The most popular papers on Cosmochemistry Papers in May were:

1-Comelli D et al. (2016) The meteoritic origin of Tutankhamun’s iron dagger blade. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12664]

2-Cotto-Figueroa D, Asphaug E, Garvie LAJ, Rai A, Johnston J, Borkowski L, Datta S, Chattopadhyay A, Morris MA (2016) Scale-Dependent Measurements of Meteorite Strength: Implications for Asteroid Fragmentation. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.05.003]

3-Needham AW, Messenger S, Han J, Keller LP (2016) Corundum-hibonite inclusions and the environments of high temperature processing in the early solar system. Geochmica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.04.022]

4-Simon JI, Matzel JEP, Simon SB, Ross DK, Weber PK, Grossman L (2016) Oxygen isotopic variations in the outer margins and Wark-Lovering rims of refractory inclusions. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.04.025]

5-Robinson KL, Barnes JJ, Nagashima K, Thomen A, Franchi IA, Huss GR, Anand M, Taylor GJ (2016) Water in evolved lunar rocks: Evidence for multiple reservoirs. Geochimica et Cosmochmica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.05.030]

¹D. Ray, ¹S. Ghosh, ²T.K. Goswami, ³M.J. Jobin
¹PLANEX, Physical Research Laboratory, Ahmedabad 380 009, India
²Department of Applied Geology, Dibrugarh University, Assam, India
³Department of Applied Geology, Pondicherry University, India

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

Reference
Ray D, Ghosh S, Goswami TK, Jobin MJ (2016) Insights into chondrule formation process and shock-thermal history of the Dergaon chondrite (H4-5). Geoscience Frontiers (in Press)
Link to Article [doi:10.1016/j.gsf.2016.02.005]

¹Arvidson RE et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website
¹Department of Earth and Planetary Sciences, Washington University in Saint Louis, St. Louis, Missouri 63130, U.S.A.

Mars Reconnaissance Orbiter HiRISE images and Opportunity rover observations of the ~22 km wide Noachian age Endeavour Crater on Mars show that the rim and surrounding terrains were densely fractured during the impact crater-forming event. Fractures have also propagated upward into the overlying Burns formation sandstones. Opportunity’s observations show that the western crater rim segment, called Murray Ridge, is composed of impact breccias with basaltic compositions, as well as occasional fracture-filling calcium sulfate veins. Cook Haven, a gentle depression on Murray Ridge, and the site where Opportunity spent its sixth winter, exposes highly fractured, recessive outcrops that have relatively high concentrations of S and Cl, consistent with modest aqueous alteration. Opportunity’s rover wheels serendipitously excavated and overturned several small rocks from a Cook Haven fracture zone. Extensive measurement campaigns were conducted on two of them: Pinnacle Island and Stuart Island. These rocks have the highest concentrations of Mn and S measured to date by Opportunity and occur as a relatively bright sulfate-rich coating on basaltic rock, capped by a thin deposit of one or more dark Mn oxide phases intermixed with sulfate minerals. We infer from these unique Pinnacle Island and Stuart Island rock measurements that subsurface precipitation of sulfate-dominated coatings was followed by an interval of partial dissolution and reaction with one or more strong oxidants (e.g., O2) to produce the Mn oxide mineral(s) intermixed with sulfate-rich salt coatings. In contrast to arid regions on Earth, where Mn oxides are widely incorporated into coatings on surface rocks, our results demonstrate that on Mars the most likely place to deposit and preserve Mn oxides was in fracture zones where migrating fluids intersected surface oxidants, forming precipitates shielded from subsequent physical erosion.

Reference
Arvidson RE et al. (2016) High concentrations of manganese and sulfur in deposits on Murray Ridge, Endeavour Crater, Mars. American Mineralogist 101, 1389-1405
Link to Article [http://dx.doi.org/10.2138/am-2016-5599]
Copyright: The Mineralogical Society of America

¹E. Bisceglia, ^1,2G. Micca Longo, ^1,2,3S. Longo
¹Dipartimento di Chimica, Università degli Studi di Bari, via Orabona 4, I-70126 Bari, Italy
²CNR-NANOTEC, Bari section, via Amendola 122/D, I-70126 Bari, Italy
³INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy e-mail:

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Reference
Bisceglia E, Longo GM, Longo S (2016) Thermal decomposition rate of MgCO3 as an inorganic astrobiological matrix in meteorites. International Journal of Astrobiology (in Press)
Link to Article [http://dx.doi.org/10.1017/S1473550416000070]

¹G.M. Marion, ²D.C. Catling, ³J.S. Kargel, ⁴J.K. Crowley
¹Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512, USA.
²Department of Earth & Space Sciences, University of Washington, Seattle, WA 98195, USA.
³Department of Hydrology & Water Resources, University of Arizona, Tucson, AZ 85721, USA.
⁴P.O. Box 344, Lovettsville, VA 20180, USA.

On Mars, evidence indicates widespread calcium sulfate minerals. Gypsum (CaSO4•2H2O) seems to be the dominant calcium sulfate mineral in the north polar region of Mars. On the other hand, anhydrite (CaSO4) and bassanite (CaSO4•0.5H2O) appear to be more common in large sedimentary deposits in the lower latitudes. The tropics are generally warmer and drier, and at least locally show evidence of acidic environments in the past. FREZCHEM is a thermodynamic modeling tool used for assessment of equilibrium involving high salinity solutions and salts, designed especially for low temperatures below 298 K (with one version adapted for temperatures up to 373 K), and we have used it to investigate many Earth, Mars, and other planetary science problems. Gypsum and anhydrite were included in earlier versions of FREZCHEM and our model Mars applications, but bassanite (the CaSO4 hemihydrate) has not previously been included. The objectives of this work are to (1) add bassanite to the FREZCHEM model, (2) examine the environments in which thermodynamic equilibrium precipitation of calcium sulfate minerals would be favored on Mars, and (3) use FREZCHEM to model situations where metastable equilibrium might be favored and promote the formation or persistence of one of these phases over the others in violation of an idealized equilibrium state.

We added a bassanite equation based on high temperatures (343 to 373 K). A Mars simulation was based on a previously published Na-Ca-Mg-Cl-SO4 system over the temperature range of 273 to 373 K. With declining temperatures, the first solid phase under equilibrium precipitation is anhydrite at 373 K, then gypsum forms at 319 K (46 °C), and epsomite (MgSO4•7H2O) at 277 K. This sequence could reflect, for example, the precipitation sequence in a saturated solution that is slowly cooled in a deep, warm aquifer.

Because FREZCHEM is based on thermodynamic equilibrium, a crude approach to problems involving metastable equilibria is available by removing phases that may have kinetically inhibited formation. Removing anhydrite allows bassanite to precipitate at 373 K, followed by gypsum at 351 K (78 °C), and epsomite at 277 K. Removing anhydrite and gypsum allows bassanite to form from 373 to 273 K. But bassanite formation from warm to cold temperatures does not seem appropriate for Mars and Earth.

An explanation for spatial patterns of gypsum, anhydrite, and bassanite on Mars and Earth could be past environmental differences. Anhydrite and bassanite are favored near Mars’ equator with higher temperatures, along with drier, more saline, and more acidic environments. Gypsum would be favored at the lower temperatures in the Mars polar region with wetter, lower salinity, and less acidic environments. On Earth, Ca-sulfate would likely over time largely finish re-precipitating as the more insoluble gypsum. But Mars was not in long-term moderate climates compared to Earth that strongly influenced the dominance of gypsum on Earth. So while temperature and water/acid environments for CaSO4 minerals on Mars may have been a major factor for these precipitations, the short-term moderate climates on Mars may also have influenced the prevalence of higher soluble CaSO4 species in the lower Mars latitudes.

Reference
Marion GM, Catling DC, Kargel JS, Crowley JK (2016) Modeling Calcium Sulfate Chemistries with Applications to Mars. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.05.016]
Copyright Elsevier

¹Renato dos Santos, ^2,3Manish Patel, ⁴Javier Cuadros, ¹Zita Martins
¹Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
²Department of Physical Sciences, The Open University, Milton Keynes MK7 6AA, UK
³Space Science and Technology Division, Rutherford Appleton Laboratory, Harwell, Oxfordshire, UK
⁴Department of Earth Sciences, The Natural History Museum, London SW7 5BD, UK

The detection of organic molecules associated with life on Mars is one of the main goals of future life-searching missions such as the ESA-Roscosmos ExoMars and NASA 2020 mission. In this work we studied the preservation of 25 amino acids that were spiked onto the Mars-relevant minerals augite, enstatite, goethite, gypsum, hematite, jarosite, labradorite, montmorillonite, nontronite, olivine and saponite, and on basaltic lava under simulated Mars conditions. Simulations were performed using the Open University Mars Chamber, which mimicked the main aspects of the Martian environment, such as temperature, UV radiation and atmospheric pressure. Quantification and enantiomeric separation of the amino acids were performed using gas-chromatography-mass spectrometry (GC-MS). Results show that no amino acids could be detected on the mineral samples spiked with 1 μM amino acid solution (0.1 μmol of amino acid per gram of mineral) subjected to simulation, possibly due to complete degradation of the amino acids and/or low extractability of the amino acids from the minerals. For higher amino acid concentrations, nontronite had the highest preservation rate in the experiments in which 50 μM spiking solution was used (5 μmol/g), while jarosite and gypsum had a higher preservation rate in the experiments in which 25 and 10 μM spiking solutions were used (2.5 and 1 μmol/g), respectively. Overall, the 3 smectite minerals (montmorillonite, saponite, nontronite) and the two sulfates (gypsum, jarosite) preserved the highest amino acid proportions. Our data suggest that clay minerals preserve amino acids due to their high surface areas and small pore sizes, whereas sulfates protect amino acids likely due to their opacity to UV radiation or by partial dissolution and crystallization and trapping of the amino acids. Minerals containing ferrous iron (such as augite, enstatite and basaltic lava) preserved the lowest amount of amino acids, which is explained by iron (II) catalysed reactions with reactive oxygen species generated under Mars-like conditions. Olivine (forsterite) preserved more amino acids than the other non-clay silicates due to low or absent ferrous iron. Our results show that D- and L-amino acids are degraded at equal rates, and that there is a certain correlation between preservation/degradation of amino acids and their molecular structure: alkyl substitution in the α-carbon seem to contribute towards amino acid stability under UV radiation. These results contribute towards a better selection of sampling sites for the search of biomarkers on future life detection missions on the surface of Mars.

Reference
dos Santos R, Patel M, Cuadros J, Martins Z (2016) Influence of mineralogy on the preservation of amino acids under simulated Mars conditions. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.05.029]
Copyright Elsevier

¹Jordan D. Kendall, ^1,2H.J. Melosh
¹Department of Physics and Astronomy, Purdue University, 525 Northwestern Ave., West Lafayette, IN 47907, United States
²Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN 47907, United States

The abundance of moderately siderophile elements (“iron-loving”; e.g. Co, Ni) in the Earth’s mantle is 10 to 100 times larger than predicted by chemical equilibrium between silicate melt and iron at low pressure, but it does match expectation for equilibrium at high pressure and temperature. Recent studies of differentiated planetesimal impacts assume that planetesimal cores survive the impact intact as concentrated masses that passively settle from a zero initial velocity and undergo turbulent entrainment in a global magma ocean; under these conditions, cores greater than 10 km in diameter do not fully mix without a sufficiently deep magma ocean. We have performed hydrocode simulations that revise this assumption and yield a clearer picture of the impact process for differentiated planetesimals possessing iron cores with radius = 100 km that impact into magma oceans. The impact process strips away the silicate mantle of the planetesimal and then stretches the iron core, dispersing the liquid iron into a much larger volume of the underlying liquid silicate mantle. Lagrangian tracer particles track the initially intact iron core as the impact stretches and disperses the core. The final displacement distance of initially closest tracer pairs gives a metric of core stretching. The statistics of stretching imply mixing that separates the iron core into sheets, ligaments, and smaller fragments, on a scale of 10 km or less. The impact dispersed core fragments undergo further mixing through turbulent entrainment as the molten iron fragments rain through the magma ocean and settle deeper into the planet. Our results thus support the idea that iron in the cores of even large differentiated planetesimals can chemically equilibrate deep in a terrestrial magma ocean.

Reference
Kendall JD, Melosh HJ (2016) Differentiated planetesimal impacts into a terrestrial magma ocean: Fate of the iron core. Earth and Planetary Science Letters 448, 24–33.
Link to Article [doi:10.1016/j.epsl.2016.05.012]
Copyright Elsevier

¹Jessica J. Barnes, ²David A. Kring, ^1,3Romain Tartèse, ¹Ian A. Franchi, ¹Mahesh Anand ⁴Sara S. Russell
¹Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
²Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, Texas 77058, USA
³Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), Muséum National d’Histoire Naturelle, Sorbonne Universités, CNRS, UMPC & IRD, Paris 75005, France
⁴Earth Sciences Department, Natural History Museum, Cromwell Road, London SW7 5BD, UK Mahesh Anand &

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Reference
Barnes JJ, Kring DA, Tartèse R, Franchi IA, Anand M, Russell SS (2016) An asteroidal origin for water in the Moon. Nature Communications 7, 11684
Link to Article [doi:10.1038/ncomms11684]