^1,2,6S. T. Zeegers,^1,4 E. Costantini, ¹D. Rogantini,¹C. P. de Vries,³H. Mutschke,³P. Mohr,⁵F. de Groot,²A. G. G. M. Tielens
Astronomy & Astrophysics 627, A16 Link to Article [DOI ttps://doi.org/10.1051/0004-6361/201935050]
¹SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
²Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
³Astrophysikalisches Institut und Universitäts-Sternwarte (AIU), Schillergäßchen 2-3, 07745 Jena, Germany
⁴Anton Pannekoek Astronomical Institute, University of Amsterdam, PO Box 94249, 1090 GE Amsterdam, The Netherlands
⁵Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, The Netherlands
⁶Academia Sinica, Institute of Astronomy and Astrophysics, 11F Astronomy-Mathematics Building, NTU/AS campus, No. 1, Section 4, Roosevelt Rd., Taipei 10617, Taiwan

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¹P. Thebault,¹Q. Kral
Astronomy & Astrophysics 626, A24 Link to Article [DOI https://doi.org/10.1051/0004-6361/201935341 ]
¹LESIA – Observatoire de Paris, UPMC Université Paris 06, Université Paris-Diderot, Paris, France

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¹Baohua Zhang,^1,2Jianhua Ge,^1,2Zili Xiong,¹Shuangmeng Zhai
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2019JE006194]
¹Key Laboratory for High‐Temperature and High‐Pressure Study of the Earth’s Interior, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, Guizhou, China
²University of Chinese Academy of Sciences, Beijing, China
Published by arrangement with John Wiley & Sons

How water could affect thermal transport properties is a key question which needs to be quantified experimentally when it is incorporated as structurally bound hydroxyl groups in the lattice of mantle minerals. In this study, thermal diffusivity (D) and thermal conductivity (κ) of San Carlos olivine aggregates with various water contents (up to 0.2 wt.% H₂O) were measured simultaneously using transient plane‐source method up to 873 K and 3 GPa. Experimental results demonstrate water content can significantly reduce the thermal diffusivity (D) and thermal conductivity (κ) of olivine aggregate. With the increase of H₂O content from 0.08 wt.% to 0.2 wt.%, the absolute values of D and κ for olivine samples decrease by 5–13% and 17–33% and by 3–8% and 14–21%, respectively. D and κ of olivine aggregate decrease with temperature but increase with pressure. Heat capacity is influenced by pressure negatively. Combining the present data with surface heat flow of the Moon as well as heat production, the calculated temperature profiles provide new constraints on the lunar geotherm and possible H₂O content in the lunar interior.

^1,2,3N.R. Alsaeed,^4,5B.M. Jakosky
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2019JE006066]
¹Department of Astrophysical and Planetary Sciences, University of Colorado Boulder, Boulder, CO, USA
²Laboratory for Atmospheric and Space Physics, Boulder, CO, USA
³Mohammed Bin Rashid Space Center, Dubai, UAE
⁴Laboratory for Atmospheric and Space Physics, Boulder, CO, USA
⁵Department of Geological Sciences, University of Colorado Boulder, Boulder, CO, USA
Published by arrangement with John Wiley & Sons

The current deuterium to hydrogen ratio (D/H) on Mars is enriched by a factor of 5‐6 relative to terrestrial values, suggesting that large amounts of H from water have been lost to space. Loss of H occurs more efficiently than loss of D because H atoms are lighter than D atoms, so the remaining gas becomes enriched in D. We constrain the history of water on Mars using D/H by tracking the supply and loss of H and D in the atmosphere. We examined the evolution of water and D/H from 3.3 Ga to the present, using the measured D/H in an ~3 billion‐year‐old Gale crater mudstone and in the present atmosphere as constraints. We define the boundary conditions by the amount of water present at the surface early in history and the amount of water present today, and incorporate the supply of water from outgassing and loss of H and D to space. The factor‐of‐two enrichment in D/H in the last 3.3 Ga can be produced if loss to space outstrips outgassing. This corresponds to a present‐day 20‐50 m water global equivalent layer (GEL) that is a residual of an initial inventory at 3.3 Ga of 40‐170 m GEL, combined with 5‐100 m GEL outgassed and 20‐220 m GEL lost to space.

^1,2Sterken, V.J.,³Westphal, A.J.,⁴Altobelli, N.,⁵Malaspina, D.,^6,7Postberg, F.
Space Science Reviews 215, 43 Link to Article [DOI: 10.1007/s11214-019-0607-9]
¹Astronomisches Institut Universität Bern (AIUB), Bern, Switzerland
²Institute of Applied Physics (IAP), University of Bern, Bern, Switzerland
³Space Sciences Laboratory, University of California at Berkeley, Berkeley, United States
⁴European Space Agency, ESAC, Madrid, Spain
⁵LASP, University of Colorado, Boulder, United States
⁶Institute of Earth Sciences, University of Heidelberg, Heidelberg, Germany
⁷Institute of Geological Sciences, Freie Universität Berlin, Berlin, Germany

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¹Jianguo Wang,²Lei Zhang,²Li Zhong
IOP Conference Series: Earth and Environmental Science 310, 032004 Link to Article [DOI https://doi.org/10.1088/1755-1315/310/3/032004]
¹Department of Geological Engineering, Qinghai University, Xining 810086, China
²TianShi Culture Development Co., Ltd., Xining 810086, China

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¹Berzin, S.V.,¹Ivanov, K.S.,¹Burlakov, E.V.
Doklady Earth Science 487, 908-910 Link to Article [DOI: 10.1134/S1028334X19080245]
¹Zavaritsky Institute of Geology and Geochemistry, Ural Branch, Russian Academy of Sciences, Yekaterinburg, 620016, Russian Federation

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¹Dominik Talla,¹Manfred Wildner
American Mineralogist 104, 1732-1749 Link to Article [https://doi.org/10.2138/am-2019-6983]
¹Institut für Mineralogie und Kristallographie, Althanstraße 14, 1090 Wien, Austria
Copyright: The Mineralogical Society of America

The investigation of hydrous sulfate deposits and sulfate-cemented soils on the surface of Mars is one of the important topics in the recent scientific endeavor to retrieve detailed knowledge about the planetary water budget and surface weathering processes on our neighbor planet. Orbital visible/near-IR spectra of the surface of Mars indicate kieserite, MgSO4·H2O, as a dominant sulfate species at lower latitudes. However, given the Fe-rich composition of the martian surface, it is very probable that its actual composition lies at an intermediate value along the solid-solution series between the kieserite and szomolnokite (FeSO4·H2O) end-members. Despite the known existence of significant lattice parameter changes and spectral band position shifts between the two pure end-members, no detailed crystal chemical and spectroscopic investigation along the entire kieserite–szomolnokite solid solution range has been done yet.
The present work proves for the first time the existence of a continuous kieserite–szomolnokite solid-solution series and provides detailed insight into the changes in lattice parameters, structural details, and positions of prominent bands in FTIR (5200–400 cm–1) and Raman (4000–100 cm–1) spectra in synthetic samples as the Fe/Mg ratio progresses, at both ambient as well as Mars-relevant lower temperatures. Additionally, an UV-Vis-NIR (29 000–3500 cm–1) crystal field spectrum of szomolnokite is presented to elucidate the influence of Fe2+-related bands on the overtone- and combination mode region.
The kieserite–szomolnokite solid-solution series established in this work shows Vegard-type behavior, i.e., lattice parameters as well as spectral band positions change along linear trends. The detailed knowledge of these trends enables semi-quantitative estimations of the Fe/Mg ratio that can be applied to interpret martian monohydrated sulfates in data from remote sensing missions on a global scale as well as from in situ rover measurements. Given the knowledge of the surface temperature during spectral measurements, the established temperature behavior allows quantitative conclusions concerning the Fe/Mg ratio. Our understanding of the kieserite–szomolnokite solid-solution series will be well applicable to the Mars 2020 and ExoMars 2020 rover missions that will focus on near IR (0.9 to 3.5 μm) and, for the first time on Mars, Raman spectroscopy.

¹Justin I. Simon,^1,2D. Kent Ross,^1,3Ann N. Nguyen,⁴Steven B. Simon,¹Scott Messenger
The Astrophysical Journal, Letters 884, L29 Link to Article [DOI
https://doi.org/10.3847/2041-8213/ab43e4]
¹Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, TX 77058, USA
²University of Texas at El Paso/Jacobs-JETS, Houston, TX 77058, USA
³Jacobs-JETS, Houston, TX 77058, USA
⁴Institute of Meteoritics, University of New Mexico, Albuquerque, NM 87131, USA

A spinel-rich, layered calcium- aluminum-rich spherule from the MIL 090019 CO3 chondrite contains a spinel core with a relatively ¹⁶O-rich (Δ¹⁷O ~ −18‰) and mass-fractionated oxygen isotopic composition surrounded by minerals, including spinel, that are relatively ¹⁶O-poor (Δ¹⁷O ~ −7‰), which are in turn surrounded by layers of ¹⁶O-enriched silicates (Δ¹⁷O ~ −17‰). Inclusions with refractory mineral assemblages such as this one are proposed to record inner nebula processes during the earliest epoch of solar nebula evolution. Mineralogical and textural analyses indicate that this primordial particle formed by high-temperature gas–solid reactions, partial melting, evaporation, and condensation. The radially distributed oxygen isotopic heterogeneity measured among multiple occurrences of several minerals, including spinel, requires the existence of ¹⁶O-poor gas at the beginning of solar system formation, 10⁵ yr earlier than it can be produced by photochemical self-shielding in the solar nebula and introduced to the inner protoplanetary disk.

¹J. J. Bernal,²P. Haenecour,³J. Howe,^2,4T. J. Zega,⁵S. Amari,^1,6,7L. M. Ziurys
The Astrophysical Journal, Letters 883, L43 Link to Article [DOI
https://doi.org/10.3847/2041-8213/ab4206]
¹Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721, USA
²Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Boulevard, Tucson, AZ 85721, USA
³Department of Materials Science and Engineering, and Department of Chemical Engineering and Applied Chemistry, University of Toronto, Canada
⁴Department of Materials Science and Engineering, University of Arizona, USA
⁵Physics Department and McDonnell Center for the Space Sciences, Washington University in St. Louis, 1 Brookings Drive, St. Louis, MO 63130, USA
⁶Department of Astronomy, Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
⁷Arizona Radio Observatory, Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA

We have conducted laboratory experiments with analog crystalline silicon carbide (SiC) grains using transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS). The 3C polytype of SiC was used—the type commonly produced in the envelopes of asymptotic giant branch (AGB) stars. We rapidly heated small (~50 nm) synthetic SiC crystals under vacuum to ~1300 K and bombarded them with 150 keV Xe ions. TEM imaging and EELS spectroscopic mapping show that such heating and bombardment leaches silicon from the SiC surface, creating layered graphitic sheets. Surface defects in the crystals were found to distort the six-membered rings characteristic of graphite, creating hemispherical structures with diameters matching that of C₆₀. Such nonplanar features require the formation of five-membered rings. We also identified a circumstellar grain, preserved inside the Murchison meteorite, that contains the remnant of an SiC core almost fully encased by graphite, contradicting long-standing thermodynamic predictions of material condensation. Our combined laboratory data suggest that C₆₀ can undergo facile formation from shock heating and ion bombardment of circumstellar SiC grains. Such heating/bombardment could occur in the protoplanetary nebula phase, accounting for the observation of C₆₀ in these objects, in planetary nebulae (PNs) and other interstellar sources receiving PN ejecta. The synthesis of C₆₀ in astronomical sources poses challenges, as the assembly of 60 pure carbon atoms in an H-rich environment is difficult. The formation of C₆₀ from the surface decomposition of SiC grains is a viable mechanism that could readily occur in the heterogeneous, hydrogen-dominated gas of evolved circumstellar shells.