Paul D. Spudis^1,*, Dayl J. P. Martin^1,2 and Georgiana Kramer¹

¹Lunar and Planetary Institute, Houston, Texas, USA
²School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, UK

The Orientale Basin is one of the largest (930 km diameter) and youngest (~3.8 Ga) impact craters on the Moon. As the basin is only partly flooded by mare lava, its floor materials expose a major portion of the basin impact melt sheet, which some previous work has suggested might have undergone igneous differentiation. To test this idea, we remapped the geology of the Orientale Basin using images and topography from the Lunar Reconnaissance Orbiter, mineralogical information from the Chandrayaan-1 Moon Mineralogy Mapper, and elemental concentration maps from Clementine multispectral imaging and Lunar Prospector gamma ray data. The Maunder Formation (impact melt sheet of the basin) is uniform in chemical composition (equivalent to “anorthositic norite”) in at least the upper 2 km of the deposit. The deepest sampling of the basin melt sheet (maximum depths of ~3–5 km by the crater Maunder, 55 km in diameter) shows a variety of lithologies, but these rock types (anorthosite, anorthositic norite melt rocks, mare basalt, and gabbro) are not those predicted by the differentiation model. We conclude that no differentiation of the Orientale Basin melt sheet has occurred and that such a process is not evident from new remote sensing data for the Moon or in the Apollo lunar samples.

Reference
Spudis PD, Martin DJP and Kramer G (in press) Geology and composition of the Orientale Basin impact melt sheet. Journal of Geophysical Research: Planets
[doi:10.1002/2013JE004521]
Published by arrangement with John Wiley & Sons

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Julien Stodolna, Zack Gainsforth, Anna L. Butterworth and Andrew J. Westphal

Space Sciences Laboratory, University of California, Berkeley, 7 Gauss Way, Berkeley, CA 94720, USA

We report the presence of preserved primitive fine-grained material containing an enstatite whisker with the crystallographic characteristics of a primary condensate in a sample of the Jupiter-family comet Wild 2, returned to earth by NASAʼs Stardust mission. The preserved primitive material is composed of silica-rich amorphous material embedded with iron sulfides and silicates. It is in close association with a type II chondrule-like object in the track C2052,2,74 (Ogliore et al., 2012). The close association of a chondrule and a primary condensate shows they must have formed in different environments and probably met in the comet-forming region. The first observation of an enstatite whisker with properties indicating primary condensation in a comet is a new link between comets and Chondritic Porous IDPs (CP-IDPs).

Reference
Stodolna J, Gainsforth Z, Butterworth AL and Westphal AJ (2014) Characterization of preserved primitive fine-grained material from the Jupiter family comet 81P/Wild 2 – A new link between comets and CP-IDPs. Earth and Planetary Science Letters 388:367–373.
[doi:10.1016/j.epsl.2013.12.018]
Copyright Elsevier

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José M. Madiedo^a,b, José L. Ortiz^c, Josep M. Trigo-Rodríguez^d, Joan Dergham^d, Alberto J. Castro-Tirado^c, Jesús Cabrera-Caño^b, Pep Pujols^e

^aFacultad de Física. Departamento de Física Atómica, Molecular y Nuclear. Universidad de Sevilla, 4012 Sevilla, Spain
^bFacultad de Ciencias Experimentales. Universidad de Huelva, 21071 Huelva, Spain
^cInstituto de Astrofísica de Andalucía, CSIC, Apt. 3004, Camino Bajo de Huetor 50, 18080 Granada, Spain
^dInstitute of Space Sciences (CSIC-IEEC), Campus UAB, Facultat de Ciències, Torre C5-parell-2ª, 08193 Bellaterra, Barcelona, Spain
^eGrup d’Estudis Astronòmics (GEA) and Agrupació Astronòmica d’Osona, Barcelona, Spain

We present the analysis of five bright fireballs observed over Spain and France between 2010 and 2012. Their absolute magnitude ranged between -9.0 and -11.5. Radiant and orbital data indicate that these events were associated with the Taurid meteoroid stream. Their trajectory in the atmosphere is calculated and the heliocentric orbit of the meteoroids is obtained. The emission spectra produced by three of these fireballs are also discussed, and the chemical nature of the parent impactors is inferred, together with different physical parameters of these particles such as the meteoroid mass and tensile strength. On the basis of these results, the ability of Taurid meteoroids to produce meteorites is discussed.

Reference
Madiedo JM, Ortiz JL, Trigo-Rodríguez JM, Dergham J, Castro-Tirado AJ, Cabrera-Caño J and Pujols P (in press) Analysis of bright Taurid fireballs and their ability to produce meteorites. Icarus
[doi:10.1016/j.icarus.2013.12.025]
Copyright Elsevier

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Arya Udry*, J. Brian Balta, Harry Y. McSween Jr.

Planetary Geosciences Institute, Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Tennessee, USA

Martian primary compositions, i.e., magmas that did not experience fractionation and/or contamination after extraction from the mantle, occur as a subset of Martian meteorites and a few lavas analyzed on the planet’s surface by rovers. Eruptions of primary magmas are rare on Earth and presumably on Mars. Previous studies of fractional crystallization of Martian primary magmas have been conducted under isobaric conditions, simulating idealized crystallization in magma chambers. Polybaric fractionation, which occurs during magma ascent, has not been investigated in detail for Martian magmas. Using the MELTS algorithm and the pMELTS revision, we present comprehensive isobaric and polybaric thermodynamic calculations of the fractional crystallization of four primary or parental Martian magmas (Humphrey, Fastball, Y-980459 shergottite, and nakhlite parental melts) using various pressure-temperature paths, oxygen fugacities, and water contents to constrain how these magmas might evolve. We then examine whether known Martian alkaline rock compositions could have formed through fractional crystallization of these magmas under the simulated conditions. We find that isobaric and polybaric crystallization paths produce similar residual melt compositions, but given sufficient details, we may be able to distinguish between them. We calculate that Backstay (Gusev Crater) likely formed by fractionation of a primary magma under polybaric conditions, while Jake_M (Gale Crater) may have formed through melting of a metasomatized mantle, crustal assimilation, or fractional crystallization of an unknown primary magma. The best fits for the Backstay composition indicate that consideration of polybaric crystallization paths can help improve the quality of fit when simulating liquid lines of descent.

Reference
Udry A, Balta JB and McSween Jr. HY (in press) Exploring fractionation models for Martian magmas. Journal of Geophysical Research: Planets
[doi:10.1002/2013JE004445]
Published by arrangement with John Wiley & Sons

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Chi Ma*, John R. Beckett and George R. Rossman

Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A.

Monipite (IMA 2007-033), MoNiP, is a new phosphide mineral that occurs as one 1 × 2 μm crystal in a Type B1 Ca-Al-rich inclusion (CAI) ACM-2 from the Allende CV3 carbonaceous chondrite. It has an empirical formula of (Mo_0.84Fe_0.06Co_0.04Rh_0.03)(Ni_0.89Ru_0.09)P, and a P6̄ 2m Fe₂P type structure with a = 5.861, c = 3.704 Å, V = 110.19 ų, and Z = 3. The calculated density using our measured composition is 8.27 g/cm³, making monipite the densest known mineral phosphide. Monipite probably either crystallized from an immiscible P-rich melt that had exsolved from an Fe-Ni-enriched alloy melt that formed during melting of the host CAI or it exsolved from a solidified alloy. Most of the original phosphide in the type occurrence was later altered to apatite and Mo-oxides, leaving only a small residual grain. Monipite occurs within an opaque assemblage included in melilite that contains kamiokite (Fe₂Mo₃O₈), tugarinovite (MoO₂), and a Nb-rich oxide [(Nb,V,Fe)O₂], none of which has previously been reported in meteorites, together with apatite, awaruite (Ni₂Fe), and vanadian magnetite.

Reference
Ma C, Beckett JR and Rossman GR (2014) Monipite, MoNiP, a new phosphide mineral in a Ca-Al-rich inclusion from the Allende meteorite. American Mineralogist 99:198-205.
[doi:10.2138/am.2014.4512]
Copyright: The Mineralogical Society of America

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Alex R. Howe and Roman R. Rafikov

Department of Astrophysical Sciences, Princeton University, Ivy Lane, Princeton, NJ 08540, USA

The Oort cloud remains one of the most poorly explored regions of the solar system. We propose that its properties can be constrained by studying a population of dust grains produced in collisions of comets in the outer solar system. We explore the dynamics of μm-sized grains outside the heliosphere (beyond ~250 AU), which are predominantly affected by the magnetic field of the interstellar medium (ISM) flow past the Sun. We derive analytic models for the production and motion of small particles as a function of their birth location in the cloud and calculate the particle flux and velocity distribution in the inner solar system. These models are verified by direct numerical simulations. We show that grains originating in the Oort cloud have a unique distribution of arrival directions, which should easily distinguish them from both interplanetary and interstellar dust populations. We also demonstrate that the distribution of particle arrival velocities is uniquely determined by the mass distribution and dust production rate in the cloud. Cometary collisions within the cloud produce a flux of μm-sized grains in the inner solar system of up to several m⁻² yr⁻¹. The next generation dust detectors may be sensitive enough to detect and constrain this dust population, which will illuminate the Oort cloud’s properties. We also show that the recently detected mysterious population of large (μm-sized) unbound particles, which seems to arrive with the ISM flow, is unlikely to be generated by collisions of comets in the Oort cloud.

Reference
Howe AR and Rafikov RR (2014) Probing Oort Cloud and Local Interstellar Medium Properties via Dust Produced in Cometary Collisions. The Astrophysical Journal 781:52.
[doi:10.1088/0004-637X/781/1/52]

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David A. McKeown^1,*, Andrew C. Buechele¹, Ryan Tappero², Timothy J. McCoy³ and Kathryn G. Gardner-Vandy³

¹Vitreous State Laboratory, The Catholic University of America, 620 Michigan Avenue NE, Washington, D.C. 20064, U.S.A.
²Photon Sciences Department, Brookhaven National Laboratory, Upton, New York 11793, U.S.A.
³Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560-0119, U.S.A.

Chromium K-edge X-ray absorption spectra were collected to characterize Cr in forsterite (Mg₂SiO₄) as well as sulfides within the MAC 88136 EL3 chondrite to determine Cr valence and to see whether forsterite within this meteorite can be used as a Cr²⁺-silicate standard. Spectra were measured on several areas within a nearly pure 100 × 200 μm forsterite grain containing 0.13 wt% Cr. XANES findings indicate highly reduced Cr²⁺ species, with no clear evidence of Cr³⁺ or Cr⁶⁺. EXAFS data indicate an average 2.02 Å Cr-O nearest-neighbor distance, consistent with Cr-O distances found in square-planar Cr²⁺O₄ sites observed in synthetic crystalline silicates, and an average 2.69 Å Cr-Si second-nearest neighbor distance, consistent with Cr²⁺substituting for Mg²⁺ in the forsterite M(1) site. Nearest-neighbor Debye-Waller factor and coordination number parameters indicate Cr²⁺ is likely entering forsterite in disordered sites that are possible intermediates between M(1) and square-planar Cr²⁺O₄ configurations. Preliminary Cr XAS measurements on sulfides within this meteorite also indicate Cr²⁺ in CrS₆octahedra.

Reference
McKeown DA, Buechele AC, Tappero R, McCoy TJ and Gardner-Vandy KG (2014) X-ray absorption characterization of Cr in forsterite within the MacAlpine Hills 88136 EL3 chondritic meteorite. American Mineralogist 99:190-197.
[doi:10.2138/am.2014.4508]
Copyright: The Mineralogical Society of America

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Nachiketa Rai and Wim van Westrenen

Faculty of Earth and Life Sciences, VU University Amsterdam, 1081 HV, Amsterdam, The Netherlands

Analyses of Apollo era seismograms, lunar laser ranging data and the lunar moment of inertia suggest the presence of a small, at least partially molten Fe-rich metallic core in the Moon, but the chemical composition and formation conditions of this core are not well constrained. Here, we assess whether pressure–temperature conditions can be found at which the lunar silicate mantle equilibrated with a Fe-rich metallic liquid during core formation. To this end, we combine measurements of the metal–silicate partitioning behavior of siderophile elements with the estimated depletion due to core formation in those elements in the silicate mantle of the Moon. We also explore how the presence of the light element sulfur (suggested by seismic models to be present in the core at concentrations of up to 6 wt%) in the lunar core affects core formation models.
We use published metal–silicate partitioning data for Ni, Co, W, Mo, P, V and Cr in the lunar pressure range (1 atm–5 GPa) and characterize the dependence of the metal/silicate partition coefficients (D) on temperature, pressure, oxygen fugacity and composition of the silicate melt and the metal. If the core is assumed to consist of pure iron, core–mantle equilibration conditions that best satisfy lunar mantle depletions of five siderophile elements—Ni, Co, W, Mo and P—are a pressure of 4.5(±0.5) GPa and a temperature of 2200 K. The lunar mantle depletions of Cr and V are also consistent with metal–silicate equilibration in this pressure and temperature range if 6 wt% S is incorporated into the lunar core. Our results therefore suggest that metal–silicate equilibrium during lunar core formation occurred at depths close to the present-day lunar core–mantle boundary. This provides independent support for both the existence of a deep magma ocean in the Moon in its early history and the presence of significant amounts of sulfur in the lunar core.

Reference
Rai N and Westrenen W (2014) Lunar core formation: New constraints from metal–silicate partitioning of siderophile elements. Earth and Planetary Science Letters 388:343–352.
[doi:10.1016/j.epsl.2013.12.001]
Copyright Elsevier

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Juliane Gross^a,b, Allan H. Treiman^b, Celestine N. Mercer^a,1

^aAmerican Museum of Natural History, New York, NY 10024, United States
^bLunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX 77058, United States
¹USGS Denver Federal Center, Denver, CO 80225

The composition of the lunar crust provides clues about the processes that formed it and hence contains information on the origin and evolution of the Moon. Current understanding of lunar evolution is built on the Lunar Magma Ocean hypothesis that early in its history, the Moon was wholly or mostly molten. This hypothesis is based on analyses of Apollo samples of ferroan anorthosites (>90% plagioclase; molarMg/(Mg+Fe)=Mg#<75) and the assumption that they are globally distributed. However, new results from lunar meteorites, which are random samples of the Moonʼs surface, and remote sensing data, show that ferroan anorthosites are not globally distributed and that the Apollo highland samples, used as a basis for the model, are influenced by ejecta from the Imbrium basin. In this study we evaluate anorthosites from all currently available adequately described lunar highland meteorites, representing a more widespread sampling of the lunar highlands than Apollo samples alone, and find that ~80% of them are significantly more magnesian than Apollo ferroan anorthosites. Interestingly, Luna mission anorthosites, collected outside the continuous Imbrium ejecta, are also highly magnesian. If the lunar highland crust consists dominantly of magnesian anorthosites, as suggested by their abundance in samples sourced outside Imbrium ejecta, a reevaluation of the Lunar Magma Ocean model is a sensible step forward in the endeavor to understand lunar evolution. Our results demonstrate that lunar anorthosites are more similar in their chemical trends and mineral abundance to terrestrial massif anorthosites than to anorthosites predicted in a Lunar Magma Ocean. This analysis does not invalidate the idea of a Lunar Magma Ocean, which seems a necessity under the giant impact hypothesis for the origin of the moon. However, it does indicate that most rocks now seen at the Moonʼs surface are not primary products of a magma ocean alone, but are products of more complex crustal processes.

Reference
Gross J, Treiman AH and Mercer CN (2014) Lunar feldspathic meteorites: Constraints on the geology of the lunar highlands, and the origin of the lunar crust. Earth and Planetary Science Letters 388:318–328.
[doi:10.1016/j.epsl.2013.12.006]
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Ben D. Stanley, Marc M. Hirschmann and Anthony C. Withers

Department of Earth Sciences, University of Minnesota, Minneapolis, MN, 55455, USA

To determine the speciation and concentrations of dissolved C-O-H volatiles in graphite-saturated martian primitive magmas, we conducted piston-cylinder experiments on graphite-encapsulated synthetic melt of Adirondack-class Humphrey basaltic composition. Experiments were performed over three orders of magnitude in oxygen fugacity (IW+2.3 to IW-0.8), and at pressures (1-3.2 GPa) and temperatures (1340-1617 °C) similar to those of possible martian source regions. Oxygen fugacities were determined from compositions of coexisting silicate melt+FePt alloy, olivine+pyroxene+FePt alloy, or melt+Fe-C liquid. Infrared spectra of quenched glasses all show carbonate absorptions at 1430 and 1520 cm^-1, with CO₂ concentrations diminishing under more reduced conditions, from 0.50 wt% down to 26 ppm. Carbon contents of silicate glasses and Fe-C liquids were measured using secondary ion mass spectrometry (SIMS) yielding 36-716 ppm and 6.71-7.03 wt%, respectively. Fourier transform infrared (FTIR) and SIMS analysis produced similar H₂O contents of 0.26-0.85 and 0.29-0.40 wt%, respectively. Raman spectra of glasses reveal evidence for OH^– ions, but no indication of methane-related species. FTIR-measured concentrations of dissolved carbonate diminish linearly with oxygen fugacity, but more reduced conditions yield greater dissolved carbonate concentrations than would be expected based on oxidized conditions in previous work. C contents of silicate glasses determined by SIMS are consistently higher than C as carbonate determined by FTIR. Their difference, termed non-carbonate C, correlates well with additional IR absorptions found in reduced glasses (f_O2<IW+0.4) at 1615, 2205, and 3370 cm^-1. These absorption bands are not seen in more oxidized glasses, except B441 (IW+1.7), presumably because they represent reduced C-bearing complexes. The 2205 cm^-1 peak is attributed to a C=O complex, possibly an Fe-carbonyl ion. The 1615 cm^-1 peak does not correlate with that at 2205 cm^-1, but does correlate with non-carbonate C and is in a region commonly associated with C=O bonding. The origin of the peak at 3370 cm^-1 is poorly understood and could potentially be owing to a variety of C-O-H species or to N-H bonding. The intensities of the 1615 and 3370 cm^-1 peaks correlate with each other leading us to provisionally attribute both to an unspecified complex with both C=O and N-H bonds. These results suggest that dissolved species such as carbonyl or other C=O-bearing species could be a significant source of C fluxes to the martian atmosphere, with minor additions of CO₂ and negligible methane contributions. By assuming that degassed, reduced C ultimately becomes atmospheric CO₂, reduced C outgassing may be incorporated in models of martian atmospheric evolution. At Humphrey source region conditions (1350±50 °C, 1.2±0.1 GPa) the total C contents are equivalent to 1200 ppm CO₂ at IW+1 and 475 ppm CO₂ at IW, which are 2 and 4 times higher than the CO₂ derived from CO₃^2- alone. For reasonable magmatic fluxes over the last 4.5 Ga of martian history, such graphite-saturated magmas would produce 0.25 and 0.60 bars from sources at IW and IW+1, significantly more than expected solely from consideration of dissolved CO₂. The carbon contents of Fe-C liquids in this study are consistent with graphite-saturated carbide liquids becoming more C-rich with increasing temperature. Experiments with melt and Fe-C liquid have values of  between 1.3×10³ and 2.2×10³, potentially allowing planetary mantles to retain significant C following core formation.

Reference
Stanley BD, Hirschmann MM and Withers AC (in press) Solubility of C-O-H volatiles in graphite-saturated martian basalts. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2013.12.013]
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