Hydrogen fluence in Genesis collectors: Implications for acceleration of solar wind and for solar metallicity.

NASA's Genesis mission was flown to capture samples of the solar wind and return them to the Earth for measurement. The purpose of the mission was to determine the chemical and isotopic composition of the Sun with significantly better precision than known before. Abundance data are now available for noble gases, magnesium, sodium, calcium, potassium, aluminum, chromium, iron, and other elements. Here, we report abundance data for hydrogen in four solar wind regimes collected by the Genesis mission (bulk solar wind, interstream low-energy wind, coronal hole high-energy wind, and coronal mass ejections). The mission was not designed to collect hydrogen, and in order to measure it, we had to overcome a variety of technical problems, as described herein. The relative hydrogen fluences among the four regimes should be accurate to better than ±5-6%, and the absolute fluences should be accurate to ±10%. We use the data to investigate elemental fractionations due to the first ionization potential during acceleration of the solar wind. We also use our data, combined with regime data for neon and argon, to estimate the solar neon and argon abundances, elements that cannot be measured spectroscopically in the solar photosphere.

Elemental abundances of major elements in the solar wind as measured in Genesis targets and implications on solar wind fractionation.

We present elemental abundance data of C, N, O, Na, Mg, Al, Ca, and Cr in Genesis silicon targets. For Na, Mg, Al, and Ca, data from three different SW regimes are also presented. Data were obtained by backside depth profiling using Secondary Ion Mass Spectrometry. The accuracy of these measurements exceeds those obtained by in-situ observations; therefore the Genesis data provide new insights into elemental fractionation between Sun and solar wind, including differences between solar wind regimes. We integrate previously published noble gas and hydrogen elemental abundances from Genesis targets, as well as preliminary values for K and Fe. The abundances of the solar wind elements measured display the well-known fractionation pattern that correlates with each elements' First Ionization Potential (FIP). When normalized either to spectroscopic photospheric solar abundances or to those derived from CI-chondritic meteorites, the fractionation factors of low-FIP elements (K, Na, Al, Ca, Cr, Mg, Fe) are essentially identical within uncertainties, but the data are equally consistent with an increasing fractionation with decreasing FIP. The elements with higher FIPs between ~11 and ~16 eV (C, N, O, H, Ar, Kr, Xe) display a relatively well-defined trend of increasing fractionation with decreasing FIP, if normalized to modern 3D photospheric model abundances. Among the three Genesis regimes, the Fast SW displays the least elemental fractionation for almost all elements (including the noble gases) but differences are modest: for low-FIP elements the precisely measured Fast-Slow SW variations are less than 3%.

Solar wind neon from Genesis: implications for the lunar noble gas record.

Lunar soils have been thought to contain two solar noble gas components with distinct isotopic composition. One has been identified as implanted solar wind, the other as higher-energy solar particles. The latter was puzzling because its relative amounts were much too large compared with present-day fluxes, suggesting periodic, very high solar activity in the past. Here we show that the depth-dependent isotopic composition of neon in a metallic glass exposed on NASA's Genesis mission agrees with the expected depth profile for solar wind neon with uniform isotopic composition. Our results strongly indicate that no extra high-energy component is required and that the solar neon isotope composition of lunar samples can be explained as implantation-fractionated solar wind.