¹Juulia-Gabrielle Moreau,¹Argo Jõeleht,¹Jaan Aruväli,²Mikko J. Heikkilä,³Aleksandra N. Stojic,²Thomas Thomberg,¹Jüri Plado,⁴Satu Hietala
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13782]
¹Department of Geology, Institute of Ecology and Earth Science, University of Tartu, Ravila 14A, Tartu, 50411 Estonia
²Department of Chemistry, University of Helsinki, P.O. Box 55 (A.I. Virtasen aukio 1), FI-00014 Finland
³Institut für Planetologie, Westfälische Wilhelms Universität Münster, Wilhelm-Klemm-Str. 10, Münster, 48149 Germany
⁴Geological Survey of Finland, Neulamäentie 5, Kuopio, FI-70211 Finland
Published by arrangement with John Wiley & Sons

Stoichiometric troilite (FeS) is a common phase in differentiated and undifferentiated meteorites. It is the endmember of the iron sulfide system. Troilite is important for investigating shock metamorphism in meteorites and studying spectral properties and space weathering of planetary bodies. Thus, obtaining coarse-grained meteoritic troilite in quantities is beneficial for these fields. The previous synthesis of troilite was achieved by pyrite or pyrrhotite heating treatments or chemical syntheses. However, most of these works lacked a visual characterization of the step by step process and the final product, the production of large quantities, and they were not readily advertised to planetary scientists or the meteoritical research community. Here, we illustrate a two-step heat treatment of pyrite to synthesize troilite. Pyrite powder was decomposed to pyrrhotite at 1023–1073 K for 4–6 h in Ar; the run product was then retrieved and reheated for 1 h at 1498–1598 K in N2 (gas). The minerals were analyzed with a scanning electron microscope, X-ray diffraction (XRD) at room temperature, and in situ high-temperature XRD. The primary observation of synthesis from pyrrhotite to troilite is the shift of a major diffraction peak from ~43.2°2θ to ~43.8°2θ. Troilite spectra matched an XRD analysis of natural meteoritic troilite. Slight contamination of Fe was observed during cooling to troilite, and alumina crucibles locally reacted with troilite. The habitus and size of troilite crystals allowed us to store it as large grains rather than powder; 27 g of pyrite yielded 17 g of stochiometric troilite.

¹William S.Cassata,²Kevin J.Zahnle,^1,3Kyle M.Samperton,¹Peter C.Stephenson,¹Josh Wimpenny
Earth and Planetary Science Letters 580, 117349 Link to Article [https://doi.org/10.1016/j.epsl.2021.117349]
¹Nuclear and Chemical Sciences Division, Lawrence Livermore National Laboratory, L-235, Livermore, CA 94550, USA
²Space Science Division, NASA Ames Research Center, MS 245-3, Moffett Field, CA 94035, USA
³Trace Nuclear Measurement Technology Group, Savannah River National Laboratory, Aiken, SC 29808, USA
Copyright Elsevier

Trapped, paleoatmospheric xenon (Xe) in the Martian regolith breccia NWA 11220 is mass-dependently fractionated relative to solar Xe by 16.2 ± 2.7‰/amu. These data indicate that fractionation of atmospheric Xe persisted for hundreds of millions of years after planetary formation. Such a protracted duration of atmospheric Xe mass fractionation, which is particularly striking when compared to the non-fractionated state of Martian atmospheric krypton (Kr), cannot be easily reconciled with Xe escape as a neutral atom in a neutral hydrodynamic hydrogen wind. However, Xe escape as an ion coupled to a partially ionized hydrogen or oxygen wind provides a simple solution to problems associated with the neutral escape hypothesis. Ionic Xe escape requires a sufficiently high escape flux of a carrier ion (H+ or O+) and probably requires a structured planetary magnetic field to channel the flow. The end of Xe escape from Mars could be attributed to waning hydrogen sources from volcanic outgassing or from interactions of reduced impactors with surface water and ice. Alternatively, if Xe ions were driven off by O+, the end of Xe escape could be attributed to the decay of solar extreme ultra-violet radiation.

^1,2Damien Daval,³Gaël Choblet,³Christophe Sotin,⁴François Guyot
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2021JE006995]
¹Université de Strasbourg / CNRS / ENGEES – Institut Terre et Environnement de Strasbourg, UMR, 7063 Strasbourg, France
²Université Grenoble Alpes, Université Savoie Mont Blanc, CNRS, IRD, IFSTTAR, Intitut des Sciences de la Terre, Grenoble, France
³Université de Nantes / CNRS – Laboratoire de Planétologie et Géodynamique, UMR, 6112 Nantes, France
⁴Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Museum National d’Histoire Naturelle, UMR, Sorbonne-Université / CNRS, 7590 Paris, France
Published by arrangement with John Wiley & Sons

The Cassini spacecraft demonstrated that Saturn’s small moon Enceladus may harbor hydrothermal activity. In particular, molecular hydrogen production could result from water-rock interactions in a tidally-heated, water-filled porous rocky core. The lifetime of such reactions is key to assess the habitability potential of Enceladus and to constrain plausible durations of the active stage in a context where the evolution of the moon is debated. Although it has recently been suggested that the serpentinization timescale does not exceed a few hundred million years, this estimation was based on assumptions regarding silicate dissolution kinetics that are prone to overestimate the actual reactivity of primary silicates. Here, we investigated plausible rate-limiting mechanisms governing fluid-rock interactions that could delay the completion of Enceladus’ core serpentinization. In particular, we considered the impact of (i) various secondary mineral assemblages on the Gibbs free energy of Fe-bearing silicate dissolution and associated dissolution rates; (ii) rate-laws alternative to the transition state theory; (iii) diffusion in nanoporous secondary assemblages; (iv) slow water supply. Overall, our results confirm that serpentinization timescales never exceed 500 Myr, and indicate that fluid flow ultimately sets the tempo for serpentinization. Only unreasonable grain sizes in Enceladus’ core (> 1m) or unexpectedly low diffusivity of secondary coatings covering primary silicates would be consistent with serpentinization durations of several billion years. We thus suggest that either the hydrothermal activity has developed recently on Enceladus, or alternative processes (pyrolysis of insoluble organic matter, microbial activity) must be tested to explain the observed H2 flux in Enceladus’ plume.

¹M. A. Torcivia,¹C. R. Neal
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2020JE006799]
¹University of Notre Dame
Published by arrangement with John Wiley & Sons

The ferroan anorthosite suite (FAS) represents the only direct sampling of the lunar magma ocean (LMO) and potentially contains information on the earliest history of the Moon. Apollo 16 FAS sample 60025 is extremely important for understanding early lunar evolution, but unraveling this information is complicated. For example, 60025 has two distinct Sm-Nd crystallization ages that in themselves encapsulate the complicated history of this sample, along with the cataclastic and heterogeneous textures exhibited. Here we present new in-situ major and trace element plagioclase and pyroxene data gathered from 5 thin sections of 60025 that highlight such complexities. Trace element data are used to derive equilibrium liquids and while many of the minerals analyzed here are consistent with derivation from the LMO, there are also a significant number of plagioclase and pyroxene crystals that crystallized from magmas inconsistent with current models of LMO evolution. Integration of Sm-Nd isotopic data with the elemental data reported here indicated a non-chondritic LMO is possible and we confirm that 60025 is a polymict lunar breccia containing differently sourced material.

¹Reggie L.Hudson,^1,2Yukiko Y.Yarnall
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.114899]
¹Astrochemistry Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
²Universities Space Research Association, Greenbelt, MD 20771, USA
Copyright Elsevier

Infrared (IR) spectra of two solid aromatic compounds, benzene (C6H6) and pyridine (C5H5N), have been recorded in their amorphous and crystalline states. Measurements of density and refractive index (λ = 670 nm) are reported for each form of each compound, quantities needed to compute IR intensities and optical constants for use in laboratory experiments and astronomical observations. These are the first such measurements of each compound’s density, refractive index, and spectra at temperatures relevant to the outer solar system and interstellar medium, with all measurements being made in a single laboratory. We have used these results to determine both IR band strengths and optical constants for benzene and pyridine ices in amorphous and crystalline forms. Also, the intensity of benzene’s IR absorbance near 1477 cm−1 is measured in samples containing H2O-ice and compared to the strength of the same band in anhydrous amorphous benzene, the first comparison of this type for this compound. Suggestions are made for applications and future work related to the chemistry of icy bodies in the Solar System and the interstellar medium.

¹Kareta T.,¹Reddy V.,²Pearson N.,²Sanchez J.A.,¹Harris W.M.
Planetary Science Journal 5, 190 Link to Article [DOI 10.3847/PSJ/ac1bad]
¹Lunar and Planetary Laboratory, University of Arizona, 1629 E University Boulevard, Tucson, 85721, AZ, United States
²Planetary Science Institute, 1700 East Fort Lowell, Tucson, 85719, AZ, United States

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Sanchez J.A.,²Reddy V.,³Bottke W.F.,²Battle A.,²Sharkey B.,²Kareta T.,¹Pearson N.,²Cantillo D.C.
Planetary Science Journal 5, ac235f Link to Article [DOI 10.3847/PSJ/ac235f]
¹Planetary Science Institute, 1700 East Fort Lowell Road, Tucson, 85719, AZ, United States
²Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Boulevard, Tucson, 85721-0092, AZ, United States
³Southwest Research Institute, Suite 300 1050 Walnut Street, Boulder, 80301, CO, United States

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Borlina C.S., ¹Weiss B.P.,²Bryson J.F.J.,³Bai X.-N.,¹Lima E.A.,¹Chatterjee N.,¹Mansbach E.N.
Science Advances 42, eabj6928 Link to Article [DOI 10.1126/sciadv.abj6928]
¹Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, United States
²Department of Earth Sciences, Oxford University, Oxford, United Kingdom
³Institute for Advanced Study and Department of Astronomy, Tsinghua University, Beijing, China

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

^1,2,3Tatsumi E. et al. (>10)
Nature Communications 12, 5837 Link to Articles [DOI 10.1038/s41467-021-26071-8]
¹Instituto de Astrofísica de Canarias (IAC), La Laguna, Tenerife, Spain
²Department of Astrophysics, University of La Laguna, La Laguna, Tenerife, Spain
³The University of Tokyo, Bunkyo, Tokyo, Japan

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹I.Blanchard,¹D.C.Rubie,³E.S.Jennings,³I.A.Franchi,³X.Zhao,¹S.Petitgirard,¹N.Miyajima,⁴S.A.Jacobson,⁵A.Morbidelli
Earth and Planetary Science Letters 580, 117374 Link to Article [https://doi.org/10.1016/j.epsl.2022.117374]
¹Bayerisches Geoinstitut, Universität Bayreuth, 95440 Bayreuth, Germany
²Department of Earth and Planetary Sciences, Birkbeck, University of London, Malet Street, London WC1E 7HX, UK
³School of Physical Sciences, Open University, Milton Keynes MK7 6AA, UK
⁴Department of Earth and Environmental Sciences, Michigan State University, East Lansing, MI 48824, USA
⁵Laboratoire Lagrange, Université Côte d’Azur, CNRS, Observatoire de la Côte d’Azur, 06304 Nice, France
Copyright Elsevier

Carbon is an essential element for the existence and evolution of life on Earth. Its abundance in Earth’s crust and mantle (the Bulk Silicate Earth, BSE) is surprisingly high given that carbon is strongly siderophile (metal-loving) at low pressures and temperatures, and hence should have segregated almost completely into Earth’s core during accretion. Estimates of the concentration of carbon in the BSE lie in the range 100–260 ppm and are much higher than expected based on simple models of core–mantle differentiation. Here we show through experiments at the putative conditions of Earth’s core formation (49–71 GPa and 3600–4000 K) that carbon is significantly less siderophile at these conditions than at the low pressures (≤13 GPa) and temperatures (≤2500 K) of previous large volume press studies, but at least an order of magnitude more siderophile than proposed recently based on an experimental approach that is similar to ours. Using our new data along with previously published results, we derive a new parameterization of the pressure–temperature dependence of the metal–silicate partitioning of carbon. We apply this parameterization in a model that combines planet formation and core-mantle differentiation that is based on astrophysical N-body accretion simulations. Because differentiated planetesimals were almost completely depleted in carbon due to sublimation at high temperatures, almost all carbon in the BSE was added by the accretion of fully-oxidized carbonaceous chondrite material from the outer solar system. Carbon is added to the mantle continuously throughout accretion and its concentration reaches values within the BSE range (e.g. 140+-40 ppm) at the end of accretion. The corresponding final core and bulk Earth carbon concentrations are 1270+-300 ppm and 495+-125 ppm respectively.