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.

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

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

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

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

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

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]

^1,2,3Birger Schmitz, ¹Samuele Boschi, ¹Anders Cronholm, ^2,4Philipp R. Heck, ⁵Simonetta Monechi, ⁶Alessandro Montanari, ¹Fredrik Terfelt
¹Astrogeobiology Laboratory, Department of Physics, Lund University, Sweden
²Robert A. Pritzker Center for Meteoritics and Polar Studies, The Field Museum of Natural History, Chicago, IL, USA
³Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Manoa, Honolulu, HI, USA
⁴Chicago Center for Cosmochemistry, The University of Chicago, Chicago, IL, USA
⁵Department of Earth Sciences, Florence University, Florence, Italy
⁶Geological Observatory of Coldigioco, Frontale di Apiro, Macerata, Italy

The onset of Earth’s present icehouse climate in the Late Eocene coincides with astronomical events of enigmatic causation. At ∼36 Ma ago the 90–100 km large Popigai and Chesapeake Bay impact structures formed within ∼10–20 ka∼10–20 ka. Enrichments of 3He in coeval sediments also indicate high fluxes of interplanetary dust to Earth for ∼2 Ma∼2 Ma. Additionally, several medium-sized impact structures are known from the Late Eocene. Here we report from sediments in Italy the presence of abundant ordinary chondritic chromite grains (63–250 μm) associated with the ejecta from the Popigai impactor. The grains occur in the ∼40 cm∼40 cm interval immediately above the ejecta layer. Element analyses show that grains in the lower half of this interval have an apparent H-chondritic composition, whereas grains in the upper half are of L-chondritic origin. The grains most likely originate from the regoliths of the Popigai and the Chesapeake Bay impactors, respectively. These asteroids may have approached Earth at comparatively low speeds, and regolith was shed off from their surfaces after they passed the Roche limit. The regolith grains then settled on Earth some 100 to 1000 yrs after the respective impacts. Further neon and oxygen isotopic analyses of the grains can be used to test this hypothesis.
If the Popigai and Chesapeake Bay impactors represent two different types of asteroids one can rule out previous explanations of the Late Eocene extraterrestrial signatures invoking an asteroid shower from a single parent-body breakup. Instead a multi-type asteroid shower may have been triggered by changes of planetary orbital elements. This could have happened due to chaos-related transitions in motions of the inner planets or through the interplay of chaos between the outer and inner planets. Asteroids in a region of the asteroid belt where many ordinary chondritic bodies reside, were rapidly perturbed into orbital resonances. This led to an increase in small to medium-sized collisional breakup events over a 2–5 Ma period. This would explain the simultaneous delivery of excess dust and asteroids to the inner solar system. Independent evidence for our scenario are the common cosmic-ray exposure ages in the range of ca. 33–40 Ma for recently fallen H and L chondrites.
The temporal coincidence of gravity disturbances in the asteroid belt with the termination of ice-free conditions on Earth after 250 Ma is compelling. We speculate that this coincidence and a general correlation during the past 2 Ga between K–Ar breakup ages of parent bodies of the ordinary chondrites and ice ages on Earth suggest that there may exist an astronomical process that disturbs both regions of the inner asteroid belt and Earth’s orbit with a potential impact on Earth’s climate.

Reference
Schmitz B, Boschi S, Cronholm A, Heck PR, Monechi S, Montanari A, Terfelt F (2015) Fragments of Late Eocene Earth-impacting asteroids linked to disturbance of asteroid belt. Earth and Planetary Science Letters 425, 77–83.
Link to Article [doi:10.1016/j.epsl.2015.05.041]

Copyright Elsevier

¹Yang Chen, ¹Yang Liu, ²Yunbin Guan, ²John M. Eiler, ²Chi Ma, ²George R. Rossman, ³Lawrence A. Taylor
¹Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
²Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
³Planetary Geosciences Institute, Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996, USA

We report unambiguous chemical evidence for subsurface water activity in the martian crust at <600 Ma based on the data from Tissint, a fresh martian meteorite fall with minimal terrestrial weathering. The impact-melt pockets in Tissint contain abundant volatiles (H₂O, CO₂, F, and Cl), and their concentrations are positively correlated with each other. Higher H₂O concentrations also accompany higher deuterium contents. These correlations suggest mixing between two volatile sources. The first source is H₂O in the precursor basalt inherited from martian magma. Magmatic H₂O in the basalt had low deuterium concentration and was likely stored in the nominally anhydrous minerals. This source contributed little CO₂ or halogens to the impact melts. The second source is inferred to be aqueous-alteration products introduced to the basalt by water activity after the basalt erupted. These alteration materials contributed more volatiles to the impact melts than the magmatic source, and had high deuterium abundance, reflecting isotope equilibrium with recent martian atmosphere. The water activities occurred beneath the martian surface after ∼600 Ma (crystallization age), but before ∼1 Ma (ejection age). The chemical and isotopic signatures of the alteration products in Tissint resemble previously known martian samples associated with old water activities on Mars, which can be traced back to ∼4.2 billion years ago (e.g., the mudstone at Gale Crater). This similarity in chemistry and the wide age-span indicate that such water activities were common on Mars throughout its history, which had the potential to form habitable environment. However, the rarity of the volatile-rich zone in Tissint suggests that Martian crustal aqueous processes, where they have occurred are generally limited in their extent of water–rock reaction.

Reference
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]

Copyright Elsevier

¹Kevin M. Cannon, ¹John F. Mustard
¹Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, Rhode Island 02912, USA

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

Reference
Cannon KM, Mustard JF (2015) Preserved glass-rich impactites on Mars. Geology (in Press)
Link to Article [10.1130/G36953.1]

¹Mai Yia Xiong, ¹Evgenya S. Shelobolina, ¹Eric E. Roden
¹Department of Geoscience, University of Wisconsin, and NASA Astrobiology Institute, University of Wisconsin, Madison, Wisconsin.

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

Reference
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]

¹G. J. Wasserburg, ²O. Trippella, ³M. Busso
¹Lunatic Asylum, Geological & Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
²Department of Physics & Geology, University of Perugia, and INFN, Section of Perugia, via A. Pascoli, Perugia, I-06123, Italy

We study the effects of neutron captures in AGB stars on “Fe-group” elements, with an emphasis on Cr, Fe, and Ni. These elements show anomalies in 54Cr, 58Fe, and 64Ni in solar system materials, which are commonly attributed to supernovae (SNe). However, as large fractions of the interstellar medium (ISM) were reprocessed in AGB stars, these elements were reprocessed, too. We calculate the effects of such reprocessing on Cr, Fe, and Ni through 1.5 ${{M}_{\odot }}$ and 3 ${{M}_{\odot }}$ AGB models, adopting solar and 1/3 solar metallicities. All cases produce excesses of 54Cr, 58Fe, and 64Ni, while the other isotopes are little altered; hence, the observations may be explained by AGB processing. The results are robust and not dependent on the detailed initial isotopic composition. Consequences for other “Fe group” elements are then explored. They include 50Ti excesses and some production of $^{46,47,49}$Ti. In many circumstellar condensates, Ti quantitatively reflects these effects of AGB neutron captures. Scatter in the data results from small variations (granularity) in the isotopic composition of the local ISM. For Si, the main effects are instead due to variations in the local ISM from different SN sources. The problem of Ca is discussed, particularly with regard to 48Ca. The measured data are usually represented assuming terrestrial values for 42Ca/44Ca. Materials processed in AGB stars or sources with variable initial 42Ca/44Ca ratios can give apparent 48Ca excesses/deficiencies, attributed to SNe. The broader issue of galactic chemical evolution is also discussed in view of the isotopic granularity in the ISM.

Reference
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]