¹Peter Hoppe, ¹Jan Leitner, ¹János Kodolányi
Nature Astronomy (in Press) Link to Article [doi:10.1038/s41550-017-0215-0]
¹Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, 55128, Mainz, Germany

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H.B.Franz et al. (>10)
Nature Geoscience (in Press) Link to Article [doi:10.1038/ngeo3002]
¹NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA

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^1,2Haiyang Wang, ^1,2,3Charles H. Lineweaver, ^2,3Trevor R. Ireland
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2017.08.024]
¹Research School of Astronomy and Astrophysics, The Australian National University, Canberra, ACT 2611, Australia
²Planetary Science Institute, The Australian National University, Canberra, ACT 2611, Australia
³Research School of Earth Sciences, The Australian National University, Canberra, ACT 2601, Australia
Copyright Elsevier

To first order, the Earth as well as other rocky planets in the Solar System and rocky exoplanets orbiting other stars, are refractory pieces of the stellar nebula out of which they formed. To estimate the chemical composition of rocky exoplanets based on their stellar hosts’ elemental abundances, we need a better understanding of the devolatilization that produced the Earth. To quantify the chemical relationships between the Earth, the Sun and other bodies in the Solar System, the elemental abundances of the bulk Earth are required. The key to comparing Earth’s composition with those of other objects is to have a determination of the bulk composition with an appropriate estimate of uncertainties. Here we present concordance estimates (with uncertainties) of the elemental abundances of the bulk Earth, which can be used in such studies. First we compile, combine and renormalize a large set of heterogeneous literature values of the primitive mantle (PM) and of the core. We then integrate standard radial density profiles of the Earth and renormalize them to the current best estimate for the mass of the Earth. Using estimates of the uncertainties in i) the density profiles, ii) the core-mantle boundary and iii) the inner core boundary, we employ standard error propagation to obtain a core mass fraction of 32.5 ± 0.3 wt%. Our bulk Earth abundances are the weighted sum of our concordance core abundances and concordance PM abundances. Unlike previous efforts, the uncertainty on the core mass fraction is propagated to the uncertainties on the bulk Earth elemental abundances. Our concordance estimates for the abundances of Mg, Sn, Br, B, Cd and Be are significantly lower than previous estimates of the bulk Earth. Our concordance estimates for the abundances of Na, K, Cl, Zn, Sr, F, Ga, Rb, Nb, Gd, Ta, He, Ar, and Kr are significantly higher. The uncertainties on our elemental abundances usefully calibrate the unresolved discrepancies between standard Earth models under various geochemical and geophysical assumptions.

¹William C. Tucker, ¹Abrar H. Quadery, ¹Alfons Schulte, ^1,3,4Richard G. Blair, ¹William E. Kaden, ^1,2Patrick K. Schelling, ¹Daniel T. Britt
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2017.08.027]
¹Department of Physics, University of Central Florida, Orlando, FL 32816-2385, USA
²Advanced Materials Processing and Analysis Center, University of Central Florida, Orlando, FL 32804, USA
³Cluster for the Rational Design of Catalysts for Energy Applications and Propulsion, University of Central Florida, Orlando, FL 32816, USA
⁴Center for Advanced Turbomachinery and Energy Research, University of Central Florida, Orlando, FL 32816, USA
Copyright Elsevier

It is demonstrated that olivine powders heated to subsolidus temperatures in reducing conditions can develop significant concentrations of  10-50 nm diameter Fe nanoparticles on grain surfaces and that these display strong catalytic activity not observed in powders without Fe nanoparticles. Reduced surfaces were exposed to NH₃, CO, and H₂, volatiles that may be present on the surfaces of comet and volatile-rich asteroids. In the case of NH₃ exposure, rapid decomposition was observed. When exposed to a mixture of CO and H₂, significant coking of the mineral surfaces occurred. Analysis of the mineral grains after reaction indicated primarily the presence of graphene or graphitic carbon. The results demonstrate that strong chemical activity can be expected at powders that contain nanophase Fe particles. This suggests space-weathered mineral surfaces may play an important role in the synthesis and processing of organic species. This processing may be part of the weathering processes of volatile-rich but atmosphereless solar-system bodies.

¹Maïa Kuga, ²Guy Cernogora, ¹Yves Marrocchi, ¹Laurent Tissandier,¹ Bernard Marty
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2017.08.031]
¹CRPG-CNRS, Université de Lorraine, 15 rue Notre Dame des Pauvres, 54500 Vandoeuvre-les-Nancy, France
²LATMOS, Université Versailles St. Quentin, UPMC Univ. Paris 06, CNRS, 11 Bvd. d’Alembert, 78280 Guyancourt, France
Copyright Elsevier

The main carrier of primordial heavy noble gases in chondrites is thought to be an organic phase, known as phase Q, whose precise characterization has resisted decades of investigation. The Q noble gas component shows elemental and isotopic fractionation relative to the Solar, in favor of heavy elements and isotopes. These noble gas characteristics were experimentally simulated using a plasma device called the “Nebulotron”. In this study, we synthesized thirteen solid organic samples by electron-dissociation of CO, in which a noble gas mixture was added. The analysis of their heavy noble gas (Ar, Kr and Xe) contents and isotopic compositions reveals enrichment in the heavy noble gas isotopes and elements relative to the light ones. The isotope fractionation is mass-dependent and is consistent with a mn- type law, where n≥1. Based on a plasma model, we propose that the ambipolar diffusion of ions in the ionized CO gas medium is at the origin of the noble gas isotopic fractionation. In addition, the elemental fractionation of experimental and chondritic samples can be accounted for by the Saha law of plasma equilibrium, which does not depend on the respective noble gas masses but rather on their ionization potentials. Our results suggest that the Q noble gases were trapped into growing organic particles starting from solar gases that were fractionated in an ionized medium by ambipolar diffusion and Saha processes. This would imply that both the formation of chondritic organic matter and the trapping of noble gases took place simultaneously in the ionized areas of the protoplanetary disk.

^1,2Alberto G. Fairén,¹Carolina Gil-Lozano,³Esther R. Uceda,⁴Elisabeth Losa-Adams,⁵Alfonso F. Davila,⁴Luis Gago-Duport
Journal of Geophysical Research, Planets (in Press) Link to Article [DOI: 10.1002/2016JE005229]
¹Centro de Astrobiología (CSIC-INTA), Madrid, Spain
²Department of Astronomy, Cornell University, Ithaca, NY, USA
³Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco Madrid, Spain
⁴Departamento de Geociencias Marinas, Universidad de Vigo, Lagoas Marcosende, Vigo, Spain
⁵NASA Ames Research Center, Moffett Field, CA, USA
Published by arrangement with John Wiley & Sons

Geochemical models of secondary mineral precipitation on Mars generally assume semi-open systems (open to the atmosphere but closed at the water-sediment interface) and equilibrium conditions. However, in natural multicomponent systems, the reactive surface area of primary minerals controls the dissolution rate and affects the precipitation sequences of secondary phases; and simultaneously the transport of dissolved species may occur through the atmosphere-water and water-sediment interfaces. Here we present a suite of geochemical models designed to analyze the formation of secondary minerals in basaltic sediments on Mars, evaluating the role of (i) reactive surface areas and (ii) the transport of ions through a basalt sediment column. We consider fully open conditions, both to the atmosphere and to the sediment, and a kinetic approach for mineral dissolution and precipitation. Our models consider a geochemical scenario constituted by a basin (i.e., a shallow lake) where supersaturation is generated by evaporation/cooling, and the starting point is a solution in equilibrium with basaltic sediments. Our results show that cation removal by diffusion, along with the input of atmospheric volatiles and the influence of the reactive surface area of primary minerals, play a central role in the evolution of the secondary mineral sequences formed. We conclude that precipitation of evaporites finds more restrictions in basaltic sediments of small grain size than in basaltic sediments of greater grain size.

¹Lu Pan, ^1,2Bethany L. Ehlmann, ³John Carter, ⁴Carolyn M. Ernst
Journal of Geophysical Research Planets (in Press) Link to Article [DOI: 10.1002/2017JE005276]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
³Institut d’Astrophysique Spatiale, Orsay, France
⁴The John Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
Published by arrangement with John Wiley & Sons

The basin-filling materials of the northern lowlands, which cover ~1/3 of Mars’ surface, record the long-term evolution of Mars’ geology and climate. The buried stratigraphy was inferred through analyses of impact crater mineralogy, detected using data acquired by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). Examining 1045 impact craters across the northern lowlands, we find widespread olivine and pyroxene and diverse hydrated/hydroxylated minerals, including Fe/Mg smectite, chlorite, prehnite, and hydrated silica. The distribution of mafic minerals is consistent with infilling volcanic materials across the entire lowlands (~1–4⋅107 km3), indicating a significant volume of volatile release by volcanic outgassing. Hydrated/hydroxylated minerals are detected more frequently in large craters, consistent with the scenario that the hydrated minerals are being excavated from deep basement rocks, beneath 1-2 km thick mafic lava flows or volcaniclastic materials. The prevalences of different types of hydrated minerals are similar to statistics from the southern highlands. No evidence of concentrated salt deposits has been found, which would indicate a long-lived global ocean. We also find significant geographical variations of local mineralogy and stratigraphy in different basins (geological provinces), independent of dust cover. For example, many hydrated and mafic minerals are newly discovered within the polar Scandia region (> 60°N), and Chryse Planitia has more mafic mineral detections than other basins, possibly due to a previously unrecognized volcanic source.

^1,2P.M. Ranjith, ^1,2Huaiyu He, ³Bingkui Miao, ¹Fei Su, ^3,4Chuantong Zhang, ³Zhipeng Xia, ³Lanfang Xie, ¹Rixiang Zhu
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2017.08.009]
¹Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, PR China
²University of Chinese Academy of Sciences, Beijing 100049, PR China
³Institute of Meteorites and Planetary Research, Guilin University of Technology, Guilin 541004, PR China
⁴Key Laboratory of Planetray Geological Evolution, Guilin University of Technology, Guilin 541004, PR China

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¹Richard D. Starr et al. (>10)
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2017.08.001]
¹Physics Department, The Catholic University of America, Washington, DC 20064, USA

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¹M.E. Varela, ²S-L. Hwang, ³P. Shen, ⁴H-T. Chu, ⁵T-F. Yui, ⁵Y. Iizuka, ⁶F. Brandstätter, ⁷Y.A. Abdu
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2017.08.027]
¹Instituto de Ciencias Astronómicas de la Tierra y del Espacio (ICATE), Avenida España 1512 sur, J5402DSP, San Juan, Argentina
²Department of Materials Science and Engineering, National Dong Hwa University, Hualien, Taiwan, ROC
³Department of Materials and Optoelectronic Science, National Sun Yat-sen University, Kaohsiung, Taiwan, ROC
⁴Central Geological Survey, PO Box 968, Taipei, Taiwan, ROC
⁵Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan, ROC
⁶Mineralogisch-Petrographische Abteilung, Naturhistorisches Museum, Burgring 7, 1010 Wien, Austria
⁷Department of Applied Physics and Astronomy, University of Sharjah, P.O.Box 27272, Sharjah, United Arab Emirate
Copyright Elsevier

Olivinites, together with olivine megacrysts, are the most magnesian phases found in angrites. Their chemical composition (mg# 90) is out of equilibrium with the groundmass and far away from that of possible precipitates from angrite parent melts. Therefore olivinites, as well as olivine megacrysts, were considered as xenoliths and xenocrysts. We report here a detailed study of five olivinites from the angrite D’Orbigny. Our results indicate that D’Orbigny experienced metasomatic alteration processes, which led to enrichments in FeO and MnO (relative to the original composition), changing the initial Mg-rich composition of the olivines to the one seen now. As this process took place in equilibrium with a chondritic reservoir (e.g., Fe/Mn ratios spreading around primitive values), the primitive (Mg-rich) olivine chemical composition was changed towards a more fayalitic one while preserving a chondritic signature. This chondritic signature was preserved in the Fe/Mn ratio of the olivinites, olivine megacrysts, augite grains in olivinites and groundmass olivine of D’ Orbigny. Therefore the fayalite content of about 35 mol.% that characterizes the groundmass olivine of this rock – as well as other angrites- does not correspond to its original composition but may be the result of a late metasomatic process that affected these rocks. If so, olivinites and Mg-rich olivines might not be compositionally exotic phases but are an early constituent phase that retained the pristine more reducing conditions that have been preserved in some angrites, where they form either a small part of the rock (e.g., Asuka 881371 and D’Orbigny) or the majority of it (NWA 8535).