilmenite, exposed at least 1 Gy ago, indicate that the solar wind Xe flux may have been significantly higher relative to other noble gases, perhaps due to more efficient Xe ionization. If this is true, fl.uxes of C and S, which have similar first ionization potentials to Xe, should also be higher in the ancient solar wind from the same time period, though such variations have not been observed 153