^1,2Megan Bedell et al. (>10)
The Astrophysical Journal 865, 68 Link to Article [https://doi.org/10.3847/1538-4357/aad908]
¹Center for Computational Astrophysics, Flatiron Institute, 162 5th Avenue, New York, NY 10010, USA
²Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Avenue, Chicago, IL 60637, USA

The compositions of stars are a critical diagnostic tool for many topics in astronomy such as the evolution of our Galaxy, the formation of planets, and the uniqueness of the Sun. Previous spectroscopic measurements indicate a large intrinsic variation in the elemental abundance patterns of stars with similar overall metal content. However, systematic errors arising from inaccuracies in stellar models are known to be a limiting factor in such studies, and thus it is uncertain to what extent the observed diversity of stellar abundance patterns is real. Here we report the abundances of 30 elements with precisions of 2% for 79 Sun-like stars within 100 pc. Systematic errors are minimized in this study by focusing on solar twin stars and performing a line-by-line differential analysis using high-resolution, high-signal-to-noise spectra. We resolve [X/Fe] abundance trends in galactic chemical evolution at precisions of 10−3 dex Gyr−1 and reveal that stars with similar ages and metallicities have nearly identical abundance patterns. Contrary to previous results, we find that the ratios of carbon-to-oxygen and magnesium-to-silicon in solar-metallicity stars are homogeneous to within 10% throughout the solar neighborhood, implying that exoplanets may exhibit much less compositional diversity than previously thought. Finally, we demonstrate that the Sun has a subtle deficiency in refractory material relative to >80% of solar twins (at 2σ confidence), suggesting a possible signpost for planetary systems like our own.

¹Alexey Potapov, ¹Cornelia Jäger, ²Thomas Henning
The Astrophysical Journal 865, 58 Link to Article [https://doi.org/10.3847/1538-4357/aad803]
¹Laboratory Astrophysics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena, Institute of Solid State Physics, Helmholtzweg 3, D-07743 Jena, Germany
²Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany

Understanding the history and evolution of small bodies, such as dust grains and comets, in planet-forming disks is very important to reveal the architectural laws responsible for the creation of planetary systems. These small bodies in cold regions of the disks are typically considered to be mixtures of dust particles with molecular ices, where ices cover the surface of a dust core or are actually physically mixed with dust. While the first case, ice-on-dust, has been intensively studied in the laboratory in recent decades, the second case, ice-mixed-with-dust, presents uncharted territory. This work is the first laboratory study of the temperature-programmed desorption of water ice mixed with amorphous carbon and silicate grains. We show that the kinetics of desorption of H2O ice depends strongly on the dust/ice mass ratio, probably due to the desorption of water molecules from a large surface of fractal clusters composed of carbon or silicate grains. In addition, it is shown that water ice molecules are differently bound to silicate grains in contrast to carbon. The results provide a link between the structure and morphology of small cosmic bodies and the kinetics of desorption of water ice included in them.

¹Frans J. M. Rietmeijer
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13201]
¹Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA
Published by arrangement with John Wiley & Sons

So far there is no conclusive evidence for water in the nucleus of 81P/comet Wild 2. Recently magnetite in collected Wild 2 samples was cited as proxy evidence for parent body aqueous alteration in this comet (Hicks et al. 2017). A potentional source for water of hydration would be layer silicates but unfortunately there is no record, neither texturally nor chemically, for hydrated layer silicates that survived hypervelocity impact in the Wild 2 samples. This paper reports large vesicles in the matrix of allocation C2044,2,41,2,5 from a volatile‐rich type B/C Stardust track. These vesicles were probably caused by boiling water that were generated when hydrated Wild 2 silicates impacted the near‐surface silica aerogel layer. Potential water sources were partially and fully hydrated GEMS (glass with embedded metal and sulfides) and CI carbonaceous chondrite materials among the earliest dusts that experienced hydration and icy‐body formation and long‐range transport and mixing with materials from across the solar system.

¹Melissa K.Ward, ¹Wayne H.Pollard
Earth and Planetray Science Letters 504, 126-138 Link to Article [https://doi.org/10.1016/j.epsl.2018.10.001]
¹Department of Geography, McGill University, Montreal, Canada
Copyright Elsevier

On Axel Heiberg Island in the Canadian High Arctic, low temperature perennial saline springs occur despite thick permafrost and cold polar desert conditions marked by a mean annual air temperature close to −20 °C. We present the first comprehensive geomorphic study of the Stolz Diapir Spring (79°04′30″N; 87°04′30″W), a unique groundwater system due to its known fresh water source and sodium chloride-dominated chemistry. During winter, spring discharge precipitates hydrohalite (NaCl⋅2H2O) by freezing fractionation that forms a pool and barrage system morphologically similar to carbonate travertines and tufas found in temperate climates. The deposit is the largest hydrohalite accumulation on Earth based on published sources. This system experiences dramatic seasonal differences in hydrology and mineralogy marked by a switch from winter regime of salt deposition and cascading surface flow from pool to pool to a summer regime marked by chemical and mechanical erosion and deposit subsurface flow. The warmer temperatures also cause the decomposition of hydrohalite to halite. Accordingly, this site is a useful analogue for similar structures identified on Mars located in areas rich in evaporite minerals and lacking evidence of volcanic activity.