¹J. Borovička et al. (>10)*
¹Astronomical Institute of the Czech Academy of Sciences, Ondřejov, Czech Republic

The Križevci H6 meteorite was recovered on the basis of fireball data obtained by the cameras of the Croatian Meteor Network. The fireball, which occurred on February 4, 2011, 23:20:40 UT, was also observed by meteor cameras in Slovenia and by the Autonomous Fireball Observatory in Martinsberg, Austria, which belongs to the European Fireball Network. Here, we present detailed data on fireball trajectory, velocity, deceleration, light curve, and orbit. We also modeled the atmospheric fragmentation of the meteoroid on the basis of the light curve and deceleration. The initial mass of the meteoroid was between 25–100 kg, most probably about 50 kg. Severe fragmentation occurred at heights of approximately 60 and 31 km, under dynamic pressures of 0.1 and 3 MPa, respectively. The peak absolute magnitude of −13.7 was reached during the second severe fragmentation event. The recovered 291 g meteorite was probably the only fragment with a terminal mass exceeding 100 g. The orbit had a low inclination of 0.6 degrees, perihelion distance 0.74 AU, and semimajor axis 1.54 AU. Križevci can be ranked among the 10 best documented meteorite falls.

Reference
Borovička J et al. (2015) The instrumentally recorded fall of the Križevci meteorite, Croatia, February 4, 2011. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12469]

Published by arrangement with John Wiley and Sons

^1,2Mutsumi Komatsu, ¹Timothy J. Fagan, ³Takashi Mikouchi, ⁴Michail I. Petaev, ⁵Michael E. Zolensky
¹Department of Earth Sciences, Waseda University, Tokyo, Japan
²Waseda Institute for Advanced Study, Waseda University, Tokyo, Japan
³Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan
⁴Department of Earth and Planetary Sciences, Harvard University and Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USA
⁵NASA Johnson Space Center, Astromaterials Research and Exploration Science (ARES), Houston, Texas, USA

MnO/FeO ratios in olivine from amoeboid olivine aggregates (AOAs) reflect conditions of nebular condensation and can be used in concert with matrix textures to compare metamorphic conditions in carbonaceous chondrites. LIME (low-iron, Mn-enriched) olivine was identified in AOAs from Y-81020 (CO3.05), Kaba (CV~3.1), and in Y-86009 (CV3), Y-86751 (CV3), NWA 1152 (CR/CV3), but was not identified in AOAs from Efremovka (CV3.1–3.4) or Allende (CV>3.6). According to thermodynamic models of nebular condensation, LIME olivine is stable at lower temperatures than Mn-poor olivine and at low oxygen fugacities (dust enrichment <10× solar). Although this set of samples does not represent a single metamorphic sequence, the higher subtypes tend to have AOA olivine with lower Mn/Fe, suggesting that Mn/Fe decreases during parent body metamorphism. Y-81020 has the lowest subtype and most forsteritic AOA olivine (Fo>95) in our study, whereas Efremovka AOAs are slightly Fe-rich (Fo>92). AOA olivines from Kaba are mostly forsteritic, but rare Fe-rich olivine precipitated from an aqueous fluid. A combination of precipitation of Fe-rich olivine and diffusion of Fe into primary olivine grains resulted in iron-rich compositions (Fo97–59) in Allende AOAs. Variations from fine-grained, nonporous matrix toward higher porosity and coarser lath-like matrix olivine can be divided into six stages represented by (1) Y-81020, Efremovka, NWA 1152; (2) Y-86751 lithology B; (3) Y-86009; (4) Kaba; (5) Y-86751 lithology A; (6) Allende. These stages are inferred to represent general degree of metamorphism, although the specific roles of thermally driven grain growth and diffusion versus aqueous dissolution and precipitation remain uncertain.

Reference
Komatsu M, Fagan TJ, Mikouchi T, Petaev MI, Zolensky ME (2015) LIME silicates in amoeboid olivine aggregates in carbonaceous chondrites: Indicator of nebular and asteroidal processes. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12460]

Published by arrangement with John Wiley&Sons

¹Ryuji Okazaki et al. (>10)*
¹Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University, 33, Hakozaki, Higashi-ku 812-8581, Fukuoka, Japan
*Find the extensive, full author and affiliation list on the publishers website

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Reference
Okazaki R et al. (2015) Mineralogy and noble gas isotopes of micrometeorites collected from Antarctic snow. Earth, Planets and Space 2015, 67:90
Link to Article [doi:10.1186/s40623-015-0261-8]

¹Hans-Peter Gail, ¹Stephan Henke, ^2,3Mario Trieloff
¹Institut für Theoretische Astrophysik, Zentrum für Astronomie, Universität Heidelberg, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany
e-mail: gail@uni-heidelberg.de
²Institut für Geowissenschaften, Universität Heidelberg, Im Neuenheimer Feld 236, 69120 Heidelberg, Germany
³Klaus-Tschira-Labor für Kosmochemie, Heidelberg, Im Neuenheimer Feld 236, 69120 Heidelberg, Germany

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Reference
Gail H-P, Henke S, Trieloff M (2015) Thermal evolution and sintering of chondritic planetesimals – II. Improved treatment of the compaction process. Astronomy&Astrophysics 576, A60

Link to Article [http://dx.doi.org/10.1051/0004-6361/201424278]

¹Ernesto Palomba et al. (>10)*
¹INAF-IAPS, Via del Fosso del Cavaliere 100, I-00133 Rome, Italy
*Find the extensive, full author and affiliation list on the publishers website

The discovery of olivine on Vesta’s surface by the VIR imaging spectrometer onboard the Dawn space mission has forced us to reconsider our views of Vestan petrogenetic models. Olivines were expected to be present in the interior of Vesta: in the mantle of a vertically layered body as invoked by the magma ocean models, or at the base (or within) the mantle-crust boundary as proposed by fractionation models. Olivines have been detected by VIR-Dawn in two wide areas near Arruntia and Bellicia, regions located in the northern hemisphere. Interestingly, these olivine-rich terrains are far from the Rheasilvia and the more ancient Veneneia basins, which are expected to have excavated the crust down to reach the mantle. In this work we present our attempts to identify other undetected olivine rich areas on Vesta by using spectral parameters sensitive to olivine such as the Band Area Ratio (BAR) and other specific parameters created for the detection of olivines on Mars (forsterite, fayalite and a generic olivine index). As a preliminary step we calibrated these parameters by means of VIS-IR spectra of different HED meteorite samples: behaviors versus sample grain size and albedo were analyzed and discussed. We selected the BAR and the forsterite index as the best parameters that can be used on Vesta. A cross-correlation analysis has been applied in order to detect olivine signature on the VIR hyperspectral cubes. These detections have then been confirmed by an anti-correlation analysis between the BAR and one of the olivine parameters, independent of the first method applied.
In agreement with the recent discovery, Arruntia and Bellicia were found to be as the most olivine-rich areas, i.e. where the parameter values are strongest. In addition we detected 6 new regions, all but one located in the Vesta north hemisphere. This result confirms again that the old petrogenetic models cannot be straightforwardly applied to Vesta and should be reshaped in the view of these new detections. An alternative and very recent option can be represented by the model according to which surface “eruption” of material from the mantle, including olivine can reach the surface of Vesta.

Reference
Palomba E et al. (2015) Detection of new olivine-rich locations on Vesta. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.06.011]

Copyright Elsevier

¹Wilfred F.M. Röling, ¹Joost W. Aerts, ¹C.H. Lucas Patty, ²Inge Loes ten Kate, ^3,4Pascale Ehrenfreund, ^1,5Susana O.L. Direito
¹Molecular Cell Physiology, Faculty of Earth and Life Sciences, VU University Amsterdam, Amsterdam, the Netherlands.
²Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Utrecht, the Netherlands.
³Space Policy Institute, George Washington University, Washington, DC, USA.
⁴Leiden Observatory, University of Leiden, Leiden, the Netherlands.
⁵School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK.

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Reference
Röling WFM, Aerts JW, Patty CHL, ten Kate IL, Ehrenfreund P, Direito SOL (2015) The Significance of Microbe-Mineral-Biomarker Interactions in the Detection of Life on Mars and Beyond. Astrobiology 15(6): 492-507.
Link to Article [doi:10.1089/ast.2014.1276]

^1,2A. Pommier,³K. Leinenweber, ⁴M. Tasaka
¹University of California San Diego, Scripps Institution of Oceanography, La Jolla, CA 92093, USA
²School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA
³Department of Chemistry & Biochemistry, Arizona State University, Tempe, AZ 85287, USA
⁴Department of Earth Sciences, University of Minnesota, Minneapolis, MN 55455, USA

Electrical conductivity measurements were performed during melting experiments of olivine compacts (dry and hydrous Fo77 and Fo90) at 4 and 6 GPa in order to investigate melt transport properties and quantify the effect of partial melting on electrical properties. Experiments were performed in the multi-anvil apparatus and electrical measurements were conducted using the impedance spectroscopy technique with the two-electrode method. Changes in impedance spectra were used to identify the transition from an electrical response controlled by the solid matrix to an electrical response controlled by the melt phase. This transition occurs slightly above the solidus temperature and lasts until View the MathML sourceTsolidus+75°C (±25). At higher temperature, a significant increase in conductivity (corresponding to an increase in conductivity values by a factor ranging from ∼30 to 100) is observed, consistent with the transition from a tube-dominated network to a structure in which melt films and pools become prominent features. This increase in conductivity corresponds to an abrupt jump for all dry samples and to a smoother increase for the hydrous sample. It is followed by a plateau at higher temperature, suggesting that the electrical response of the investigated samples lacks sensitivity to temperature at an advanced stage of partial melting. Electron microprobe analyses on quenched products indicated an increase in Mg# (molar Mg/(Mg+Fe)Mg/(Mg+Fe)) of olivine during experiments (∼77–93 in the quenched samples with an initial Fo77 composition and ∼92–97 in the quenched samples with an initial Fo90 composition) due to the partitioning of iron to the melt phase. Assuming a respective melt fraction of 0.10 and 0.20 before and after the phase of significant increase in conductivity, in agreement with previous electrical and permeability studies, our results can be reproduced satisfactorily by two-phase electrical models (the Hashin and Shtrikman bounds and the modified brick layer model), and provide a melt conductivity value of 78 (±8) S/m for all Fo77 samples and 45 (±5) S/m for the Fo90 sample. Comparison of our results with electromagnetic sounding data of the deep interior of the Moon supports the hypothesis of the presence of interconnected melt at the base of the lunar mantle. Our results underline that electrical conductivity can be used to investigate in situ melt nucleation and migration in the interior of terrestrial planets.

Reference
Pommier A, Leinenweber K, Tasaka M (2015) Experimental investigation of the electrical behavior of olivine during partial melting under pressure and application to the lunar mantle. Earth and Planetary Science Letters (in Press)
Link to Article [doi:10.1016/j.epsl.2015.05.052]

Copyright Elsevier

¹Dwijesh Ray, ¹S. Ghosh, ¹S.V.S. Murty
¹PLANEX, Physical Research Laboratory, Ahmedabad 380009, India

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Ray D, Ghosh D, Murty SVS (2015) Shock-Thermal History of Kavarpura IVA Iron: Evidences from Microtextures and Nickel Profiling. Planetary and Space Science (in Press)
Link to Article [doi:10.1016/j.pss.2015.05.016]

¹David M.H. Baker, ¹James W. Head
¹Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912

Important to understanding the process of basin formation on planetary bodies are constraints on the mineralogy and depths of origin of interior ring structures. We summarize previous analyses of the mineralogy of basin materials on the Moon and use hyperspectral image-cubes from the Chandrayaan-1’s Moon Mineralogy Mapper (M3) to determine the mineralogy of interior rings in lunar protobasins and peak-ring basins. Nearly all peak rings outside of South Pole-Aitken (SPA) basin have extensive outcrops of pure anorthosite (⩾99% plagioclase) on the order of several square kilometers in areal dimensions. No obvious mantle components were identified. Outcrops spectrally dominated by pyroxene occur within SPA and other areas of thinner crust, such as regions within large ancient impact basins. In addition, many outcrops of candidate shocked plagioclase are observed within the same peak rings containing crystalline plagioclase. These spectral observations strongly support a crustal origin for peak rings on the Moon. Recent analyses of the Orientale basin and other lunar basins show that the inner rings of multi-ring basins are also anorthosite-rich and therefore derived from the lunar crust. To further constrain the depths of origin of materials forming peak rings, we compare the pre-impact crustal thickness for each basin with calculated vertical reference points, including: 1) maximum depth of excavation, which is the deepest point at which the crater will excavate material, 2) maximum depth of melting, which is deeper than the maximum depth of excavation and represents the maximum extent of impact-induced melting beneath the sub-impact point, and 3) maximum depth of the transient cavity, which is deepest part of the growing transient cavity that is formed of both excavated and displaced target material. Taken together with the observed mineralogy, the origin of peak-ring lithologies is constrained to stratigraphic levels near the maximum depth of excavation and likely shallower than this if the lower crust is comprised of noritic materials. The maximum depth of melting for peak-ring basins extends far into the mantle and is therefore not a valid proxy for estimating the depth of origin of materials forming peak rings. We find that our estimates of the depths of origin of peak-ring materials are consistent with current models of peak-ring formation, including predictions by hydrocode simulations and conceptual models emphasizing the role of interior impact melting and centro-symmetric collapse of the walls of the transient cavity. Firmer constraints on the depths of origin of peak rings on the Moon await an improved understanding of the crustal compositional structure, particularly that of the lower crust, and improved model predictions on the sampling depths and shock pressures experienced by uplifted peak-ring materials.

Reference
Baker DMH, Head JW (2015) Constraints on the Depths of Origin of Peak Rings on the Moon from Moon Mineralogy Mapper Data. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.06.013]

Copyright Elsevier

¹Charles Galdies
¹Institute of Earth Systems, University of Malta, Msida, MSD 2080, Malta

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Reference
Galdies C (2015) A Spectral and Morphometric Analysis of a Small Lunar Dome Complex Blanketed by Ejecta in Euclides-J Region. Earth, Moon, and Planets (in Press)
Link to Article [DOI 10.1007/s11038-015-9472-z]