Showing papers by "Gary R. Huss published in 2020"

Magnesium Isotopes of the Bulk Solar Wind from Genesis Diamond-Like Carbon Films

Abstract: NASA's 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 ≤1‰) 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‰, -30.2‰) ± (4.1‰, 5.5‰), where the uncertainty is 2ơ SE of the data combined with a 2.5‰ (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).

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

Abstract: 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.

Volatile abundances and hydrogen isotope ratios of apatite in Martian basaltic breccia NWA 11522—A paired stone of NWA 7034

Abstract: This study aimed to determine the volatile content (Cl, F, OH) and hydrogen isotope (D/H) ratios of apatite grains within the Martian meteorite NWA 11522, a paired stone of the ungrouped polymict breccia NWA 7034. Apatite F:Cl:OH ratios were measured via SEM‐EDS analyses, and found to be strikingly similar in all grains, and dominated by Cl. Apatite D/H ratios were measured in situ via the Cameca ims 1280 SIMS at the University of Hawai'i. Results varied between δD values of 782 and 52 ‰ and between water contents of 0.127 and 0.510 wt%. The data form a mixing line between two endmembers. The first endmember, a high D/H ratio and low water content endmember, represents a fluid present during the thermal event that lithified the breccia at 1.5 Ga, resetting apatite volatile content, D/H ratio, and U‐Pb ages at this time. The D/H ratio of this fluid suggests that it was derived from the crust/cryosphere (e.g., melted groundwater ice). The second endmember, a low D/H ratio and high water content endmember, represents a second Martian fluid that interacted with the breccia after lithification. The low D/H ratio of this later fluid indicates it was derived from the deeper Martian interior, and may be evidence of an impact‐related hydrothermal system on Mars during the Amazonian period. The presence of these fluids within NWA 11522 suggests that subsurface impact crater environments were still host to liquid water during the past 1.5 Ga on Mars, and still could be to this day.

Oxygen isotopic composition of an enstatite ribbon of probable cometary origin.

Abstract: Filamentary enstatite crystals are found in interplanetary dust particles (IDPs) of likely cometary origin but are very rare or absent in meteorites. Crystallographic characteristics of filamentary enstatites indicate that they condensed directly from vapor. We measured the O isotopic composition of an enstatite ribbon from a giant cluster IDP to be δ18O = 25 ± 55, δ17O = -19 ± 129, Δ17O = -32 ± 134 (2σ errors), which is inconsistent at the 2σ level with the composition of the Sun inferred from the Genesis solar wind measurements. The particle's O isotopic composition, consistent with the terrestrial composition, implies that it condensed from a gas of nonsolar O isotopic composition, possibly as a result of vaporization of disk region enriched in 16O-depleted solids. The relative scarcity of filamentary enstatite in asteroids compared to comets implies either that this crystal condensed from dust vaporized in situ in the outer solar system where comets formed or it condensed in the inner solar system and was subsequently transported outward to the comet-forming region.