Mg Isotopic Composition of the Solar Wind by SIMS Analysis of Genesis Targets

In order to deduce the isotopic compositions in the solar nebula of volatile elements, e.g., noble gases, O, and N, from analyses of the solar wind (SW), we must understand the magnitude of mass-dependent fractionation between the SW and the photosphere. With the exception of evaporation effects in CAIs, mass-dependent fractionation of Mg isotopes is small, as evidenced by Mg isotopic compositions of terrestrial igneous and meteoritic samples which agree within ~1‰ [1]. Thus, if we assume that the "terrestrial" Mg isotopic composition is also representative of the solar photosphere, we can use measurements of the SW captured by Genesis to test models of isotopic fractionation in formation of SW. For example, if the inefficient Coulomb-drag model [2] is correct, we would expect that the Mg isotopic composition in the SW is ~10‰ per amu [2] lighter than the terrestrial composition.