^1,2Janice L. Bishop, ^3,4Alberto G. Fairén, ⁵Joseph R. Michalski, ⁶Luis Gago-Duport, ⁷Leslie L. Baker, ^8,9Michael A. Velbel, ¹⁰Christoph Gross, ¹¹Elizabeth B. Rampe
Nature Astronomy (in Press) Link to Article [doi:10.1038/s41550-017-0377-9]
¹SETI Institute, Mountain View, CA, USA
²National Aeronautics and Space Administration’s Ames Research Center, Moffett Field, CA, USA
³Centro de Astrobiología (Consejo Superior de Investigaciones Científicas–Instituto Nacional de Técnica Aeroespacial), Madrid, Spain
⁴Cornell University, Ithaca, NY, USA
⁵Department of Earth Sciences & Laboratory for Space Research, University of Hong Kong, Hong Kong, China
⁶University of Vigo, Vigo, Spain
⁷University of Idaho, Moscow, ID, USA
⁸Michigan State University, East Lansing, MI, USA
⁹Smithsonian Institution, Washington, DC, USA
¹⁰Freie Universität Berlin, Berlin, Germany
¹¹National Aeronautics and Space Administration–Johnson Space Center, Houston, TX, USA

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^1,2Margaret M. McAdam, ¹Jessica M. Sunshine, ^3,4Kieren T. Howard, ⁵Conel M. Alexander, ⁶Timothy J. McCoy, ⁷Schelte J. Bus
Icarus 306, 32-49 Link to Article [https://doi.org/10.1016/j.icarus.2018.01.024]
¹University of Maryland, Department of Astronomy, College Park, MD 20740, USA
²Northern Arizona University, Department of Physics and Astronomy, Flagstaff AZ 86011, USA
³American Museum of Natural History, Central Park West & 79th St, New York, NY 10024, USA
⁴Kingsborough Community College, 2001 Oriental Blvd, Brooklyn, NY 11235, USA
⁵Department of Terrestrial Magnetism, Carnegie Institution, 1530 P St NW, Washington, DC 20005, USA
⁶National Museum of Natural History, Smithsonian Institution, 600 Maryland Avenue SW, Washington, DC 20002, USA
¹⁷University of Hawaii, Institute for Astronomy, 2444 Dole St, Honolulu, HI 96822, USA
Copyright Elsevier

Least-processed carbonaceous chondrites (carbonaceous chondrites that have experienced minimal aqueous alteration and thermal metamorphism) are characterized by their predominately amorphous iron-rich silicate interchondrule matrices and chondrule rims. This material is highly susceptible to destruction by the parent body processes of thermal metamorphism or aqueous alteration. The presence of abundant amorphous material in a meteorite indicates that the parent body, or at least a region of the parent body, experienced minimal processing since the time of accretion. The CO chemical group of carbonaceous chondrites has a significant number of these least-processed samples. We present visible/near-infrared and mid-infrared spectra of eight least-processed CO meteorites (petrologic type 3.0–3.1). In the visible/near-infrared, these COs are characterized by a broad weak feature that was first observed by Cloutis et al. (2012) to be at 1.3-µm and attributed to iron-rich amorphous silicate matrix materials. This feature is observed to be centered at 1.4-µm for terrestrially unweathered, least-processed CO meteorites. At mid-infrared wavelengths, a 21-µm feature, consistent with Si–O vibrations of amorphous materials and glasses, is also present. The spectral features of iron-rich amorphous silicate matrix are absent in both the near- and mid-infrared spectra of higher metamorphic grade COs because this material has recrystallized as crystalline olivine. Furthermore, spectra of least-processed primitive meteorites from other chemical groups (CRs, MET 00426 and QUE 99177, and C2-ungrouped Acfer 094), also exhibit a 21-µm feature. Thus, we conclude that the 1.4- and 21-µm features are characteristic of primitive least-processed meteorites from all chemical groups of carbonaceous chondrites. Finally, we present an IRTF + SPeX observation of asteroid (93) Minerva that has spectral similarities in the visible/near-infrared to the least-processed CO carbonaceous chondrites. While Minerva is not the only CO-like asteroid (e.g., Burbine et al., 2001), Minerva is likely the least-processed CO-like asteroid observed to date.

^1,2K.R. Bermingham, ²N. Gussone, ^2,3K. Mezger, ^2,4J. Krause
Geochmica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.01.034]
¹Isotope Geochemistry Laboratory, Department of Geology, University of Maryland, College Park, MD-20740 USA
²Institut für Mineralogie, Westfälische Wilhelms-Universität, Corrensstraße 24, Münster, 48149 Germany
³Institut für Geologie, Universität Bern, Baltzerstrasse 1 + 3, Bern, 3012 Switzerland
⁴Helmholtz-Zentrum Dresden – Rossendorf, Helmholtz Institute Freiberg for Resource Technology, Chemnitzer Straße 40, 09599 Freiberg, Germany
Copyright Elsevier

The Ca isotope composition of meteorites and their components may vary due to mass-dependent and/or -independent isotope effects. In order to evaluate the origin of these effects, five amoeboid olivine aggregates (AOAs), three calcium aluminum inclusions (CAIs), five chondrules (C), a dark inclusion from Allende (CV3), two dark inclusions from North West Africa 753 (NWA 753; R3.9), and a whole rock sample of Orgueil (CI1) were analyzed. This is the first coupled mass-dependent and -independent Ca isotope dataset to include AOAs and dark inclusions. Where sample masses permit, Ca isotope data are reported with corresponding petrographic analyses and rare earth element (REE) relative abundance patterns. The CAIs and AOAs are enriched in light Ca isotopes (δ44/40Ca -5.32 to +0.72, where δ44/40Ca is reported relative to SRM 915a). Samples CAI 5 and AOA 1 have anomalous Group II REE patterns. These REE and δ44/40Ca data suggest that the CAI 5 and AOA 1 compositions were set via kinetic isotope fractionation during condensation and evaporation. The remaining samples show mass-dependent Ca isotope variations which cluster between δ44/40Ca +0.53 and +1.59, some of which are coupled with unfractionated REE abundance patterns. These meteoritic components likely formed through the coaccretion of the evaporative residue and condensate following Group II CAI formation or their chemical and isotopic signatures were decoupled (e.g., via nebular or parent-body alteration). The whole rock sample of Orgueil has a δ44/40Ca +0.67 ±0.18 which is in agreement with most published data. Parent-body alteration, terrestrial alteration, and variable sampling of Ca-rich meteoritic components can have an effect on δ44/40Ca compositions in whole rock meteorites.

Samples AOA 1, CAI 5, C 2, and C 4 display mass-independent 48/44Ca anomalies (ε48/44Ca +6 to +12) which are resolved from the standard composition. Other samples measured for these effects (AOA 5, CAI 1, CAI 2, C 3, D 1, D 2, D 3) possess the same 48/44Ca isotope composition as the standard within analytical uncertainty. These data indicate a heterogeneous distribution of 48Ca in the early solar nebula during formation of CAIs, AOAs, and chondrules. In a δ44/40Ca vs. ε48/44Ca plot, no strong correlation is evident which suggests that the thermal processing event which caused a heterogeneous distribution of ε48/44Ca in the solar nebula is unlikely to be directly related to the thermal processing event that caused coupled REE and Ca mass-dependent isotopic fractionation in meteoritic components.

¹Aaron J. Cavosie, ¹Nicholas E. Timms, ²Timmons M. Erickson, ^3,4Christian Koeberl
Geology (in Press) Link to Article [DOI: https://doi.org/10.1130/G39711.1]
¹The Institute for Geoscience Research (TIGeR), Department of Applied Geology, Curtin University, Perth, WA 6102, Australia
²Lunar and Planetary Institute, Universities Space Research Association, Houston, Texas 77058, USA
³Natural History Museum, 1010 Vienna, Austria
⁴Department of Lithospheric Research, University of Vienna, 1090 Vienna, Austria

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¹J. van de Löcht, ²J.E. Hoffmann, ²C. Li, ³Z. Wang, ²H. Becker, ⁴M.T. Rosing, ¹R. Kleinschrodt, ¹C. Münker
Geology (in Press) Link to Article [DOI: https://doi.org/10.1130/G39709.1]
¹Institut für Geologie und Mineralogie, Universität zu Köln, Zülpicher Straße 49b, 50674 Cologne, Germany
²Institut für Geologische Wissenschaften, Freie Universität Berlin, Malteserstraße 74-100, 12249 Berlin, Germany
³China University of Geosciences, No. 388 Lumo Road, 430074 Wuhan, China
⁴NordCEE (Nordic Center for Earth Evolution), Copenhagen University, Øster Voldgade 3-5, 1350 Copenhagen, Denmark

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¹Yu. V. Erokhin, ¹V. A. Koroteev, ¹V. V. Khiller, ²E. V. Burlakov, ¹K. S. Ivanov, ²D. A. Kleimenov
Doklady Earth Sciences 477, 1441-1444 Link to Article [DOI
https://doi.org/10.1134/S1028334X17120121]
¹Institute of Geology and Geochemistry, Ural Branch Russian Academy of Sciences Yekaterinburg Russia
²Ural Geological Museum Ural State Geological University Yekaterinburg Russia

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¹A.A.Maksimova, ¹M.I.Oshtrakh, ¹A.V.Chukin, ²I.Felner, ¹G.A.Yakovlev, ¹V.A.Semionkin
Spectrochmica Acta Part A: Molecular and Biomolecular Spectroscopy 192, 275-284 Link to Article [https://doi.org/10.1016/j.saa.2017.10.056]
¹Institute of Physics and Technology, Ural Federal University, Ekaterinburg 620002, Russian Federation
²Racah Institute of Physics, The Hebrew University, Jerusalem, Israel

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^1,2W. Neumann,^1,3T. S. Kruijer,²D. Breuer,¹T. Kleine
Journal of Geophysical Research, Planets Link to Article [DOI: 10.1002/2017JE005411]
¹Institut für Planetologie, Westfälische Wilhelms-Universität (WWU), Münster, Deutschland
²Institut für Planetenforschung, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Berlin, Deutschland
³Nuclear and Chemical Sciences Division, Lawrence Livermore National Laboratory, Livermore, California, USA
Published by arrangement with John Wiley & Sons

Iron meteorites provide some of the most direct insights into the processes and timescales of core formation in planetesimals. Of these, group IVB irons stand out by having one of the youngest 182Hf-182W model ages for metal segregation (2.9 ± 0.6 Ma after solar system formation), as well as the lowest bulk sulphur content and hence highest liquidus temperature. Here, using a new model for the internal evolution of the IVB parent body, we show that a single stage of metal-silicate separation cannot account for the complete melting of pure Fe metal at the relatively late time given by the Hf-W model age. Instead, a complex metal-silicate separation scenario is required that includes migration of partial silicate melts, formation of a shallow magma ocean and core formation in two distinct stages of metal segregation. In the first stage, a proto-core formed at ≈1.5 Ma via settling of metal particles in a mantle magma ocean, followed by metal segregation from a shallow magma ocean at ≈5.4 Ma. As these stages of metal segregation occurred at different times, the two metal fractions had different 182W compositions. Consequently, the final 182W composition of the IVB core does not correspond to a single differentiation event, but represents the average composition of early- and late-segregated core fractions. Our best-fit model indicates a ≈100 km radius for the IVB parent body and provides an accretion age of ≈0.1 − 0.5 Ma after solar system formation. The computed solidification time is, furthermore, consistent with the Re-Os age for crystallization of the IVB core.

^1,2O.Ruesch et al (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.01.022]
¹NASA Goddard Space Flight Center/USRA, Greenbelt, MD 20771, USA
²ESTEC, European Space Agency, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
Copyright Elsevier

Vinalia and Cerealia Faculae are bright and salt-rich localized areas in Occator crater on Ceres. The predominance of the near-infrared signature of sodium carbonate on these surfaces suggests their original material was a brine. Here we analyze Dawn Framing Camera’s images and characterize the surfaces as composed of a central structure, either a possible depression (Vinalia) or a central dome (Cerealia), and a discontinuous mantling. We consider three materials enabling the ascent and formation of the faculae: ice ascent with sublimation and carbonate particle lofting, pure gas emission entraining carbonate particles, and brine extrusion. We find that a mechanism explaining the entire range of morphologies, topographies, as well as the common composition of the deposits is brine fountaining. This process consists of briny liquid extrusion, followed by flash freezing of carbonate and ice particles, particle fallback, and sublimation. Subsequent increase in briny liquid viscosity leads to doming. Dawn observations did not detect currently active water plumes, indicating the frequency of such extrusions is longer than years.

¹J.T. Poitras, ¹E.A. Cloutis, ², M.R. Salvatore, ³S.A. Mertzman, ¹D.M. Applin, ¹P. Mann
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.01.023]
¹Department of Geography, University of Winnipeg, Winnipeg MB R3B 2E9 Canada
²Department of Physics & Astronomy, Northern Arizona University, Flagstaff, Arizona, USA 86011
³Department of Earth and Environment, Franklin and Marshall College, Lancaster, Pennsylvania, USA
Copyright Elsevier

We investigated the spectral reflectance properties of minerals under a simulated Martian environment. Twenty-Eight different hydrated or hydroxylated phases of carbonates, sulfates, and silica minerals were selected based on past detection on Mars through spectral remote sensing data. Samples were ground and dry sieved to <45 µm grain size and characterized by XRD before and after 133 days inside a simulated Martian surface environment (pressure 5 torr and CO2 fed). Reflectance spectra from 0.35 to 4 µm were taken periodically through a sapphire (0.35 to 2.5 µm) and zinc selenide (2.5 to 4 µm) window Over a 133-day period. Mineral stability on the Martian surface was assessed through changes in spectral characteristics. Results indicate that the hydrated carbonates studied would be stable on the surface of Mars, only losing adsorbed H2O while maintaining their diagnostic spectral features. Sulfates were less stable, often with shifts in the band position of the SO, Fe, and OH absorption features. Silicas displayed spectral shifts related to SiOH and hydration state of the mineral surface, while diagnostic bands for quartz were stable. Previous detection of carbonate minerals based on 2.3-2.5 µm and 3.4-3.9 µm features appear to be consistent with our results. Sulfate mineral detection is more questionable since there can be shifts in band position related to SO4. The loss of the 0.43 µm Fe3+ band in many of the sulfates indicate that there are fewer potential candidates for Fe3+ sulfates to permanently exist on the Martian surface based on this band. The gypsum sample changed phase to basanite during desiccation as demonstrated by both reflectance and XRD.Silica on Mars has been detected using band depth ratio at 1.91 and 1.96 µm and band minimum position of the 1.4 µm feature, and the properties are also used to determine their age. This technique continues to be useful for positive silica identifications, however, silica age appears to be less consistent with our laboratory data. These results will be useful in spectral libraries for characterizing Martian remote sensed data.