Magnesium Isotopes of the Bulk Solar Wind from Genesis Diamond-Like Carbon Films
Journal Article - Open Access
NAVAL RESEARCH LAB WASHINGTON DC WASHINGTON United States
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NASAs Genesis Mission returned solar wind SW to the Earth for analysis to derive the composition of the solar photosphere from solar material. SW analyses control the precision of the derived solar compositions, but their ultimate accuracy is limited by the theoretical or empirical models of fractionation due to SW formation. Mg isotopes are ground truth for these models since, except for CAIs, planetary materials have a uniform Mg isotopic composition within or 1 parts per thousand so any significant isotopic fractionation of SW Mg is primarily that of SW formation and subsequent acceleration through the corona. This study analyzed Mg isotopes in a bulk SW diamond-like carbon DLC film on silicon collector returned by the Genesis Mission. A novel data reduction technique was required to account for variable ion yield and instrumental mass fractionation IMF in the DLC. The resulting SW Mg fractionation relative to the DSM-3 laboratory standard was -14.4 parts per thousand, -30.2 parts per thousand - 4.1 parts per thousand, 5.5 parts per thousand, where the uncertainty is 2 SE of the data combined with a 2.5 parts per thousand total error in the IMF determination. Two of the SW fractionation models considered generally agreed with our data. Their possible ramifications are discussed for O isotopes based on the CAI nebular composition of McKeegan et al. 2011.