¹Lidia Pittarello et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.04.033]
¹Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
Copyright Elsevier

Melting experiments attempting to reproduce some of the processes affecting asteroidal and cometary material during atmospheric entry have been performed in a high enthalpy facility. For the first time with the proposed experimental setup, the resulting material has been recovered, studied, and compared with natural analogues, focusing on the thermal and redox reactions triggered by interaction between the melt and the atmospheric gases under high temperature and low pressure conditions. Experimental conditions were tested across a range of parameters, such as heat flux, experiment duration, and pressure, using two types of sample holders materials, namely cork and graphite. A basalt served as asteroidal analog and to calibrate the experiments, before melting a H5 ordinary chondrite meteorite. The quenched melt recovered after the experiments has been analyzed by μ-XRF, EDS-SEM, EMPA, LA-ICP-MS, and XANES spectroscopy.
The glass formed from the basalt is fairly homogeneous, depleted in highly volatile elements (e.g., Na, K), relatively enriched in moderately siderophile elements (e.g., Co, Ni), and has reached an equilibrium redox state with a lower Fe3+/Fetot ratio than that in the starting material. Spherical objects, enriched in SiO2, Na2O and K2O, concentrations, were observed, inferring condensation from the vaporized material. Despite instantaneous quenching, the melt formed from the ordinary chondrite shows extensive crystallization of mostly olivine and magnetite, the latter indicative of oxygen fugacity compatible with presence of both Fe2+ and Fe3+. Similar features have been observed in natural meteorite fusion crusts and in micrometeorites, implying that, at least in terms of maximum temperature reached and chemical reactions, the experiments have successfully reproduced the conditions likely encountered by extraterrestrial material following atmospheric entry.

¹Charity M.Phillips-Lander,¹Andrew S.Elwood Madden,²Elisabeth M.Hausrath,¹Megan Elwood Madden
Geochimica et Cosmochimcia Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.05.006]
¹School of Geology and Geophysics, University of Oklahoma, 100 E. Boyd Street, Norman, OK 73069, USA
²Department of Geoscience, University of Nevada, Las Vegas 4505 S. Maryland Ave., Las Vegas, NV 89154
Copyright Elsevier

Both high and low calcium pyroxene minerals have been detected over large portions of the martian surface in addition to widespread salts in martian soils and dust. Calcium pyroxenes in martian meteorites are associated with secondary evaporite phases, including sulfates, chlorides, and perchlorates, suggesting the pyroxene may have been altered in saline solutions. Therefore, understanding pyroxene mineral weathering in high salinity brines may provide insight into past aqueous alteration on Mars. This study examines both solute-based dissolution rates and qualitative assessments of weathering textures developed during pyroxene-brine alteration experiments to link dissolution rates and textures and aid in interpreting weathering features observed in Mars meteorites and future pyroxene samples returned from Mars. Batch reactor dissolution experiments were conducted at 298 K to compare diopside (a high Ca-pyroxene) dissolution rates in water (18 MΩcm-1 ultrapure water (UPW); activity of water (ɑH2O) =1.0), 0.35 mol kg-1 NaCl (ɑH2O =0.99), 0.35 mol kg-1 Na2SO4 (ɑH2O =0.98), 2 mol kg-1 NaClO4 (ɑH2O =0.90), 2.5 mol kg-1 Na2SO4 (ɑH2O =0.95), 5.7 mol kg-1 NaCl (ɑH2O =0.75), and 9 mol kg-1 CaCl2 (ɑH2O =0.35) brines at pH 5-6.6 to determine how changing solution chemistry and activity of water influence pyroxene dissolution. Aqueous Si release rates and qualitative textural analyses indicate diopside dissolution rates are influenced by both solution chemistry and activity of water, with diopside weathering increasing along a trend from: 9 mol kg-1 CaCl2 < UPW (-9.82± 0.03 log mol m-2 s-1) ≈ 2 mol kg-1 NaClO4 ≈ 0.35 mol kg-1 Na2SO4 (-9.80± 0.07) ≈ 5.7 mol kg-1 NaCl (-9.69 ± 0.04) < 0.35 mol kg-1 NaCl (-9.45± 0.34) < 2.5 mol kg-1 Na2SO4 (-8.99± 0.09). Dissolution rates increase in sodium sulfate brines with increasing salinity. In contrast, Si-based dissolution rates in 0.35 mol kg-1 NaCl are faster than those measured in 5.7 mol kg-1 NaCl and UPW. However, all of the Si-based rates measured in the chloride and sulfate salt solutions are likely affected by precipitation of Si-rich secondary clay minerals, which removed Si from solution. Qualitative textural analyses indicate similar degrees of dissolution occurred in UPW and 2 M NaClO4; however, no aqueous rate determinations could be made in perchlorate brines due to explosion hazards. Aqueous Si was below detection limits in the 9 mol kg-1 CaCl2 experiments, but textural analysis suggests limited diopside dissolution occurred. Therefore, despite low water activity, diopside dissolution proceeds in both dilute to high salinity brines, readily forming clay minerals under a wide range of conditions. This suggests that outcrops on Mars containing pyroxene preserved with sulfate, chloride, perchlorate, and/or clay minerals likely record relatively short periods (<1 million years) of aqueous alteration. Si-rich spherules similar to those observed in SNC meteorites were also observed in the 5.7 mol kg-1 NaCl brine experiments, indicating that silicate mineral alteration in chloride brines may lead to Si-rich alteration products and coatings.

^1,2Milligan, J.N.,¹Royer, D.L.,³Franks, P.J.,⁴Upchurch, G.R.,¹McKee, M.L.
Geophysical Research Letters 46, 3462-3472 Link to Article [DOI: 10.1029/2018GL081215]
¹Department of Earth and Environmental Sciences, Wesleyan University, Middletown, CT, United States
²Department of Geology, Baylor University, Waco, TX, United States
³School of Life and Environmental Sciences, University of Sydney, Sydney, NSW, Australia
⁴Department of Biology, Texas State University, San Marcos, TX, United States

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¹Petrova, E.V.,¹Maksimova, A.A.,¹Chukin, A.V.,¹Oshtrakh, M.I.
Hyperfine Interactions 240, 42 Link to Article [DOI: 10.1007/s10751-019-1592-9]
¹Department of Experimental Physics, Institute of Physics and Technology, Ural Federal University, Ekaterinburg, 620002, Russian Federation

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¹Yoko Kebukawa,²Conel M. O’D. Alexander,¹George D. Cody
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13302]
¹Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, Washington, District of Columbia, 20015 USA
²Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, Washington, District of Columbia, 20015 USA
Published by arrangement with John Wiley & Sons

Past studies of the various separable carbonaceous fractions have been unable to account for all of C in primitive chondrites. In particular, up to 20–50% of the C is lost during acid leaching of bulk samples even after the C in carbonates and soluble organic matter is accounted for. To try to better characterize the nature of this “missing C,” we have compared the bulk infrared (IR) absorption spectra of a number of primitive chondrites with those of their previously reported insoluble organic matter (IOM). The aliphatic C–H stretching bands, in particular, allow us to compare the molecular structures of bulk C with that of IOM. The spectral differences between bulk C and IOM reflect “missing C” phases that were lost during acid leaching, although we cannot completely exclude the possibility that the OM was modified after demineralization. Comparing IR spectra of bulk meteorite powder and IOM suggests that the missing C varies in its molecular structure, and that mildly thermally metamorphosed type 3 chondrites tend to be richer in an aliphatic fraction with lower CH₂/CH₃ ratios, relative to IOM, compared to aqueously altered carbonaceous chondrites (CI/CM/CR). The missing C is most likely released from acid‐labile functional groups, such as esters, acetals, and amides, during demineralization, although it cannot be ruled out that some fraction of the missing C is in small grains that are difficult to recover from suspension, or in water‐soluble compounds trapped in phyllosilicates.

¹Anthony Gargano,²Zachary Sharp
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13303]
¹Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, 87131‐0001 USA
²Center for Stable Isotopes, University of New Mexico, Albuquerque, New Mexico, 87131‐0001 USA
Published by arrangement with John Wiley & Sons

The bulk chlorine concentrations and isotopic compositions of a suite of non‐carbonaceous (NC) and carbonaceous (CC) iron meteorites were measured using gas source mass spectrometry. The δ37Cl values of magmatic irons range from −7.2 to 18.0‰ versus standard mean ocean chloride and are unrelated to their chlorine concentrations, which range from 0.3 to 161 ppm. Nonmagmatic IAB irons are comparatively Cl‐rich containing >161 ppm with δ37Cl values ranging from −6.1 to −3.2‰. The anomalously high and low δ37Cl values are inconsistent with a terrestrial source, and as Cl contents in magmatic irons are largely consistent with derivation from a chondrite‐like silicate complement, we suggest that Cl is indigenous to iron meteorites. Two NC irons, Cape York and Gibeon, have high cooling rates with anomalously high δ37Cl values of 13.4 and 18.0‰. We interpret these high isotopic compositions to result from Cl degassing during the disruption of their parent bodies, consistent with their low volatile contents (Ga, Ge, Ag). As no relevant mechanisms in iron meteorite parent bodies are expected to decrease δ37Cl values, whereas volatilization is known to increase δ37Cl values by the preferential loss of light isotopes, we interpret the low isotope values of <−5‰ and down to −7.2‰ to most closely represent the primordial isotopic composition of Cl in the solar nebula. Similar conclusions have been derived from low δ37Cl values down to −6, and −3.8‰ measured in Martian and Vestan meteorites, respectively. These low δ37Cl values are in contrast to those of chondrites which average around 0‰ previously explained by the incorporation of isotopically heavy HCl clathrate into chondrite parent bodies. The poor retention of low δ37Cl values in many differentiated planetary materials suggest that extensive devolatilization occurred during planet formation, which can explain Earth’s high δ37Cl value by the loss of approximately 60% of the initial Cl content.

^1,2Mike Meyer,³Peter J. Harries,⁴Roger W. Portell
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13299]
¹Earth and Environmental Science Department, Harrisburg University, Harrisburg, Pennsylvania, 17101 USA
²Geophysical Laboratory, Carnegie Institution for Science, Washington, DC, 20005 USA
³Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina, 27695 USA
⁴Florida Museum of Natural History, University of Florida, Gainesville, Florida, 32611 USA
Published by arrangement with John Wiley & Sons

The Plio‐Pleistocene Upper Tamiami Formation (Pinecrest beds) of Florida is well known for its fossiliferous shell beds, but not for its extraterrestrial material. Here we report the first occurrence of tiny (~200 μm in diameter) silica‐rich microspherules from this unit and from the state. This material was analyzed using petrographic and elemental methods using energy dispersive X‐ray spectroscopy (EDS). The majority of microspherules are glassy and translucent in reflected light with some displaying “contact pairs” (equal‐sized micro‐spherules attached to each other). Broken microspherules cleave conchoidally, often with small internal spherical vesicles, but most lack any other evidence of internal features, such as layering. Using the EDS data, the microspherules were compared to volcanic rocks, microtektites, and cosmic spherules (micrometeorites). Based on their physical characteristics and elemental compositions these are likely microtektites or a closely related type of material. The high Na content in the examined material deviates significantly from the abundances usually found in micrometeorites and tektite material; this is enigmatic and requires further study. This material may be derived from a nearby previously unknown impact event; however, more material and sites are required to confirm the source of this material. Because of the focus on molluscan fossils in southwestern Florida shell beds, microtektite material has likely been overlooked in the past, and it is probable that these microspherules are in abundance elsewhere in these units and possibly throughout the region.

^1,2Nichols, C.I.O.,^1,3Einsle, J.F.,^4,5,6Im, M.-Y.,⁷Kasama, T.,^3,8Saghi, Z.,³Midgley, P.A.,¹Harrison, R.J.
Geochemistry, Geophysics, Geosystems 20, 1441-1453 Link to Article [DOI: 10.1029/2018GC008159]
¹Department of Earth Sciences, University of Cambridge, Cambridge, United Kingdom
²Department of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA, United States
³Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, United Kingdom
⁴Center for X-ray Optics, Lawrence Berkeley National Laboratory, Berkeley, CA, United States
⁵Department of Emerging Materials Science, DGIST, Daegu, South Korea
⁶School of Materials Science and Engineering, Ulsan National Institute of Science and Technology, Ulsan, South Korea
⁷National Centre for Nano Fabrication and Characterisation, Technical University of Denmark, Kongens Lyngby, Denmark
⁸CEA, LETI, MINATEC Campus, Grenoble, France

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¹Hayashi, T.,¹Muramatsu, H.,¹Maehisa, K.,¹Yamasaki, N.Y.,¹Mitsuda, K.,²Maehata, K.,³Hara, T.
IEEE Transactions on Applied Superconductivity 29, #8654629 Link to Article [DOI: 10.1109/TASC.2019.2902304]
¹Institute of Space and Astronautical Science Japan Aerospace Exploration Agency (ISAS/JAXA), Kanagawa, 252-5210, Japan
²Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Fukuoka, 819-0395, Japan
³National Institute for Materials Science (NIMS), Ibarakiken, 305-0044, Japan

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^1,2Miyahara, M.,²Ohtani, E.,³Nishijima, M.,⁴El Goresy, A.
Physics of the Earth and Planetary Interiors 291, 1-11 Link to Article [DOI: 10.1016/j.pepi.2019.04.001]
¹Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, 739-8526, Japan
²Department of Earth Sciences, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan
³Institute for Materials Research, Tohoku University, Sendai, 980-8577, Japan
⁴Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth, D-95440, Germany

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