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]

¹Varun G. Paul,¹David J. Wronkiewicz, ²Melanie R. Mormile, ³Jamie S. Foster
¹Department of Geological Sciences, Missouri University of Science and Technology, Rolla, Missouri.
²Department of Biological Sciences, Missouri University of Science and Technology, Rolla, Missouri.
³Department of Microbiology and Cell Science, University of Florida, Space Life Science Lab, Merritt Island, Florida.

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Reference
Paul VG, Wronkiewicz DJ, Mormile MR, Foster JS (2016) Mineralogy and Microbial Diversity of the Microbialites in the Hypersaline Storr’s Lake, the Bahamas. Astrobiology 16, 4 282-300
Link to Article [doi:10.1089/ast.2015.1326]

¹Jessica J. Barnes, ^1,2Romain Tartèse, ^1,3Mahesh Anand, ⁴Francis M. McCubbin, ⁵Clive R. Neal, ¹Ian A. Franchi
¹Planetary & Space Sciences, The Open University, Walton Hall, MK7 6AA, UK
²Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Muséum National d’Histoire Naturelle, Sorbonne Universités, CNRS, UPMC & IRD, 75005 Paris, France
³Earth Sciences department, Natural History Museum, London, SW7 5BD, UK
⁴NASA Johnson Space Center, Mailcode XI2, 2101 NASA Parkway, Houston, TX 77058, USA
⁵Department of Civil & Environmental Engineering & Earth Science, University of Notre Dame, IN 46556, USA

Current models for the Moon’s formation have yet to fully account for the thermal evolution of the Moon in the presence of H2O and other volatiles. Of particular importance is chlorine, since most lunar samples are characterised by unique heavy δ37Cl values, significantly deviating from those of other planetary materials, including Earth, for which δ37Cl values cluster around ∼0‰. In order to unravel the cause(s) of the Moon’s unique chlorine isotope signature, we performed a comprehensive study of high-precision in situ Cl isotope measurements of apatite from a suite of Apollo samples with a range of geochemical characteristics and petrologic types. The Cl-isotopic compositions measured in lunar apatite in the studied samples display a wide range of δ37Cl values (reaching a maximum value of +36‰), which are positively correlated with the amount of potassium (K), Rare Earth Element (REE) and phosphorous (P) (KREEP) component in each sample. Using these new data, integrated with existing H-isotope data obtained for the same samples, we are able to place these findings in the context of the canonical lunar magma ocean (LMO) model. The results are consistent with the urKREEP reservoir being characterised by a δ37Cl ∼+30‰. Such a heavy Cl isotope signature requires metal-chloride degassing from a Cl-enriched urKREEP LMO residue, a process likely to have been triggered by at least one large crust-breaching impact event that facilitated the transport and exposure of urKREEP liquid to the lunar surface.

Reference
Barnes JJ, Tartèse R, Anand M, McCubbin FM, Neal CR, Franchi IA (2016) Early degassing of lunar urKREEP by crust-breaching impact(s). Earth and Planetary Science Letters 447, 84–94
Link to Article [doi:10.1016/j.epsl.2016.04.036]
Copyright Elsevier

¹Janice L. Bishop, ²Elizabeth B. Rampe
¹SETI Institute, Carl Sagan Center, 189 Bernardo Ave., Mountain View, CA 94043, United States
²Aerodyne Industries, Jacobs-JETS at NASA JSC, Houston, TX 77058, United States

Layered outcrops in the Mawrth Vallis region of Mars contain the greatest diversity of aqueous alteration products on the planet, and these materials are used to infer past aqueous environments. Orbital investigations indicate Al/Si-rich clay-bearing units overly an Fe/Mg-smectite-rich unit. Many different secondary minerals have been identified in the upper Al/Si-rich clay units, but the presence of poorly crystalline phases has not been previously investigated. Identification of ∼10–30% allophane and imogolite in the clay-bearing units resolves previous mineralogical discrepancies between TES and CRISM of clay-bearing units on Mars. We demonstrate here that the poorly crystalline aluminosilicates allophane and imogolite comprise a significant portion of the uppermost stratum of the Al/Si-clay-rich units. These phases are unique to immature soils derived from volcanic ash in well-drained, mildly acidic environments on Earth, and we hypothesize that the deposits discovered here originate from supervolcanic activity in nearby Arabia Terra. The transition through time from smectite-bearing units to the uppermost allophane/imogolite unit in Mawrth Vallis signifies a change in climate from a warm and wet environment to one where water was sporadic and likely depleted rapidly.

Reference
Bishop JL, Rampe EB (2016) Evidence for a changing Martian climate from the mineralogy at Mawrth Vallis. Earth and Planetary Science Letters 448,42–48
Link to Article [doi:10.1016/j.epsl.2016.04.031]
Copyright Elsevier

¹Olivier Namur, ²Bernard Charlier, ¹Francois Holtz, ²Camille Cartier, ³Catherine McCammon
¹Leibniz University of Hannover, Institute of Mineralogy, 30167 Hannover, Germany
²University of Liege, Department of Geology, 4000 Liege, Belgium
³Bayerisches Geoinstitut, University of Bayreuth, 95440 Bayreuth, Germany

Chemical data from the MESSENGER spacecraft revealed that surface rocks on Mercury are unusually enriched in sulfur compared to samples from other terrestrial planets. In order to understand the speciation and distribution of sulfur on Mercury, we performed high temperature (1200–1750 °C), low- to high-pressure (1 bar to 4 GPa) experiments on compositions representative of Mercurian lavas and on the silicate composition of an enstatite chondrite. We equilibrated silicate melts with sulfide and metallic melts under highly reducing conditions (IW-1.5 to IW-9.4; IW = iron-wüstite oxygen fugacity buffer). Under these oxygen fugacity conditions, sulfur dissolves in the silicate melt as S2−S2− and forms complexes with Fe2+Fe2+, Mg2+Mg2+ and Ca2+Ca2+. The sulfur concentration in silicate melts at sulfide saturation (SCSS) increases with increasing reducing conditions (from 10 wt.% S at IW-8) and with increasing temperature. Metallic melts have a low sulfur content which decreases from 3 wt.% at IW-2 to 0 wt.% at IW-9. We developed an empirical parameterization to predict SCSS in Mercurian magmas as a function of oxygen fugacity (fO2fO2), temperature, pressure and silicate melt composition. SCSS being not strictly a redox reaction, our expression is fully valid for magmatic systems containing a metal phase. Using physical constraints of the Mercurian mantle and magmas as well as our experimental results, we suggest that basalts on Mercury were free of sulfide globules when they erupted. The high sulfur contents revealed by MESSENGER result from the high sulfur solubility in silicate melt at reducing conditions. We make the realistic assumption that the oxygen fugacity of mantle rocks was set during equilibration of the magma ocean with the core and/or that the mantle contains a minor metal phase and combine our parameterization of SCSS with chemical data from MESSENGER to constrain the oxygen fugacity of Mercury’s interior to IW-5.4±0.45.4±0.4. We also calculate that the mantle of Mercury contains 7–11 wt.% S and that the metallic core of the planet has little sulfur (

Reference
Namur O, Charlier B,Holtz F, Cartier C, McCammon C (2016) Sulfur solubility in reduced mafic silicate melts: Implications for the speciation and distribution of sulfur on Mercury. Earth and Planetary Science Letters 448,102–114.
Link to Article [doi:10.1016/j.epsl.2016.05.024]
Copyright Elsevier

¹Derek W.G. Sears
¹Bay Area Environmental Research Institute, NASA Ames Research Center, Space Science and Astrobiology Division (MS 245-3), Mountain View, California 94035, U.S.

Thermoluminescence (TL) properties of 29 CO chondrites from the Miller Range (MIL) and five chondrites from the Dominion Range (DOM) have been measured. MIL has a relatively strong natural TL signal (19.6±14.7 krad), while some of the DOM samples have a very weak natural TL signal ( The CO chondrites: Major Recent Antarctic finds, Their Thermal and Radiation History, and Describing the Metamorphic History of Members of the Class 19.6±14.7 krad), while some of the DOM samples have a very weak natural TL signal (<1 krad) whereas others resemble the MIL meteorites. We argue that MIL and some of the DOM samples had a normal perihelion (∼1.0 AU) and terrestrial age of ∼450-700 ka, while some of the DOM samples have a terrestrial age of ∼100 ka but a perihelion of ∼0.8 AU. The DOM meteorites also show considerable heterogeneity in their induced TL properties, also suggesting that the DOM fragments represent more than one fall. The induced TL data for the MIL samples studied here are consistent with them all being from a single fragmented meteorite. Small (50 mg) chips have TL properties similar to 500 mg chips, so that the smaller chips are representative, although samples taken from original masses less than ∼2 g have low natural TL suggesting that they were heated during atmospheric fall. The properties of CO chondrites are reviewed in terms of their petrologic types. Correlations between TL sensitivity, the most quantitative technique for evaluating metamorphic alteration in CO chondrites, and data for olivine composition and heterogeneity, matrix composition, inert gas content, metal composition (Ni, Co, and Cr in the kamacite), bulk carbon, C and O isotopes, graphite ordering, spectral reflectance at 0.8 μm, and textural characteristics of the amoeboid olivine and Ca-rich inclusions are examined. The petrographic types appear to be largely metamorphic in origin with perhaps a minor role for metasomatism. Contrary to recent proposals it is here argued that petrologic type definitions should (1) be specific enough to be meaningful, but broad enough to be simple in application and robust to new developments, (2) be descriptive and not interpretative, (3) should not oversimplify and obscure important class-to-class differences, and (4) take account of all the available information, while avoiding reliance on any one technique or single observation whose application is based on interpretation. With these considerations in mind the petrographic type definitions for CO chondrites are restated and the petrologic type of 3.2 assigned to both the MIL and DOM CO chondrites.

Reference
Sears WG (2106) The CO chondrites: Major Recent Antarctic finds, Their Thermal and Radiation History, and Describing the Metamorphic History of Members of the Class.
Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.05.033]
Copyright Elsevier

¹Mridusmita Buragohaina, ¹Amit Pathaka, ²Peter Sarreb, ³Takashi Onakac, ³Itsuki Sakonc
¹Department of Physics, Tezpur University, Tezpur 784028, India
²School of Chemistry, The University of Nottingham, University Park, Nottingham, NG7 2RD, United Kingdom
³Department of Astronomy, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan

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Reference
Buragohain M,Pathak A,Sarre P,Onaka T,Sakon I (2016) Mid-infrared vibrational study of deuterium-containing PAH variants. Planetary and Space Science (in Press)
Link to Article [doi:10.1016/j.pss.2016.05.001]

^1,2Yuichiro Cho, ¹Seiji Sugita, ³Yayoi N. Miura, ⁴Ryuji Okazaki, ⁵Naoyoshi Iwata, ⁶Tomokatsu Morota,¹ Shingo Kameda
¹Department of Earth and Planetary Science, University of Tokyo, 7−3−1 Hongo, Bunkyo-ku, Tokyo 113−0033, Japan
²Department of Physics, Rikkyo University, 3−34−1 Nishi-Ikebukuro, Toshima-ku, Tokyo 171−8501, Japan
³Earthquake Research Institute, University of Tokyo, 1−1−1 Yayoi, Bunkyo-ku, Tokyo 113−0032, Japan
⁴Department of Earth and Planetary Sciences, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819−0395, Japan
⁵Department of Earth and Environmental Sciences, Yamagata University, 1–4–12 Kojirakawa, Yamagata 990–8560, Japan
⁶Department of Earth and Environmental Sciences, Nagoya University, Furo, Chikusa, Nagoya, 464−8601, Japan

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Reference
Cho Y, Sugita S, Miura YN, Okazaki R, Iwata N, Morota T, Kameda S (2016) An in-situ K-Ar isochron dating method for planetary landers using a spot-by-spot laser-ablation technique. Planetary and Space Science (in Press)
Link to Article [doi:10.1016/j.pss.2016.05.004]