Multiwall and bamboo-like carbon nanotubes from the Allende chondrite: A probable source of asymmetry

1Cruz-Rosas, H.I.,2Riquelme, F.,3Santiago, P.,3Rendón, L.,4Buhse, T.,5Ortega-Gutiérrez, F.,6Borja-Urby, R.,7Mendoza, D.,1Gaona, C.,1Miramontes, P.,3Cocho, G.
PLoS ONE 14, e0218750 Link to Article [DOI: 10.1371/journal.pone.0218750]
1Facultad de Ciencias, Universidad Nacional Autónoma de México, Ciudad Universitaria, Cd. Mx., Mexico
2Laboratorio de Sistemática Molecular, Escuela de Estudios Superiores del Jicarero, Universidad Autónoma del Estado de Morelos, Jicarero, Morelos, Mexico
3Instituto de Física, Universidad Nacional Autónoma de México, Ciudad Universitaria, Cd. Mx., Mexico
4Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Cuernavaca, Morelos, Mexico
5Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Cd. Mx., Mexico
6Centro de Nanociencias y Micro y Nanotecnologías, Instituto Politécnico Nacional, Zacatenco, Cd. Mx., Mexico
7Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Ciudad Universitaria, Cd. Mx., Mexico

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New applications of high-resolution analytical methods to study trace organic compounds in extraterrestrial materials

1,2Naraoka, H.,1Hashiguchi, M.,3Sato, Y.,1,3Hamase, K.
Life 9, 62 Link to Article [DOI: 10.3390/life9030062]
1Research Center for Planetary Trace Organic Compounds, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan
2Department of Earth and Planetary Sciences, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan
3Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan

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Origin and abundances of H2O in the terrestrial planets, Moon, and asteroids

1Francis M.McCubbin,1,2Jessica J.Barnes
Earth and Planetary Science Letters 526, 115771 Link to Article [https://doi.org/10.1016/j.epsl.2019.115771]
1Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, 2101 NASA Parkway, Houston, TX 77058, United States
2Lunar and Planetary Laboratory, University of Arizona, 1629 E University Blvd, Tucson, AZ 85721, United States
Copyright Elsevier

The presence of H2O within differentiated terrestrial bodies in the inner Solar System is well established; however, the source(s) of this H2O and the time of its arrival to the inner Solar System is an area of active study. At present, the prevailing model for the origin of inner Solar System H2O calls upon carbonaceous chondrites as the source. This is largely based on reported observations that H- and N-isotopic compositions of differentiated planetary bodies are largely the same and within a range of values that overlaps with carbonaceous chondrites as opposed to comets or the Sun. In this contribution, we evaluate the efficacy of this model and other models for the origin of inner Solar System H2O by considering geochronological constraints on early Solar System history, constraints on primary building blocks of differentiated bodies based on nucleosynthetic isotope anomalies, and constraints from dynamical models of planet formation. In addition to H- and N-isotopic data, these constraints indicate that an interstellar source of H2O was present in the inner Solar System within the first 4 Ma of CAI formation. Furthermore, the most H2O-rich carbonaceous chondrites are unlikely to be the source of H2O for the earliest-formed differentiated bodies based on their minimally overlapping primary accretion windows and the separation of their respective isotopic reservoirs by Jupiter in the timespan of about 1–4 Ma after CAI formation. The presence of deuterium-rich, non-nebular H2O sources in the inner Solar System prior to the formation of carbonaceous chondrites or comets implies early contributions of interstellar ices to both the inner and outer Solar System portions of the protoplanetary disk. Evidence for this interstellar ice component in the inner Solar System may be preserved in LL chondrites and in the mantle of Mars. In contrast to the earlier-formed bodies within the inner Solar System, Earth’s protracted accretion window may have facilitated incorporation of H2O in its interior from both the inner and outer Solar System, helping the Earth to become a habitable planet.

U, Th, and K partitioning between metal, silicate, and sulfide and implications for Mercury’s structure, volatile content, and radioactive heat production

1,2Asmaa Boujibar,3,4,5Mya Habermann,1Kevin Righter,6,7D. Kent Ross,6Kellye Pando,8Minako Righter,9Bethany A. Chidester,6Lisa R. Danielson
American Mineralogist 104, 1221-1237 Link to Article [https://doi.org/10.2138/am-2019-7000]
1NASA Johnson Space Center, 2101 E NASA Parkway, Houston, Texas 77058, U.S.A.
2Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington, D.C. 20015, U.S.A.
3Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, Texas 77058, U.S.A.
4HX5, NASA Johnson Space Center, 2101 E NASA Parkway, Houston, Texas 77058, U.S.A.
5Department of Earth and Planetary Sciences, University of New Mexico, 221 Yale Boulevard NE, Albuquerque, New Mexico 87131, U.S.A.
6Jacobs, NASA Johnson Space Center, 2101 E NASA Parkway, Houston, Texas 77058, U.S.A.
7UTEP-CASSMAR, 500 W University Avenue, El Paso, Texas 79968, U.S.A.
8Department of Earth and Atmospheric Sciences, University of Houston, 3507 Cullen Boulevard, Houston, Texas 77004, U.S.A.
9Department of the Geophysical Sciences, University of Chicago, 5734 S Ellis Avenue, Chicago, Illinois 60637, U.S.A.
Copyright: The Mineralogical Society of America

The distribution of heat-producing elements (HPE) potassium (K), uranium (U), and thorium (Th) within planetary interiors has major implications for the thermal evolution of the terrestrial planets and for the inventory of volatile elements in the inner solar system. To investigate the abundances of HPE in Mercury’s interior, we conducted experiments at high pressure and temperature (up to 5 GPa and 1900 °C) and reduced conditions (IW-1.8 to IW-6.5) to determine U, Th, and K partitioning between metal, silicate, and sulfide (Dmet/sil and Dsulf/sil). Our experimental data combined with those from the literature show that partitioning into sulfide is more efficient than into metal and that partitioning is enhanced with decreasing FeO and increasing O contents of the silicate and sulfide melts, respectively. Also, at low oxygen fugacity (log fO2 < IW-5), U and Th are more efficiently partitioned into liquid iron metal and sulfide than K. Dmet/sil for U, Th, and K increases with decreasing oxygen fugacity, while Dmet/silUDUmet/sil and Dmet/silKDKmet/sil increase when the metal is enriched and depleted in O or Si, respectively. We also used available data from the literature to constrain the concentrations of light elements (Si, S, O, and C) in Fe metal and sulfide. We calculated chemical compositions of Mercury’s core after core segregation, for a range of fO2 conditions during its differentiation. For example, if Mercury differentiated at IW-5.5, its core would contain 49 wt% Si, 0.02 wt% S, and negligible C. Also if core-mantle separation happened at a fO2 lower than IW-4, the bulk Mercury Fe/Si ratio is likely to be chondritic. We calculated concentrations of U, Th, and K in the Fe-rich core and possible sulfide layer of Mercury. Bulk Mercury K/U and K/Th were calculated taking all U, Th, and K reservoirs into account. Without any sulfide layer, or if Mercury’s core segregated at a higher fO2 than IW-4, bulk K/U and K/Th would be similar to those measured on the surface, confirming more elevated volatile K concentration than previously expected for Mercury. However, Mercury could fall on an overall volatile depletion trend where K/U increases with the heliocentric distance if core segregation occurred near IW-5.5 or more reduced conditions, and with a sulfide layer of at least 130 km thickness. At these conditions, the bulk Mercury K/Th ratio is close to Venus’s and Earth’s values. Since U and Th become more chalcophile with decreasing oxygen fugacity, to a higher extent than K, it is likely that at an fO2 close to, or lower than, IW-6 both K/U and K/Th become lower than values of the other terrestrial planets. Therefore, our results suggest that the elevated K/U and K/Th ratios of Mercury’s surface should not be exclusively interpreted as the result of a volatile enrichment in Mercury, but could also indicate a sequestration of more U and Th than K in a hidden iron sulfide reservoir, possibly a layer present between the mantle and core. Hence, Mercury could be more depleted in volatiles than Mars with a K concentration similar to or lower than the Earth’s and Venus’s, suggesting volatile depletion in the inner solar system. In addition, we show that the presence of a sulfide layer formed between IW-4 and IW-5.5 decreases the total radioactive heat production of Mercury by up to 30%.

Modal abundances of coarse-grained (>5 μm) components within CI-chondrites and their individual clasts – Mixing of various lithologies on the CI parent body(ies)

1,2Julian Alfing,1Markus Patzek,1Addi Bischoff
Geochemistry (Chemie der Erde) Link top Article [https://doi.org/10.1016/j.chemer.2019.08.004]
1Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm Str. 10, D-48149, Münster, Germany
2Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Corrensstr. 24, D-48149, Münster, Germany
Copyright Elsevier

For the bulk rocks of CI chondrites, various values are given for the modal abundance of matrix (95–100 vol%) and the accompanying mineral constituents. Here, we have determined the modal abundance of phases >5 μm in the CI chondrites Orgueil, Ivuna, Alais, and Tonk. Considering this cut-off grain-size to distinguish between matrix and coarse-grained constituents, then, we find the modal abundance of the minor phases magnetite, pyrrhotite, carbonate, olivine, and pyroxene to be 6 vol% in total, and these phases are embedded within the fine-grained, phyllosilicate-rich matrix, making up 94 vol%. The values vary slightly from meteorite to meteorite. Considering all four chondrites, the most abundant phase is – by far – magnetite (4.3 vol%) followed by pyrrhotite (∼1.1 vol%). All four CI chondrites are complex breccias, and their degree of brecciation decreases in the sequence: Orgueil > Ivuna > Alais ∼ Tonk. Because these meteorites contain clasts with highly variable modal abundances, we therefore also studied individual clasts with high abundances of specific coarse-grained phases. In this respect, in Orgueil we found a fragment with a 21.5 vol% of magnetite as well as a clast having 31.8 vol% phosphate. In Ivuna, we detected an individual clast with a 21.5 vol% of carbonates. Thus, since the CI composition is used as a geochemical standard for comparison, one also should keep in mind that sufficiently large sample masses are required to reveal a homogeneous CI composition. Small aliquots with one dominating lithology may significantly deviate from the suggested standard CI composition.

Fine-grained rim formation – high speed, kinetic dust aggregation in the early Solar System

1Kurt Liffman
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.08.009]
1Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia
Copyright Elsevier

Type 3 chondritic meteorites often contain chondrules and refractory inclusions that are coated with accretionary, fine-grained rims (FGRs). FGRs are of low porosity, were subject to centrally directed pressure, may contain high temperature products like microchondrules and there is a linear relationship between the rim thickness and the radius of the enclosed object.

FGRs are thought to have formed by the gentle adhesion of dust onto the central object with the subsequent compression of this fluffy rim within the parent body. However, this model does not explain the low porosity, micro-chondrules and centralized pressure. This model also has difficulties explaining the linear relationship between rim thickness and object size including the existence of a non-zero constant in that linear relationship.

We propose that FGRs formed by the relatively high-speed interaction between dust and the object, where high initial impact speed produced abrasion and, possibly, microchondrules. FGR formation occurred over a range of lower speeds aided by vacuum adhesion of fragments from the impacting dust particles. This model naturally produces the rim thickness linear relationship with non-zero constant, low porosity and centrally directed pressure. We call this process kinetic dust aggregation (KDA), which is another name for the aerosol deposition processes used in industry. KDA may be a tentative, part explanation of how dust aggregation occurs in protostellar disks on the pathway from dust to planets.

Evidence for subsolidus quartz-coesite transformation in impact ejecta from the Australasian tektite strewn field

1,2Fabrizio Campanale,2Enrico Mugnaioli,1 Luigi Folco,2Mauro Gemmi,3Martin R.Lee,3Luke Daly,4Billy P.Glass
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.08.014]
1Dipartimento di Scienze della Terra, Università di Pisa, V. S. Maria 53, 56126 Pisa, Italy
2Center for Nanotechnology Innovation@NEST, Istituto Italiano di Tecnologia (IIT), Piazza San Silvestro 12, 56127 Pisa, Italy
3Department of Geographical and Earth Sciences, University of Glasgow, Glasgow G12 8QQ, UK
4Department of Geosciences, University of Delaware, Newark, DE, USA
Copyright Elsevier

Coesite, a high-pressure silica polymorph, is a diagnostic indicator of impact cratering in quartz-bearing target rocks. The formation mechanism of coesite during hypervelocity impacts has been debated since its discovery in impact rocks in the 1960s. Electron diffraction analysis coupled with scanning electron microscopy and Raman spectroscopy of shocked silica grains from the Australasian tektite/microtektite strewn field reveals fine-grained intergrowths of coesite plus quartz bearing planar deformation features (PDFs). Quartz and euhedral microcrystalline coesite are in direct contact, showing a recurrent pseudo iso-orientation, with the [11¯1]* vector of quartz near parallel to the [010]* vector of coesite. Moreover, discontinuous planar features in coesite domains are in textural continuity with PDFs in adjacent quartz relicts. These observations indicate that quartz transforms to coesite after PDF formation and through a solid-state martensitic-like process involving a relative structural shift of {1¯011}
quartz planes, which would eventually turn into coesite (010) planes. This process further explains the structural relation observed between the characteristic (010) twinning and disorder of impact-formed coesite, and the 101¯1 PDF family in quartz. If this mechanism is the main way in which coesite forms in impacts, a re-evaluation of peak shock pressure estimates in quartz-bearing target rocks is required because coesite has been previously considered to form by rapid crystallization from silica melt or diaplectic glass during shock unloading at 30-60 GPa.