Evidence for Unfractionated Magnesium Isotopes in Genesis SOS Wafers

Oxygen isotopes measured by MegaSIMS on Genesis Concentrator samples indicate a solar wind (SW) oxygen isotope composition that is related to the ^(16)O-enriched CAI composition by a large mass dependent fractionation [I]. Isotope fractionation during acceleration of the solar wind is expected to create such a large mass fractionation, but a direct test of the presence of mass fractionation in the solar wind has not been possible with sufficient precision. Unlike O and Ne, Mg isotopes are sufficiently uniform in chondrites, terrestrial samples, and other meteoritic and planetary materials from the inner solar system [2], and so offer the best opportunity for a precise (±1‰) test of the Coulomb Drag mechanism for solar wind isotope fractionation.