^1,2,3,4Harold C Connolly, ⁴Dante S Lauretta, ⁵Kevin J Walsh, ⁶Shogo Tachibana, ⁵William F Bottke
¹Earth and Environmental Sciences, The Graduate Center of CUNY, 365 5th Ave, New York 10016, New York, USA
²Department Physical Sciences, Kingsborough Community College of CUNY, 2001 Oriental Blvd, Brooklyn 100235, NY, USA
³Department Earth and Planetary Sciences, AMNH, Central Park West, New York 10024, NY, USA
⁴Lunar and Planetary Laboratory, University of Arizona, Tucson 85721, AZ, USA
⁵Southwest Research Institute, 1050 Walnut St, Suite 300, Boulder 80302, CO, USA
⁶ Department of Natural History Sciences, Hokkaido University, N10W8, Sapporo 060-0810, Japan

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Reference
Connolly HC, Lauretta DS, Walsh KJ, Tachibana S, Bottke WF (2015) Towards understanding the dynamical evolution of asteroid 25143 Itokawa: constraints from sample Analysis. Earth, Planets and Space 67:12
Link to Article [doi:10.1186/s40623-015-0185-3]

¹Kennda L. Lynch, ²Briony H. Horgan, ¹Junko Munakata‐Marr, ³Jennifer Hanley, ⁴Robin J. Schneider, ⁵Kevin A. Rey, ¹John R. Spear, ⁶W. Andrew Jackson, ⁵Scott M. Ritter
¹Department of Civil and Environmental Engineering, Colorado School of Mines, Golden, Colorado, USA
²Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, USA
³Southwest Research Institute, Boulder, Colorado, USA
⁴Department of Chemistry & Geochemistry, Colorado School of Mines, Golden, Colorado, USA
⁵Department of Geological Sciences, Brigham Young University, Provo, Utah, USA
⁶Department of Civil Engineering, Texas Tech University, Lubbock, Texas, USA
Department of Geological Sciences, Brigham Young University, Provo, Utah, USA

The identification and characterization of aqueous minerals within ancient lacustrine environments on Mars is a high priority for determining the past habitability of the red planet. Terrestrial analog studies are useful both for understanding the mineralogy of lacustrine sediments, how the mineralogy varies with location in a lacustrine environment, and for validating the use of certain techniques such as visible-near-infrared spectroscopy (VNIR). In this study, sediments from the Pilot Valley paleolake basin of the Great Salt Lake desert were characterized using visible to near infrared spectroscopy (VNIR) as an analog for Martian paleolake basins. The spectra and subsequent interpretations were then compared to mineralogical characterization by ground truth methods, including X-ray diffraction (XRD), automated scanning electron microscopy (QEMSCAN), and several geochemical analysis techniques. In general, there is good agreement between VNIR and ground truth methods on the major classes of minerals present in the lake sediments and VNIR spectra can also easily discriminate between clay-dominated and salt-dominated lacustrine terrains within the paleolake basin. However, detection of more detailed mineralogy is difficult with VNIR spectra alone as some minerals can dominate the spectra even at very low abundances. At this site, the VNIR spectra are dominated by absorption bands that are most consistent with gypsum and smectites, though the ground truth methods reveal more diverse mineral assemblages that include a variety of sulfates, primary and secondary phyllosilicates, carbonates and chlorides. This study provides insight into the limitations regarding the use of VNIR in characterizing complex mineral assemblages inherent in lacustrine settings.

Reference
Lynch KL, Horgan BH, Munakata‐Marr J, Hanley J, Schneider RJ, Rey KA, Spear JR, Jackson WA, Ritter SM (2015) Near-Infrared Spectroscopy of Lacustrine Sediments in the Great Salt Lake Desert: An Analog Study for Martian Paleolake Basins. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004707]

Published by arrangement with John Wiley&Sons

¹Amanda Albright Olsen,²Elisabeth Hausrath,³J. Donald Rimstidt
¹School of Earth and Climate Sciences, University of Maine, Orono, ME, USA
²Department of Geoscience, University of Nevada, Las Vegas, Las Vegas, NV, USA
³Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA

High salinity brines, although rare on Earth’s surface, may have been important in the geologic history of Mars. Increasing evidence suggests the importance of liquid brines in multiple locations on Mars. In order to interpret the effect of high ionic strength brines on olivine dissolution, which is widely present on Mars, forty-seven new batch reactor experiments combined with 35 results from a previous study conducted at 25°C from 1 < pH < 4 in magnesium sulfate, sodium sulfate, magnesium nitrate, and potassium nitrate solutions with ionic strengths as high as 12 m show that very high ionic strength brines have an inhibitory effect of forsterite dissolution rates. Multiple linear regression analysis of the data suggests that the inhibition in dissolution rates is due to decreased water activity at high ionic strengths. Regression models also show that mMg up to 4 m, and mSO4 up to 3 m have no effect on forsterite dissolution rates. The effect of decreasing dissolution rates with decreasing aH2O is consistent with the idea that water acts as a ligand that participates in the dissolution process. Less available water to participate in the dissolution reaction results in a slower dissolution rate. Multiple linear regression analysis of the data produces the rate equation inline image. Forsterite in dilute solutions with a water activity of one dissolve twice as fast as those in brines with a water activity of 0.8.

Reference
Olsen AA, Hausrath E, Rimstidt JD (2015) Forsterite dissolution rates in Mg-sulfate-rich Mars-analog brines, and implications the aqueous history of Mars. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004664]

Published by arrangement with John Wiley&Sons

¹Kevin M. Cannon, ¹John F. Mustard, ^2,3Carl B. Agee
¹Department of Earth, Environmental and Planetary Sciences, Brown University, Box 1846, RI 02903, United States
²Institute of Meteoritics, University of New Mexico, Albuquerque, NM 87131, United States
³Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, United States

Northwest Africa (NWA) 7034 is the first breccia meteorite from Mars, and unlike the shergottite, nakhlite, and chassignite (SNC) martian meteorites, it matches the estimated chemical composition of martian crust. Here we show that the visible-infrared reflectance spectrum of NWA 7034 is unique compared to other SNCs and is more similar than them to remotely sensed data from Mars, suggesting the martian regolith may contain significant brecciated material produced during heavy bombardment of the crust.

Reference
Cannon KM, Mustard JF, Agee CB (2015) Evidence for a Widespread Basaltic Breccia Component in the Martian Low-Albedo Regions from the Reflectance Spectrum of Northwest Africa 7034. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.01.016]

Copyright Elsevier

¹M.R. Lee, ^1,2T. Tomkinson, ¹L.J. Hallis, ²D.F. Mark
¹School of Geographical and Earth Sciences, University of Glasgow, Gregory Building, Lilybank Gardens, Glasgow G12 8QQ, U.K.
²Scottish Universitites Environmental Research Centre, Rankine Avenue, Scottish Enterprise Technology Park, East Kilbride, G75 0QF, U.K.

The Lafayette meteorite is an olivine clinopyroxenite that crystallized on Mars ∼1300 million years ago within a lava flow or shallow sill. Liquid water entered this igneous rock ∼700 million years later to produce a suite of secondary minerals, collectively called ‘iddingsite’, that occur as veins within grains of augite and olivine. The deuterium/hydrogen ratio of water within these secondary minerals shows that the aqueous solutions were sourced from one or more near-surface reservoirs. Several petrographically distinct types of veins can be recognised by differences in their width, shape, and crystallographic orientation. Augite and olivine both contain veins of a very fine grained hydrous Fe- and Mg-rich silicate that are ∼1-2 micrometres in width and lack any preferred crystallographic orientation. These narrow veins formed by cementation of pore spaces that had been opened by fracturing and probably in response to shock. The subset of olivine-hosted veins whose axes lie parallel to (001) have serrated walls, and formed by widening of the narrow veins by interface coupled dissolution-precipitation. Widening started by replacement of the walls of the narrow precursor veins by Fe-Mg silicate, and a crystallographic control on the trajectory of the dissolution-precipitation front created micrometre-scale {111} serrations. The walls of many of the finely serrated veins were subsequently replaced by siderite, and the solutions responsible for carbonation of olivine also partially recrystallized the Fe-Mg silicate. Smectite was the last mineral to form and grew by replacement of siderite. This mineralization sequence shows that Lafayette was exposed to two discrete pulses of aqueous solutions, the first of which formed the Fe-Mg silicate, and the second mediated replacement of vein walls by siderite and smectite. The similarity in size, shape and crystallographic orientation of iddingsite veins in the Lafayette meteorite and in terrestrial basalts demonstrates a common microstructural control on water-mineral interaction between Mars and Earth, and indicates that prior shock deformation was not a prerequisite for aqueous alteration of the martian crust.

Reference
Lee MR, Tomkinson T, Hallis LJ, Mark DF (2015) Formation of iddingsite veins in the martian crust by centripetal replacement of olivine: Evidence from the nakhlite meteorite Lafayette. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.01.022]

Copyright Elsevier

¹David J. Lawrence, ¹Patrick N. Peplowski, ¹Jeffrey B. Plescia, ²Benjamin T. Greenhagen, ³Sylvestre Maurice, ⁴Thomas H. Prettyman
¹The Johns Hopkins University, Applied Physics Laboratory, Laurel, Maryland, USA
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
³Institut de Recherche en Astrophysique et Planétologie, Toulouse, France
⁴Planetary Science Institute, Tucson, Arizona, USA

A map of bulk hydrogen concentrations in the lunar highlands region is reported. This map is derived using data from the Lunar Prospector Neutron Spectrometer (LP-NS). We resolve prior ambiguities in the interpretation of LP-NS data with respect to non-polar hydrogen concentrations by comparing the LP-NS data with maps of the 750 nanometer albedo reflectance, optical maturity, and the wavelength position of the thermal infrared Christiansen Feature. The best explanation for the variations of LP-NS epithermal neutron data in the lunar highlands is variable amounts of solar-wind-implanted hydrogen. The average hydrogen concentration across the lunar highlands and away from the lunar poles is 65 ppm. The highest hydrogen values range from 120 ppm to just over 150 ppm. These values are consistent with the range of hydrogen concentrations from soils and regolith breccias at the Apollo 16 highlands landing site. Based on a moderate-to-strong correlation of epithermal neutrons and orbit-based measures of surface maturity, the map of highlands hydrogen concentration represents a new global maturity index that can be used for studies of the lunar soil maturation process. We interpret these hydrogen concentrations to represent a bulk soil property related to the long-term impact of the space environment on the lunar surface. Consequently, the derived hydrogen concentrations are not likely related to the surficial enhancements (top tens to hundreds of microns) or local time variations of OH/H2O measured with spectral reflectance data.

Reference
Lawrence DJ, Peplowskia, Plescia JB, Greenhagen BT, Maurice S, Prettyman TH (2015) Bulk Hydrogen Abundances in the Lunar Highlands: Measurements from Orbital Neutron Data. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.01.005]

Copyright Elsevier

¹C. M. O’D. Alexander, ²R. Bowden, ²M. L. Fogel,³K. T. Howard
¹DTM, Carnegie Institution of Washington, Washington, District of Columbia, USA
²GL, Carnegie Institution of Washington, Washington, District of Columbia, USA
³Kingsborough Community College of the City University of New York, Brooklyn, New York, USA

We report the bulk C abundances, and C and O isotopic compositions of carbonates in 64 CM chondrites, 14 CR chondrites, 2 CI chondrites, LEW 85332 (C2), Kaba (CV3), and Semarkona (LL3.0). For the unheated CMs, the total ranges of carbonate isotopic compositions are δ13C ≈ 25–75‰ and δ18O ≈ 15–35‰, and bulk carbonate C contents range from 0.03 to 0.60 wt%. There is no simple correlation between carbonate abundance and isotopic composition, or between either of these parameters and the extent of alteration. Unless accretion was very heterogeneous, the uncorrelated variations in extent of alteration and carbonate abundance suggests that there was a period of open system behavior in the CM parent body, probably prior to or at the start of aqueous alteration. Most of the ranges in CM carbonate isotopic compositions can be explained by their formation at different temperatures (0–130 °C) from a single fluid in which the carbonate O isotopes were controlled by equilibrium with water (δ18O ≈ 5‰) and the C isotopes were controlled by equilibrium with CO and/or CH4 (δ13C ≈ −33‰ or −20‰ for CO- or CH4-dominated systems, respectively). However, carbonate formation would have to have been inefficient, otherwise carbonate compositions would have resembled those of the starting fluid. A quite similar fluid composition (δ18O ≈ −5.5‰, and δ13C ≈ −31‰ or −17‰ for CO- or CH4-dominated systems, respectively) can explain the carbonate compositions of the CIs, although the formation temperatures would have been lower (~10–40 °C) and the relative abundances of calcite and dolomite may play a more important role in determining bulk carbonate compositions than in the CMs. The CR carbonates exhibit a similar range of O isotopes, but an almost bimodal distribution of C isotopes between more (δ13C ≈ 65–80‰) and less altered samples (δ13C ≈ 30–40‰). This bimodality can still be explained by precipitation from fluids with the same isotopic composition (δ18O ≈ −9.25‰, and δ13C ≈ −21‰ or −8‰ for CO- or CH4-dominated systems, respectively) if the less altered CRs had higher mole fractions of CO2 in their fluids. Semarkona and Kaba carbonates have some of the lightest C isotopic compositions of the meteorites studied here, probably because they formed at higher temperatures and/or from more CO2-rich fluids. The fluids responsible for the alteration of chondrites and from which the carbonates formed were almost certainly accreted as ices. By analogy with cometary ices, CO2 and/or CO would have dominated the trapped volatile species in the ices. The chondrites studied are too oxidized for CO-dominated fluids to have formed in their parent bodies. If CH4 was the dominant C species in the fluids during carbonate formation, it would have to have been generated in the parent bodies from CO and/or CO2 when oxidation of metal by water created high partial pressures of H2. The fact that the chondrite carbonate C/H2O mole ratios are of the order predicted for CO/CO2-H2O ices that experienced temperatures of >50–100 K suggests that the chondrites formed at radial distances of <4–15 AU.

Reference
Alexander CMO’D, Bowden R, Fogel ML, Howard KT (2015) Carbonate abundances and isotopic compositions in chondrites. Meteoritics&Planetary Society (in Press)
Link to Article [DOI: 10.1111/maps.12410]

Published by arrangement with John Wiley&Sons

¹Gian Paolo Sighinolfi, ^2,3Emanuela Sibilia, ¹Gabriele Contini,²Marco Martini
¹Dipartimento di Scienze Chimiche e Geologiche, Università di Modena e Reggio E., Modena, Italy
²Dipartimento di Scienza dei Materiali, Università degli Studi di Milano Bicocca, Milano, Italy
³INFN, Sezione di Milano Bicocca, Milano, Italy

Thermoluminescence (TL) dating has been used to determine the age of the meteorite impact crater at Gebel Kamil (Egyptian Sahara). Previous studies suggested that the 45 m diameter structure was produced by a fall in recent times (less than 5000 years ago) of an iron meteorite impactor into quartz-arenites and siltstones belonging to the Lower Cretaceous Gilf Kebir Formation. The impact caused the complete fragmentation of the impactor, and the formation of a variety of impactites (e.g., partially vitrified dark and light materials) present as ejecta within the crater and in the surrounding area. After a series of tests to evaluate the TL properties of different materials including shocked intra-crater target rocks and different types of ejecta, we selected a suite of light-colored ejecta that showed evidence of strong thermal shock effects (e.g., partial vitrification and the presence of high-temperature and -pressure silica phases). The abundance of quartz in the target rocks, including the vitrified impactites, allowed TL dating to be undertaken. The variability of radioactivity of the intracrateric target rocks and the lack of direct in situ dosimetric evaluations prevented precise dating; it was, however, possible to constrain the impact in the 2000 BC–500 AD range. If, as we believe, the radioactivity measured in the fallback deposits is a reliable estimate of the mean radioactivity of the site, the narrower range 1600–400 BC (at the 2σ confidence level) can be realistically proposed.

Reference
Sighinolfi GP, Sibilia E, Contini G, Martini M (2015) Thermoluminescence dating of the Kamil impact crater (Egypt). Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12417]

Published by arrangement with John Wiley&Sons

¹Pavel P. Povinec et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website
¹Department of Nuclear Physics and Biophysics, Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia

On February 15, 2013, after the observation of a brilliant fireball and a spectacular airburst over the southern Ural region (Russia), thousands of stones fell and were rapidly recovered, bringing some extremely fresh material for scientific investigations. We undertook a multidisciplinary study of a dozen stones of the Chelyabinsk meteorite, including petrographic and microprobe investigations to unravel intrinsic characteristics of this meteorite. We also study the short and long-lived cosmogenic radionuclides to characterize the initial meteoroid size and exposure age. Petrographic observations, as well as the mineral compositions obtained by electron microprobe analyses, allow us to confirm the classification of the Chelyabinsk meteorite as an LL5 chondrite. The fragments studied, a few of which are impact melt rocks, contain abundant shock melt veins and melt pockets. It is likely that the catastrophic explosion and fragmentation of the Chelyabinsk meteoroid into thousands of stones was in part determined by the initial state of the meteoroid. The radionuclide results obtained show a wide range of concentrations of 14C, 22Na, 26Al, 54Mn, 57Co, 58Co, and 60Co, which indicate that the pre-atmospheric object had a radius >5 m, consistent with other size estimates based on the magnitude of the airburst caused by the atmospheric entry and breakup of the Chelyabinsk meteoroid. Considering the observed 26Al activities of the investigated samples, Monte Carlo simulations, and taking into account the 26Al half-life (0.717 Myr), the cosmic-ray exposure age of the Chelyabinsk meteorite is estimated to be 1.2 ± 0.2 Myr. In contrast to the other radionuclides, 14C showed a very large range only consistent with most samples having been exposed to anthropogenic sources of 14C, which we associate with radioactive contamination of the Chelyabinsk region by past nuclear accidents and waste disposal, which has also been confirmed by elevated levels of anthropogenic 137Cs and primordial 40K in some of the Chelyabinsk fragments.

Reference
Povinec PP et al. (2015) Cosmogenic radionuclides and mineralogical properties of the Chelyabinsk (LL5) meteorite: What do we learn about the meteoroid? Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12419]

Published by arrangement with John Wiley&Sons

^1,2A. Calzada-Diaz, ³K. H. Joy, ^1,2I. A. Crawford, ^2,4T. A. Nordheim
¹Department of Earth and Planetary Sciences, Birkbeck College, London, UK
²Centre for Planetary Sciences UCL/Birkbeck, London, UK
³School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, UK
⁴Mullard Space Science Laboratory, University College London, Dorking, UK

Lunar meteorites provide important new samples of the Moon remote from regions visited by the Apollo and Luna sample return missions. Petrologic and geochemical analysis of these meteorites, combined with orbital remote sensing measurements, have enabled additional discoveries about the composition and age of the lunar surface on a global scale. However, the interpretation of these samples is limited by the fact that we do not know the source region of any individual lunar meteorite. Here, we investigate the link between meteorite and source region on the Moon using the Lunar Prospector gamma ray spectrometer remote sensing data set for the elements Fe, Ti, and Th. The approach has been validated using Apollo and Luna bulk regolith samples, and we have applied it to 48 meteorites excluding paired stones. Our approach is able broadly to differentiate the best compositional matches as potential regions of origin for the various classes of lunar meteorites. Basaltic and intermediate Fe regolith breccia meteorites are found to have the best constrained potential launch sites, with some impact breccias and pristine mare basalts also having reasonably well-defined potential source regions. Launch areas for highland feldspathic meteorites are much less well constrained and the addition of another element, such as Mg, will probably be required to identify potential source regions for these.

Reference
Calzada-Diaz A, Joy KH, Crawford IA, Nordheim TA (2015) Constraining the source regions of lunar meteorites using orbital geochemical data. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12412]
Published by arrangement with John Wiley&Sons