¹Ted L. Roush, ^1,2Janice L. Bishop, ^1,2Adrian J. Brown, ¹David F. Blake, ¹Thomas F. Bristow
¹NASA Ames Research Center, Moffett Field, CA 94035-0001
²SETI Institute, Mountain View, CA

Quantitative estimates of clay minerals on the martian surface, via remote sensing observations, provide constraints on activity, timing, duration, and extent of aqueous processes and the geochemical environment in martian history. We describe an analytical study to begin enabling quantitative estimates of phyllosilicates when mixed with martian analog materials. We characterize the chemistry, mineralogy, particle size distribution, and reflectance spectra of the end-member materials: saponite, montmorillonite, pyroxene, and palagonitic soil. Reflectance spectra were obtained for physical mixtures of saponite and montmorillonite with pyroxene, and saponite with palagonitic soil. We analyzed the diagnostic phyllosilicate spectral signatures in the 2.2-2.4 μm wavelength region in detail for the mixtures. This involved fitting the observed ∼2.3 or ∼2.2 μm band depth, associated with the presence of saponite and montmorillonite, respectively, as a function of the abundance of these materials in the mixtures. Based upon the band depth of the spectral features we find that 3-5 wt.% of the clay minerals in the mixture with pyroxene can be recognized and at 25 wt.% their presence is indisputable in the mixtures. When the saponite is mixed with the lower albedo palagonitic soil, its presence is clearly distinguishable via the 1.4 and 2.3 μm features at 25 wt.% abundance. These relationships, between abundance and band depth, provide an ability to quantitatively address the amount of these materials in mixtures. The trends described here provide guidance for estimating t

Reference
Roush TL, Bishop JL, Brown AJ, Blake DF, Bristow TF (2015) Laboratory reflectance spectra of clay minerals mixed with Mars analog materials: Toward enabling quantitative clay abundances from Mars spectra. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.06.035]
Copyright Elsevier

¹Scott Messenger, ¹Keiko Nakamura-Messenger, ¹Lindsay P. Keller, ^1,2Simon J. Clemett
¹Robert M. Walker Laboratory for Space Science, EIS Directorate, Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston, Texas, USA
²ESCG/ERC Inc., Houston, Texas, USA

We performed chemical, mineralogical, and isotopic studies of the first interplanetary dust particles (IDPs) collected in the stratosphere without the use of silicone oil. The collection substrate, polyurethane foam, effectively traps impacting particles, but the lack of an embedding medium results in significant particle fragmentation. Two dust particles found on the collector exhibit the typical compositional and mineralogical properties of chondritic porous interplanetary dust particles (CP-IDPs). Hydrogen and nitrogen isotopic imaging revealed isotopic anomalies of typical magnitude and spatial variability observed in previous CP-IDP studies. Oxygen isotopic imaging shows that individual mineral grains and glass with embedded metal and sulfide (GEMS) grains are dominated by solar system materials. No systematic differences are observed in element abundance patterns of GEMS grains from the dry collection versus silicone oil-collected IDPs. This initial study establishes the validity of a new IDP collection substrate that avoids the use of silicone oil as a collection medium, removing the need for this problematic contaminant and the organic solvents necessary to remove it. Additional silicone oil-free collections of this type are needed to determine more accurate bulk element abundances of IDPs and to examine the indigenous soluble organic components of IDPs.

Reference
Messenger S, Nakamura-Messenger K, Keller LP, Simon J. Clemett SJ (2015) Pristine stratospheric collection of interplanetary dust on an oil-free polyurethane foam Substrate. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12473]
Copyright Elsevier

The most popular papers on Cosmochemistry Papers in May were:

1-Wasserburg GJ, Tripella O, Busso M (2015) Isotope Anomalies in the Fe-group Elements in Meteorites and Connections to Nucleosynthesis in AGB Stars. Astrophysical Journal 805, 7. Link to Article [doi:10.1088/0004-637X/805/1/7]

2-Burkhardt C, Schönbächler M (2015) Intrinsic W nucleosynthetic isotope variations in carbonaceous chondrites: Implications for W nucleosynthesis and nebular vs. parent body processing of presolar materials. Geochimica et Cosmochimica Acta (in Press) Link to Article [doi:10.1016/j.gca.2015.06.012]

3-Chen Y, Liu Y, Guan Y, Eiler JM, Ma C, Rossman GR, Taylor LC (2015) Evidence in Tissint for recent subsurface water on Mars. Earth and Planetary Science Letters 425, 55–63 Link to Article [doi:10.1016/j.epsl.2015.05.004]

4-McCubbin FM, Jones RH (2015) Extraterrestrial Apatite: Planetary Geochemistry to Astrobiology. Elements 11/3, 183-188 Link to Article [doi: 10.2113/gselements.11.3.183]

5-Xiong MY, Shelobolina ES, Roden EE (2015) Potential for Microbial Oxidation of Ferrous Iron in Basaltic Glass. Astrobiology 15(5), 331-340. Link to Article [doi:10.1089/ast.2014.1233]

¹O. Ruesch, ¹H. Hiesinger, ²E. Cloutis, ³L. Le Corre, ¹J. Kallisch, ²P. Mann, ^4,1K. Markus, ¹K. Metzler, ⁵A. Nathues, ³V. Reddy
¹Institut für Planetologie, Westfälische Wilhelms-Universität Münster, 48149 Münster, Germany
²Department of Geography, University of Winnipeg, 515 Portage Avenue Winnipeg, Manitoba R3B 2E9, Canada
³Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719-2395, USA
⁴DLR, Institute of Planetary research, Berlin, Germany
⁵Max-Planck-Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany

The howardite, eucrite and diogenite (HED) meteorites are genetically related and represent the most voluminous group of achondrites. They are the closest analog materials to Vesta and V-type asteroids. Many of these meteorites were the focus of intense petrologic and visible to near infrared spectral studies. As ground-based and orbital observations of basaltic asteroids have increased, an improved understanding of HEDs is needed. For this study, we investigated 24 HED samples, mainly new finds from Northwest Africa (NWA). Visible to near infrared (up to 2.5 μm) spectral measurements under varying illumination and observation geometries were acquired for 4 samples. Phase reddening and bluing (i.e., increase and decrease in spectral slope) is observed for the visible slope as phase angle increase. Monotonic phase reddening can occur for the near infrared slope as phase angle increase. Non-systematic changes with phase angle are found for the band area ratio parameter. At phase angles higher than ∼60°, the decrease of reflectance and decrease of pyroxene bands depth are undistinguishable from admixture of low albedo material to HED samples. To assess the precision of empirical equations relating spectral properties and composition, the pyroxenes, feldspar, and olivine chemistry of the samples was determined. Using previous calibrations, systematic overestimations of the ferrosilite (Fs) and wollastonite (Wo) contents are found, especially in the 15-40 Fs range. To overcome such discrepancies, a new set of empirical equations is proposed. For an application of the new calibration, we selected two compositional end-member areas on Vesta on the basis of their iron content. For the iron-poor terrain we found an average pyroxene composition of Fs30Wo5 and for the iron-rich terrain an average of Fs47Wo14.

Reference
Ruesch O, Hiesinger H, Cloutis E, Le Corre L, Kallisch J, Mann P, Markus K, Metzler K, Nathues A, Reddy V (2015)
Near infrared spectroscopy of HED meteorites: Effects of viewing geometry and compositional variations. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.06.034]

Copyright Elsevier

¹G.H. Howarth, ¹J.F. Pernet-Fisher, ²R.J. Bodnar, ¹L.A. Taylor
¹Planetary Geosciences Institute, Earth and Planetary Sciences Dept., The University of Tennessee, Knoxville, TN, 37996 USA.
²Department of Geosciences, Virginia Tech, Blacksburg, VA i24061, USA

Martian meteorite Northwest Africa 7755 is a new example of an enriched, lherzolitic shergottite, containing some of the coarsest-grained apatite yet identified in shergottite meteorites. Their size has permitted detailed observations of volatile distributions within single grains. We have demonstrated that some apatites have been invaded by shock melts, which act to devolatilize parts of grains, resulting in significant Cl-enrichment in the adjacent regions. The extent of chemical heterogeneity within single grains must be carefully considered in other shergottites, so that the effects of secondary modification of apatites are well-constrained, prior to interpreting the volatile contents and primary magmatic processes. Apatite grains unaffected by shock melts are OH-F enriched and Cl-poor (∼F50Cl14OH36), relative to interstitial apatites reported in other shergottites. The volatile compositions are similar to interstitial apatites reported in terrestrial mafic intrusions. Such apatites in terrestrial intrusions are argued to have formed after significant Cl-loss due to the exsolution and migration of Cl-rich brines. Calculated relative F2, Cl2, and H2O fugacities for NWA 7755 apatites show a trend of degassing rather than fractionation, noted in previous studies. Indeed, we interpret the volatile contents of apatites analyzed in the cumulate shergottite NWA 7755 to represent snapshots of the evolving late-stage residual liquid during exsolution of a Cl-rich brine. This fluid phase has subsequently been lost from an open magma system, migrating upward through the cumulate sequence enriching residual liquids in Cl. Alternatively, it formed a hydrothermal system in the martian crust surrounding the intrusion. Furthermore, by comparison with terrestrial examples, we suggest that the late-stage evolution of volatile-bearing phases in NWA 7755 is similar to that of comparable terrestrial mafic rocks. Primary cumulus apatites are F-rich, whereas interstitial apatites may be either Cl-rich, forming as a result of modification through the interaction with Cl-rich brines, or OH-F-rich forming from a magma having exsolved or degassed a Cl-rich fluid phase.

Reference
Howarth GH, Pernet-Fisher JF, Bodnar RJ, Taylor LA (2015) Evidence for the exsolution of Cl-rich fluids in martian magmas: Apatite petrogenesis in the enriched lherzolitic shergottite Northwest Africa 7755. Geochimica et Cosmochimica (in Press)
Link to Article [doi:10.1016/j.gca.2015.06.031]

Copyright Elsevier

¹J.D. Toner, ¹D.C. Catling, ² B. Light
¹University of Washington, Box 351310, Dept. Earth & Space Sciences, Seattle, WA 98195, USA
²Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle, Washington, USA

The Wet Chemistry Laboratory (WCL) on the Mars Phoenix Lander measured ions in a soil-water extraction and found Na+, K+, H+ (pH), Ca2+, Mg2+, View the MathML sourceSO42-,ClO4-, and Cl–. Equilibrium models offer insights into salt phases that were originally present in the Phoenix soil, which dissolved to form the measured WCL solution; however, there are few experimental datasets for single cation perchlorates (View the MathML sourceClO4-), and none for mixed perchlorates, at low temperatures, which are needed to build models. In this study, we measure ice and salt solubilities in binary and ternary solutions in the Na-Ca-Mg-ClO4 system, and then use this data, along with existing data, to construct a low-temperature Pitzer model for perchlorate brines. We then apply our model to a nominal WCL solution. Previous studies have modeled either freezing of a WCL solution or evaporation at a single temperature. For the first time, we model evaporation at subzero temperatures, which is relevant for dehydration conditions that might occur at the Phoenix site. Our model indicates that a freezing WCL solution will form ice, KClO4, hydromagnesite (3MgCO3·Mg(OH)2·3H2O), calcite (CaCO3), meridianiite (MgSO4·11H2O), MgCl2·12H2O, NaClO4·2H2O, and Mg(ClO4)2·6H2O at the eutectic (209 K). The total water held in hydrated salt phases at the eutectic is ∼1.2 wt. %, which is much greater than hydrated water contents when evaporation is modeled at 298.15 K (∼0.3 wt. %). Evaporation of WCL solutions at lower temperatures (down to 210 K) results in lower water activities and the formation of more dehydrated minerals, e.g. kieserite (MgSO4·H2O) instead of meridianiite. Potentially habitable brines, with awaw>0.6, can occur when soil temperatures are above 220 K and when the soil liquid water content is greater than 0.4 wt. % (View the MathML source100×gH2Ogsoil-1). In general, modeling indicates that mineral assemblages derived from WCL-type solutions are characteristic of the soil temperature, water content, and water activity conditions under which they formed, and are useful as indicators of past environmental conditions.

Reference
Toner JD, Catling DC, Light B (2015) A revised Pitzer model for low-temperature soluble salt assemblages at the Phoenix Site, Mars. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.06.011]

Copyright Elsevier

^1,2Z. Kanuchova, ³R. Brunetto, ^4,5D. Fulvio, ^1,2G. Strazzulla
¹Astronomical Institute of Slovak Academy of Sciences, SK-05960 T. Lomnica, Slovakia
²INAF-Osservatorio Astrofisico di Catania, Via S. Sofia 78, I-95123 Catania, Italy
³Institut d’Astrophysique Spatiale (IAS), Université Paris-Sud, UMR 8617 – CNRS INSU, Bât 121, F-91405 Orsay, France
⁴Laboratory Astrophysics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena, Institute of Solid State Physics, Helmholtzweg 3, 07743 Jena, Germany
⁵Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, Rua Marquês de São Vicente 225, 22451-900, Rio de Janeiro, RJ, Brazil

Asteroid surface space weathering has been investigated both observationally and experimentally, mostly focusing on the effects on the visible-near infrared (VNIR, 0.4-2.5 μm) spectral range. Here we present laboratory near-ultraviolet (NUV, 200-400 nm) reflectance spectra of ion irradiated (30-400 keV) silicates and meteorites as a simulation of solar wind ion irradiation. These results show that the induced alteration can reproduce the spread observed in the VNIR vs. NUV slope diagram for S-type asteroids. In particular, the well-known spectral reddening effect induced in the VNIR range is accompanied by a less known but stronger bluing effect at NUV wavelengths. Such trend was previously identified by Hendrix and Vilas (2006) but only based on the comparison between observations and laboratory spectra of lunar materials. We attribute the NUV bluing, analogously to the VNIR reddening, to the formation of iron nanoparticles accompanied by structural modifications (amorphization) of surface silicates. We expect the evidence of weathering processes in the NUV part of spectra before these effects become observable at longer wavelengths, thus searching for the space weathering effects in the NUV range would allow establishing the extent of space weathering for very young asteroidal families.
It will be important to include in future studies the NUV range both in the observations of specific classes of objects (e.g. the Vestoids) and in the laboratory spectra of meteorites and terrestrial analogues before and after space weather processing.

Reference
Kanuchova Z, Brunetto R, Fulviod D, Strazzulla G (2015) Near-ultraviolet Bluing after Space Weathering of Silicates and Meteorites. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.06.030]

Copyright Elsevier

¹N. Van Roosbroek, ¹V. Debaille, ²L. Pittarello, ^2,3S. Goderis, ⁴M. Humayun, ⁵L. Hecht, ⁶F. Jourdan, ⁷M. J. Spicuzza, ³F. Vanhaecke, ²Ph. Claeys
¹Laboratoire G-Time, Université Libre de Bruxelles, Brussels, Belgium
²Earth System Science, Vrije Universiteit Brussel, Brussels, Belgium
³Department of Analytical Chemistry, Ghent University, Ghent, Belgium
⁴Department of Earth, Ocean & Atmospheric Science and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida, USA
⁵Museum für Naturkunde, Leibniz-Institut für Evolutions-und Biodiversitätsforschung, Berlin, Germany
⁶Department of Applied Geology & JdL CMS, Western Australian Argon Isotope Facility, Curtin University of Technology, Perth, WA, Australia
⁷Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin, USA

A 435 kg piece of the Mont Dieu iron meteorite (MD) contains cm-sized silicate inclusions. Based on the concentration of Ni, Ga, Ge, and Ir (8.59 ± 0.32 wt%, 25.4 ± 0.9 ppm, 61 ± 2 ppm, 7.1 ± 0.4 ppm, respectively) in the metal host, this piece can be classified as a IIE nonmagmatic iron. The silicate inclusions possess a chondritic mineralogy and relict chondrules occur throughout the inclusions. Major element analysis, oxygen isotopic analysis (Δ17O = 0.71 ± 0.02‰), and mean Fa and Fs molar contents (Fa15.7 ± 0.4 and Fs14.4 ± 0.5) indicate that MD originated as an H chondrite. Because of strong similarities with Netschaëvo IIE, MD can be classified in the most primitive subgroup of the IIE sequence. 40Ar/39Ar ages of 4536 ± 59 Ma and 4494 ± 95 Ma obtained on pyroxene and plagioclase inclusions show that MD belongs to the old (~4.5 Ga) group of IIE iron meteorites and that it has not been perturbed by any subsequent heating event following its formation. The primitive character of MD sheds light on the nature of its formation process, its thermal history, and the evolution of its parent body.

Reference
Van Roosbroek N, Debaille V, Pittarello L, Goderis S, Humayun M, Hecht L, Jourdan F, Spicuzza MJ, Vanhaecke F, Claeys Ph (2015) The formation of IIE iron meteorites investigated by the chondrule-bearing Mont Dieu meteorite. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12463]

Published by arrangement with John Wiley & Sons

^1,2,3Erica R. Jawin, ¹Sebastien Besse,⁴Lisa R. Gaddis,⁵Jessica M. Sunshine,³James W. Head, ¹Sara Mazrouei
¹European Space Research and Technology Center, Noordwijk, Netherlands.
²Department of Astronomy, Mount Holyoke College, 50 College Street, South
Hadley, MA 01075, USA.
³Department of Earth, Environmental, and Planetary Sciences, Brown University,
Providence, Rhode Island, USA.
⁴USGS Astrogeology Science Center, Flagstaff, Arizona, USA.
⁵Department of Astronomy, University of Maryland, College Park, Maryland, USA

The localized lunar dark mantle deposits (DMDs) in Alphonsus, J. Herschel, and Oppenheimer craters were analyzed using VIS-NIR spectroscopy data from the Moon Mineralogy Mapper. Spectra of these localized DMDs were analyzed for compositional and mineralogical variations within the deposits and were compared with nearby mare basalt units. Spectra of the three localized DMDs exhibited mafic absorption features indicating iron-rich compositions, although the DMDs were spectrally distinct from nearby mare basalts. All of the DMDs contained spectral signatures of glassy materials, suggesting the presence of volcanic glass in varying concentrations across the individual deposits. In addition, the albedo and spectral signatures were variable within the Alphonsus and Oppenheimer crater DMDs, suggesting variable deposit thickness and/or variations in the amount of mixing with the local substrate. Two previously unidentified localized DMDs were discovered to the northeast of Oppenheimer crater. The identification of high concentrations of volcanic glass in multiple localized DMDs in different locations suggests that the distribution of volcanic glass across the lunar surface is much more widespread than has been previously documented. The presence of volcanic glass implies an explosive, vulcanian eruption style for localized DMDs, as this allows volcanic glass to rapidly quench, inhibiting crystallization, compared to the larger hawaiian-style eruptions typical of regional DMD emplacement where black beads indicate a higher degree of crystallization. Improved understanding of the local and global distribution of volcanic glass in lunar DMDs will further constrain lunar degassing and compositional evolution throughout lunar volcanic history.

Reference
Jawin ER, Besse S, LR Gaddis, Sunshine JM, Head JW, Mazrouei S (2015) Examining spectral variations in localized lunar dark mantle deposits. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004759]

Published by arrangement with John Wiley and Sons

^1,2Francis M. McCubbin,^2,3Rhian H. Jones
¹Institute of Meteoritics, University of New Mexico
Albuquerque, NM 87131, USA
²Department of Earth and Planetary Sciences, University of New Mexico
³School of Earth, Atmospheric and Environmental Sciences, University of Manchester
Manchester, M13 9PL, UK

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

Reference
McCubbin FM, Jones RH (2015) Extraterrestrial Apatite: Planetary Geochemistry to Astrobiology. Elements 11/3, 183-188
Link to Article [doi: 10.2113/gselements.11.3.183]