¹Żbik, M.S.
Advances in Space research (in Press) Link to Article [DOI: 10.1016/j.asr.2020.04.017]
¹Faculty of Geology, University of Warsaw, ul. Żwirki i Wigury 93, Warsaw, 02-089, Poland

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^1,2Sharygin, V.V.
Minerals, 10, 437 Link to Article [DOI: 10.3390/min10050437]
¹V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 Acad. Koptyuga pr., Novosibirsk, 630090, Russian Federation
²ExtraTerra Consortium, Institute of Physics and Technology, Ural Federal University, 19 Mira str., Ekaterinburg, 620002, Russian Federation

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^1,2Alfio Alessandro Chiarenza,³Alexander Farnsworth,²Philip D. Mannion,³Daniel J. Lunt,³Paul J. Valdes,¹Joanna V. Morgan,¹Peter A. Allison
Proceedings of the National Academy of Sciences of the United States of America 117, 17084-17093 Link to Article [DOI: https://doi.org/10.1073/pnas.2006087117]
¹Department of Earth Science and Engineering, Imperial College London, South Kensington, SW7 2AZ London, United Kingdom;
²Department of Earth Sciences, University College London, WC1E 6BT London, United Kingdom;
³School of Geographical Sciences, University of Bristol, BS8 1TH Bristol, United Kingdom

The Cretaceous/Paleogene mass extinction, 66 Ma, included the demise of non-avian dinosaurs. Intense debate has focused on the relative roles of Deccan volcanism and the Chicxulub asteroid impact as kill mechanisms for this event. Here, we combine fossil-occurrence data with paleoclimate and habitat suitability models to evaluate dinosaur habitability in the wake of various asteroid impact and Deccan volcanism scenarios. Asteroid impact models generate a prolonged cold winter that suppresses potential global dinosaur habitats. Conversely, long-term forcing from Deccan volcanism (carbon dioxide [CO₂]-induced warming) leads to increased habitat suitability. Short-term (aerosol cooling) volcanism still allows equatorial habitability. These results support the asteroid impact as the main driver of the non-avian dinosaur extinction. By contrast, induced warming from volcanism mitigated the most extreme effects of asteroid impact, potentially reducing the extinction severity.

¹V. Payré,¹K. L. Siebach,¹R. Dasgupta,²A. Udry,³E. B. Rampe,⁴S. M. Morrison
Journal of Geophysical Research (Planets) (In Press) Link to Article [https://doi.org/10.1029/2020JE006467]
¹Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, TX, USA
²Department of Geoscience, University of Nevada, Las Vegas, NV, USA
³Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston, TX, USA
⁴Geophysical Laboratory, Carnegie Institution for Science, Washington, D.C., USA
Published by arrangement with John Wiley & Sons

Understanding magmatic processes is critical to understanding Mars as a system, but Curiosity’s investigation of dominantly sedimentary rocks has made it difficult to constrain igneous processes. Igneous classification of float rocks is made difficult by: (1) the possibility that they have been affected by sedimentary processes or weathering, and (2) grain size heterogeneity in the observed rock textures makes the small‐scale compositions measured by rover instruments unreliable for bulk classification We avoid these ambiguities by using detrital igneous mineral chemistry to constrain models of magmatic processes in the source region for the fluvio‐deltaic Bradbury group. Mineral chemistry is obtained from X‐ray diffraction of three collected samples and a new stoichiometric and visual filtering of ~5,000 laser induced breakdown spectroscopy (LIBS) spots to identify compositions of individual igneous minerals. Observed mineral chemistries are compared to those produced by MELTS thermodynamic modeling to constrain possible magmatic conditions. Fractionation of two starting primary melts derived from different extent of adiabatic decompression melting of a primitive mantle composition could result in the crystallization of all minerals observed. Crystal fractionation of a subalkaline and an alkaline magma is required to form the observed minerals. These results are consistent with the collection of alkaline and subalkaline rocks from Gale as well as clasts from the martian meteorite Northwest Africa 7034 and paired stones. This new method for constraining magmatic processes will be of significant interest for the Mars2020 mission, which will also investigate an ancient volcaniclastic‐sedimentary environment and will include a LIBS instrument.

^1,2Matthew A. Siegler,^1,2Jianqing Feng,³Paul G. Lucey,^1,2Rebecca R. Ghent,⁴Paul O. Hayne,¹Mackenzie N. White
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2020JE006405]
¹Planetary Science Institute, USA
²Southern Methodist University, USA
³University of Hawaii, USA
⁴University of Colorado, Boulder, USA
Published by arrangement with John Wiley & Sons

Passive microwave frequency (~300 MHz‐300 GHz) observations of the Moon have a long history and have been suggested as a plausible orbital instrument for the Moon and other bodies. However, global, orbital multi‐frequency measurements of lunar passive microwave emission have only recently been made by the Chinese Chang’E 1 and 2 Microwave RadioMeter instruments (MRM). These missions carried nearly identical 4‐channel (3.0, 7.8, 19.35, and 37 GHz) instruments into lunar orbit in 2007‐2009 and 2010‐2011, respectively. Over the same time period, the ongoing Lunar Reconnaissance Orbiter mission carried the Diviner Lunar Radiometer, which collected surface temperature measurements in the far‐infrared (~7.8‐400μm) from 2009 to present. By combining these data and associated thermal models, we provide new constraints on the relationship between physical temperature and microwave brightness temperature to reveal novel information about regolith thermal and dielectric properties which can reveal unique geologic information about the Moon. Here we describe several first‐order global results to come from this combined data set, focusing primarily on the ability to detect, map and quantify dielectric loss tangent variations of the Moon, including those from the presence of titanium‐bearing ilmenite. We update the loss tangent models for both highlands and mare and identify a clear frequency dependence that differs in sign between the two. We use the correlation with visible wavelength TiO₂ mapping to provide a means to separate out the loss from rocks and from that of composition.

^1,2,3Sen Hu,⁴Yang Li,¹Lixin Gu,¹Xu Tang,¹Ting Zhang,⁵Akira Yamaguchi,^1,2,3 Yangting Lin,¹Hitesh Changela
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.07.021]
¹Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
²Innovation Academy for Earth Science, Chinese Academy of Sciences, Beijing 100029, China
³College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
⁴Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
⁵National Institute of Polar Research, Tokyo 190-8518, Japan
Copyright Elsevier

We report occurrences of coesite in a martian meteorite, expending previously-reported silica polymorphs such as stishovite (El Goresy et al., 2000), seifertite (Goresy et al., 2008; Sharp et al., 1999), and post-stishovite (El Goresy et al., 2000). The coesite was found in the shock-induced melt regions of NWA 8657, usually coexisting with deformed quartz and silica glass. Three morphological types of coesite have been identified: (I) in a silica-maskelynite assemblage, (II) needle grains, and (III) granular grains embedded in maskelynite. Transmission Electron Microscopy (TEM) shows that all types of coesite appear distributed in silica glass and/or nano-phase maskelynite. The stishovite-like morphology of Type II coesite and the presence of deformed quartz suggest coesite to have inverted from stishovite during decompression. The impact-induced peak pressures and temperatures are estimated at ∼ 18-30 GPa and ∼ 2000 ℃ respectively, based on static high pressure experiments (Langenhorst and Deutsch, 2012; Zhang et al., 1996). The polymorphs aggregates of silica in NWA 8657 indicate that the shock-induced melts in this meteorite cooled slower than those in other stishovite-bearing martian meteorites, but fast enough to preserve coesite.

¹Andrew G.Tomkins,¹Sarah L.Alkemade,¹Sophie E.Nutku,²Natasha R.Stephen,¹Melanie A.Finch,³Heejin Jeon
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.07.022]
¹School of Earth, Atmosphere and Environment, Monash University, Melbourne, Victoria 3800, Australia
²Plymouth Electron Microscopy Centre, University of Plymouth, Drake Circus, Plymouth, Devon, PL4 8AA, United Kingdom
³Centre for Microscopy, Characterisation and Analysis, University of Western Australia, 35 Stirling Highway, Perth, Western Australia 6009, Australia
Copyright Elsevier

The past Martian atmosphere is often compared to the Archean Earth’s as both were dominated by CO₂-rich and O₂-poor chemistries. Archean Earth rocks preserve mass-independently fractionated sulfur isotopes (S-MIF; non-zero Δ³³S and Δ³⁶S), originating from photochemistry in an anoxic atmosphere. Thus, Martian crustal rocks might also be expected to preserve a S-MIF signature, providing insights into past atmospheric chemistry. We have used secondary ion mass spectrometry (SIMS) to investigate in situ, the sulfur isotope systematics of NWA 8171 (paired to NWA 7034), a Martian polymict breccia containing pyrite that formed through hydrothermal sulfur addition in a near-surface regolith setting. In this meteorite, pyrite grains have a weighted mean of Δ³³S of -0.14 ± 0.08 ‰ and Δ³⁶S = -0.70 ± 0.40 ‰ (2 s.e.m.), so the S-MIF signature is subtle. Sulfur isotope data for four additional shergottites yield Δ³³S values that are not resolvable from zero, as in previous studies of shergottites. At first glance the result for the polymict breccia might seem surprising, but no Martian meteorite yet has yielded a S-MIF signature akin to the large deviations seen on Earth. We suggest that S-MIF-bearing aerosols (H₂SO₄ and S₈) were produced when volcanic activity pushed a typically oxidising Martian atmosphere into a reduced state. After rain-out of these aerosols, S₈ would tend to be oxidised by chlorate, dampening the S-MIF signal, which might be somewhat retained in the more abundant photolytic sulfate. Then in the regolith, mixing of aqueous surface-derived sulfate with igneous sulfide (the latter with zero MIF), to form the abundant pyrite seen in NWA 8171, would further dampen the S-MIF signal. Nonetheless, the small negative Δ³³S anomalies seen in Martian meteorites imply that volcanic activity was sufficient to produce a reducing atmosphere at times. This volcanically-driven atmospheric evolution would tend to produce high levels of carbonyl sulfide (OCS). Given that OCS is a relatively long-lived strong greenhouse gas, the S-MIF signal implies that volcanism periodically generated warmer conditions, perhaps offering an evidence-based solution to the young wet Mars paradox.

¹Molly C.McCanta,²M. Darby Dyar
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113978]
¹Department of Earth and Planetary Sciences, University of Tennessee, 1621 Cumberland Ave, Knoxville, TN 37996, United States of America
²Department of Astronomy, Mount Holyoke College, 50 College St, South Hadley, MA 01075, United States of America
Copyright Elsevier

Pyroxene spectral features in the visible near-infrared (VNIR) and mid-infrared (MIR) wavelengths are affected by oxidation resulting from traditional metamorphic processes as well as impact metamorphism. The observed effects are due to modifications in the crystal arising from changes in crystallization temperature or pressure or from substituting Fe³⁺ for Fe²⁺. Highly oxidized pyroxenes from terrestrial mantle xenoliths and shock experiments indicate that the spectral effects of oxidation are greater in clinopyroxene than orthopyroxene because clinopyroxene can accommodate more Fe³⁺ structurally. Changes in clinopyroxene VNIR related to increasing oxidation include a shift in the 0.8 μm absorption band to shorter wavelengths and a strengthening of the Fe²⁺↔Fe³⁺ intervalence charge transfer (IVCT) band, which reduces the band depth of the 1.0 μm feature by ~20%. Although shocked clinopyroxenes are oxidized to similar levels to that seen in the mantle xenoliths, the effects of shock overprint those of oxidation in the VNIR. These include a decrease of ~76% intensity of the 2.35 μm feature and a decrease of ~70% intensity of the 1.0 μm feature. In the MIR, the effects of oxidation and shock are minimal, resulting in a 5% overall decrease in band depth. These shifts and changes can be interpreted as a result of changes in the polyhedra surrounding the Fe cations which reduce crystal field splitting and the order of the crystal structure. Determination of planetary surface composition through VNIR remote sensing methods requires careful consideration of potential changes induced via shock and/or oxidation processes.

¹Brendan A.Anzures,¹Stephen W.Parman,¹Ralph E.Milliken,²Olivier Namur,³Camille Cartier,⁴Sicheng Wang
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.07.024]
¹Brown University, Department of Earth and Planetary Sciences, USA
²KU Leuven, Department of Earth and Environmental Sciences, Belgium
³CRPG/CNRS, University of Lorraine, France
⁴Centre for Mined Land Rehabilitation, Sustainable Minerals Institute, The University of Queensland, Brisbane 4072, Australia
Copyright Elsevier

The NASA MESSENGER mission revealed that lavas on Mercury are enriched in sulfur (1.5-4 wt.%) compared with other terrestrial planets (<0.1 wt.%), a result of high S solubility under its very low oxygen fugacity (estimated ƒO₂ between IW-3 and IW-7). Due to decreasing O availability at these low ƒO₂conditions, and an abundance of S^2-, the latter acts as an important anion. This changes the partitioning behaviour of many elements (e.g. Fe, Mg, and Ca) and modifies the physical properties of silicate melts. To further understand S solubility and speciation in reduced magmas, we have analysed 11 high pressure experiments run at 1 GPa in a piston cylinder at temperatures of 1250 to 1475 °C and ƒO₂ between IW-2.5 to IW-7.5. S K-Edge XANES is used to determine coordination chemistry and oxidation state of S species in highly reduced quenched silicate melts. As ƒO₂ decreases from IW-2 to IW-7, S speciation goes through two major changes. At ∼IW-2, FeS, FeCr₂S₄, Na₂S, and MnS species are destabilized, CaS (with minor Na₂S) becomes the dominant S species. At ∼ IW-4, Na₂S is destabilized, MgS becomes the dominant S species, with lesser amounts of CaS. The changes in S speciation at low ƒO₂affect the activities of SiO₂, MgO and CaO in the melt, stabilizing enstatite at the expense of forsterite, and destabilizing plagioclase and clinopyroxene. These shifts cause the initial layering of Mercury’s solidified magma ocean to be enstatite-rich and plagioclase poor. Our results on S speciation at low ƒO₂ are also applicable to the petrologic evolution of enstatite chondrite parent bodies and perhaps early Earth.

^1,2Micah J. Schaible,³Menelaos Sarantos,⁴Brendan A. Anzures,⁴Stephen W. Parman,^1,2,5Thomas M. Orlando
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2020JE006479]
¹School of Chemistry and Biochemistry, Georgia Institute of Technology
²Center for Space Technology and Research, Georgia Institute of Technology
³Heliophysics Science Division, NASA Goddard Space Flight Center
⁴Department of Earth, Environmental and Planetary Sciences, Brown University
⁵School of Physics, Georgia Institute of Technology
Published by arrangement with John Wiley & Sons

Mercury has a relatively high sulfur content on its surface, and a signal consistent with ionized atomic sulfur (S⁺) was observed by the fast ion plasma spectrometer (FIPS) instrument on the MESSENGER spacecraft. To help confirm this assignment and to better constrain the sources of exospheric sulfur at Mercury, 193 nm photon stimulated desorption (PSD) of neutral sulfur atoms (S⁰) from MgS substrates was studied using resonance enhanced multiphoton ionization (REMPI) and time‐of‐flight (TOF) mass spectrometry. Though the PSD process is inherently non‐thermal, the measured velocities of ejected S⁰ were fit using flux weighted Maxwellian distributions with translation energies ˂E> expressed as translational “temperatures” T _t = ˂E>/μk_B. A bi‐modal distribution consisting of both thermal (T _t = 300 K ) and supra‐thermal (T _t >1000 K ) components in roughly a 2:1 ratio was found to best fit the data. The PSD cross‐section was measured to be approximately 4×10^‐22 cm ² and, together with the velocity distributions, was used to calculate the PSD source rate of S⁰ into the exosphere of Mercury. Exosphere simulations using the calculated rates demonstrate that PSD is likely the primary source of S⁰ in Mercury’s exosphere at low (<1000 km ) altitudes.