^1,2Thomas B. Leith, ¹Nicholas A. Moskovitz, ³Rhiannon G. Mayne, ⁴Francesca E. DeMeo, ⁵Driss Takir, ^1,4Brian J. Burt, ⁴Richard P. Binzel, ⁴Dimitra Pefkou
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2017.05.007]
¹Lowell Observatory, Flagstaff, AZ, 86001, USA
²Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, 02138, USA
³Monnig Meteorite Collection, Texas Christian University, Fort Worth, TX, 76129, USA
⁴Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
⁵Astrogeology Science Center, United States Geological Survey, Flagstaff, AZ, 86001, USA
Copyright Elsevier

We present near-infrared (0.78-2.45 μm) reflectance spectra for nine middle and outer main belt (a > 2.5 AU) basaltic asteroids. Three of these objects are spectrally distinct from all classifications in the Bus-DeMeo system and could represent spectral end members in the existing taxonomy or be representatives of a new spectral type. The remainder of the sample are classified as V- or R-type. All of these asteroids are dynamically detached from the Vesta collisional family, but are too small to be intact differentiated parent bodies, implying that they originated from differentiated planetesimals which have since been destroyed or ejected from the solar system. The 1- and 2-μm band centers of all objects, determined using the Modified Gaussian Model (MGM), were compared to those of 47 Vestoids and fifteen HED meteorites of known composition. The HEDs enabled us to determine formulas relating Band 1 and Band 2 centers to pyroxene ferrosilite (Fs) compositions. Using these formulas we present the most comprehensive compositional analysis to date of middle and outer belt basaltic asteroids. We also conduct a careful error analysis of the MGM-derived band centers for implementation in future analyses. The six outer belt V- and R-type asteroids show more dispersion in parameter space than the Vestoids, reflecting greater compositional diversity than Vesta and its associated bodies. The objects analyzed have Fs numbers which are, on average, between five and ten molar percent lower than those of the Vestoids; however, identification and compositional analysis of additional outer belt basaltic asteroids would help to confirm or refute this result. Given the gradient in oxidation state which existed within the solar nebula, these results tentatively suggest that these objects formed at either a different time or location than 4 Vesta.

¹Maria Eugenia Varela, ²Ernst Zinner
Geochmica et Cosmochmica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2017.03.038]
¹ICATE-CONICET, Av. España 1512 Sur, San Juan, Argentina
²Laboratory for Space Sciences and Physics Department, Washington University, St. Louis, MO 63130, USA
Copyright Elsevier

The process/es involved in chondrule formation cover a wide range of mechanisms whose nature is still unknown. Our attention is focused on solar nebula processes mainly in untangling the origin of the initial liquid droplets that turn into chondrules. To do this, we start deciphering the processes under which the chondritic constituents of glass-rich, PO and POP chondrules from the Unequilibrated Ordinary Chondrite (UOC) Tieschitz L/H3.6 could have been formed. One constituent is the initial refractory liquid. This chilled liquid, presented as primary glass inclusions in olivine or as glass mesostasis, has trace element abundances with unfractionated patterns and lacks the chemical signature that is expected from a geochemical (liquid-crystal) fractionation. The unfractionated crystal-liquid distribution coefficients observed in the glass-rich, PO and POP chondrules indicate that formation of these objects was not dominated by an igneous process. In addition, the good correlation of elements with different geochemical and cosmochemical properties (e.g., Yb and La-Ce) that spread around the primordial ratio, indicate that a cosmochemical (condensation) instead of a geochemical process may have been involved in the origin of this refractory liquid. We end up discussing a secondary process: the alkali-Ca exchange reaction that could have taken place within a cooling nebula at sub-solidus temperatures. The extent to which these solid/gas exchange reactions took place will determine the final composition of the chondrules.

¹Dayl J. P. Martin,¹John F. Pernet-Fisher,¹Katherine H. Joy,¹Roy A. Wogelius,²Andreas Morlok,²Harald Hiesinger
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12860]
¹School of Earth and Environmental Sciences, University of Manchester, Manchester, UK
²Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Münster, Germany
Published by arrangement with John Wiley & Sons

Fourier transform infrared (FTIR) spectroscopy and cathodoluminescence (CL) imaging techniques, combined with electron microprobe analyses, have been used to determine the physical state of feldspathic phases that have been subject to varying levels of shock in the grouped lunar meteorites Miller Range 090034, 090070, and 090075. Six feldspathic phases have been identified based on spectral, textural, and chemical properties. A specific infrared wavelength band ratio (1064/932 cm−1 equivalent to 9.40/10.73 μm), chosen because it can distinguish between some of the feldspathic phases, can be used to estimate the pressure regimes experienced by these phases. In addition, FTIR spatial mapping capabilities allow for visual comparison of variably shocked phases within the samples. By comparing spectral and compositional data, the origin and shock history of this lunar meteorite group has been determined, with each of the shocked feldspathic phases being related to events in its geological evolution. As such, we highlight that FTIR spectroscopy can be easily employed to identify shocked feldspathic phases in lunar samples; estimate peak shock pressures; and when compared with chemical data, can be used to investigate their shock histories.

¹J. Leitner, ¹P. Hoppe, ²C. Floss, ³F. Hillion, ⁴T. Henkel
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2017.05.003]
¹Max Planck Institute for Chemistry, Particle Chemistry Department, Hahn-Meitner-Weg 1, 55128 Mainz, Germany
²Laboratory for Space Sciences and Physics Department, Washington University, One Brookings Drive, St. Louis, MO 63130, USA
³Cameca, Gennevilliers, France
⁴The University of Manchester, School of Earth and Environmental Sciences, Williamson Building, Oxford Road, Manchester, M13 9PL, UK
Copyright Elsevier

We report the light to intermediate-mass element abundances as well as the oxygen, magnesium, silicon, and titanium isotope compositions of a unique and unusually large (0.8 µm × 3.75 µm) presolar O-rich grain from the Krymka LL3.2 chondrite. The O-, Al-, and Ti-isotopic compositions are largely compatible with an origin from an asymptotic giant branch (AGB) star of 1.5 solar masses with a metallicity that is 15% higher than the solar metallicity. The grain has an elevated 17O/16O ratio (8.40 ± 0.16 × 10–4) compared to solar, and slightly sub-solar 18O/16O ratio (1.83 ± 0.03 × 10–3). It shows evidence for the presence of initial 26Al, suggesting formation after the first dredge-up, during one of the early third dredge-up (TDU) episodes. Titanium isotopic data indicate condensation of the grain before significant amounts of material from the He-burning shell were admixed to the stellar surface with progressive TDUs. We observed a small excess in 30Si (δ30Si = 41 ± 5 ‰), which most likely is inherited from the parent star’s initial Si-isotopic composition. For such stars stellar models predict a C/O-ratio

The grain is an unusual complex presolar grain, consisting of an Al-Ca-Ti-oxide core, surrounded by an Mg-Ca-silicate mantle, and resembles the condensation sequence for a cooling gas of solar composition at pressures and dust/gas ratios typically observed for circumstellar envelopes around evolved stars. We also report the first observation of phosphorus in a presolar grain, although the origin of the P-bearing phase remains ambiguous.

^1,2Thomas Stephan, ^1,2Reto Trappitsch, ^1,2,3Andrew M. Davis, ^1,2,3,4Michael J. Pellin, ^1,2Detlef Rost, ^2,3Michael R. Savina, ^1,2Manavi Jadhav, ^1,2Christopher H. Kelly, ^1,5Frank Gyngard, ^1,6Peter Hoppe, ^1,2,3Nicolas Dauphas
Geochmica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2017.05.001]
¹Department of the Geophysical Sciences, The University of Chicago, Chicago, IL 60637, USA
²Chicago Center for Cosmochemistry, Chicago, IL, USA
³The Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637, USA
⁴Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
⁵Laboratory for Space Sciences and Department of Physics, Washington University, St. Louis, MO 63130, USA
⁶Max Planck Institute for Chemistry, 55128 Mainz, Germany
Copyright Elsevier

We used CHILI, the Chicago Instrument for Laser Ionization, a new resonance ionization mass spectrometer developed for isotopic analysis of small samples, to analyze strontium, zirconium, and barium isotopes in 22 presolar silicon carbide grains. Twenty of the grains showed detectable strontium and barium, but none of the grains had enough zirconium to be detected with CHILI. Nine grains were excluded from further consideration since they showed very little signals (<1000 counts) for strontium as well as for barium. Among the 11 remaining grains, we found three X grains. The discovery of three supernova grains among only 22 grains was fortuitous, because only ∼1% of presolar silicon carbide grains are type X, but was confirmed by silicon isotopic measurements of grain residues with NanoSIMS. While one of the X grains showed strontium and barium isotope patterns expected for supernova grains, the two other supernova grains have ⁸⁷Sr/⁸⁶Sr < 0.5, values never observed in any natural sample before. From their silicon isotope ratios, the latter two grains can be classified as X2 grains, while the former grain belongs to the more common X1 group. The differences of these grains in strontium and barium isotopic composition constrain their individual formation conditions in Type II supernovae.

¹Lisseth Gavilan, ²Laurent Remusat, ²Mathieu Roskosz, ³Horia Popescu, ³Nicolas Jaouen, ⁴Christophe Sandt, ⁵Cornelia Jäger, ⁶Thomas Henning, ⁷Alexandre Simionovici, ⁸Jean Louis Lemaire
The Astrophysical Journal 840, 35 Link to Article [https://doi.org/10.3847/1538-4357/aa6bfc]
¹LATMOS, Université Versailles St Quentin, UPMC Université Paris 06, CNRS, 11 blvd d’Alembert, F-78280 Guyancourt, France
²IMPMC, CNRS UMR 7590; Sorbonne Universités, UPMC Université Paris 06; IRD, Muséum National d’Histoire Naturelle, CP 52, 57 rue Cuvier, Paris F-75231, France
³SEXTANTS beamline, SOLEIL synchrotron, L’Orme des Merisiers, F-91190 Saint-Aubin, France
⁴SMIS beamline, SOLEIL synchrotron, L’Orme des Merisiers, F-91190 Saint-Aubin, France
⁵Laboratory Astrophysics and Cluster Physics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University & Institute of Solid State Physics, Helmholtzweg 3, D-07743 Jena, Germany
⁶Max-Planck Institute for Astronomy Königstuhl 17, D-69117 Heidelberg, Germany
⁷Institut des Sciences de la Terre, Observatoire des Sciences de l’Univers de Grenoble, BP 53, F-38041 Grenoble, France
⁸Institut des Sciences Moléculaires d’Orsay (ISMO), CNRS, Univ. Paris Sud, Université Paris-Saclay, F-91405 Orsay, France
⁹Institut Jean Lamour, CNRS, Université de Lorraine, F-54011 Nancy, France

The deuterium enrichment of organics in the interstellar medium, protoplanetary disks, and meteorites has been proposed to be the result of ionizing radiation. The goal of this study is to simulate and quantify the effects of soft X-rays (0.1–2 keV), an important component of stellar radiation fields illuminating protoplanetary disks, on the refractory organics present in the disks. We prepared tholins, nitrogen-rich organic analogs to solids found in several astrophysical environments, e.g., Titan’s atmosphere, cometary surfaces, and protoplanetary disks, via plasma deposition. Controlled irradiation experiments with soft X-rays at 0.5 and 1.3 keV were performed at the SEXTANTS beamline of the SOLEIL synchrotron, and were immediately followed by ex-situ infrared, Raman, and isotopic diagnostics. Infrared spectroscopy revealed the preferential loss of singly bonded groups (N–H, C–H, and R–N≡C) and the formation of sp3 carbon defects with signatures at ~1250–1300 cm−1. Raman analysis revealed that, while the length of polyaromatic units is only slightly modified, the introduction of defects leads to structural amorphization. Finally, tholins were measured via secondary ion mass spectrometry to quantify the D, H, and C elemental abundances in the irradiated versus non-irradiated areas. Isotopic analysis revealed that significant D-enrichment is induced by X-ray irradiation. Our results are compared to previous experimental studies involving the thermal degradation and electron irradiation of organics. The penetration depth of soft X-rays in μm-sized tholins leads to volume rather than surface modifications: lower-energy X-rays (0.5 keV) induce a larger D-enrichment than 1.3 keV X-rays, reaching a plateau for doses larger than 5 × 1027 eV cm−3. Synchrotron fluences fall within the expected soft X-ray fluences in protoplanetary disks, and thus provide evidence of a new non-thermal pathway to deuterium fractionation of organic matter.

¹J.B. Creech, ^1,2F. Moynier, ³M. Bizzarro
Geochmica et Cosmochmica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2017.04.040]
¹Institut de Physique du Globe de Paris, Université Sorbonne Paris Cité, Université Paris Diderot, 1 Rue Jussieu, 75328 Paris cedex 05, France
²Institut Universitaire de France, 75005, Paris, France
³Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen, Denmark
Copyright Elsevier

Stable isotope studies of highly siderophile elements (HSE) have the potential to yield valuable insights into a range of geological processes. In particular, the strong partitioning of these elements into metal over silicates may lead to stable isotope fractionation during metal–silicate segregation, making them sensitive tracers of planetary differentiation processes. We present the first techniques for the precise determination of palladium stable isotopes by MC-ICPMS using a 106Pd–110Pd double-spike to correct for instrumental mass fractionation. Results are expressed as the per mil (‰) difference in the 106Pd/105Pd ratio (δ106Pd) relative to an in-house solution standard (Pd_IPGP) in the absence of a certified Pd isotopic standard. Repeated analyses of the Pd isotopic composition of the chondrite Allende demonstrate the external reproducibility of the technique of ± 0.032‰ on δ106Pd. Using these techniques, we have analysed Pd stable isotopes from a range of terrestrial and extraterrestrial samples. We find that chondrites define a mean δ106Pdchondrite= –0.19 ± 0.05‰ . Ureilites reveal a weak trend towards heavier δ106Pd with decreasing Pd content, similar to recent findings based on Pt stable isotopes (Creech et al., 2017, Geochem. Persp. Let. 3, 94–104), although fractionation of Pd isotopes is significantly less than for Pt, possibly related to its weaker metal–silicate partitioning behaviour and the limited field shift effect. Terrestrial mantle samples have a mean δ106Pdmantle = –0.182 ± 0.130‰ , which is consistent with a late-veneer of chondritic material after core formation.

¹C.R. Kuchka, ¹C.D.K. Herd, ^1,2E.L. Walton, ³Y. Guan, ^3,4Y. Liu
Geochmica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2017.04.037]
¹University of Alberta, Department of Earth and Atmospheric Sciences, Edmonton, AB, T6G 2E3, Canada
²MacEwan University, Department of Physical Sciences, Edmonton, AB T5J 4S2, Canada
³Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
⁴Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
Copyright Elsevier

We apply an array of in situ analytical techniques, including electron and Raman microscopy, electron and ion probe microanalysis, and laser ablation mass spectrometry to the Tissint martian meteorite in order to find and elucidate a geochemical signature characteristic of low-temperature alteration at or near the martian surface. Tissint contains abundant shock-produced quench-crystallized melt pockets containing water in concentrations ranging from 73 to 1730 ppm; water content is positively correlated with Cl content. The isotopic composition of hydrogen in the shock-produced glass ranges from δD = 2559 to 4422 ‰. Water is derived from two distinct hydrogen reservoirs: the martian near-surface (>500 ‰) and the martian mantle (-100 ‰). In one shock melt pocket comprising texturally homogeneous vesiculated glass, the concentration of H in the shock melt decreases while simultaneously becoming enriched in D, attributable to the preferential loss of H over D to the vesicle while the pocket was still molten. While igneous sulfides are pyrrhotite in composition (Fe0.88-0.90S), the iron to sulfur ratios of spherules in shock melt pockets are elevated, up to Fe1.70S, which we attribute to shock-oxidation of igneous pyrrhotite and the formation of hematite at high temperature. The D- and Cl-enrichment, and higher oxidation of the pockets (as indicated by hematite) support a scenario in which alteration products formed within fractures or void spaces within the rock; the signature of these alteration products is preserved within shock melt (now glass) which formed upon collapse of these fractures and voids during impact shock. Thermal modeling of Tissint shock melt pockets using the HEAT program demonstrates that the shock melt pockets with the greatest potential to preserve a signature of aqueous alteration are small, isolated from other regions of shock melt, vesicle-free, and glassy.

¹Davide Lenaz,²Birger Schmitz
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12885]
¹Department of Mathematics and Geosciences, University of Trieste, Trieste, Italy
²Division of Nuclear Physics, Department of Physics, Lund University, Lund, Sweden
Published by arrangement with John Wiley & Sons

Six Cr-spinel grains from NWA 6077 brachinite-like and NWA 725 winonaite achondrites have been studied by single-crystal X-ray diffraction and structural refinement. From a chemical point of view, spinels from NWA 6077 show Cr/(Cr + Al) (i.e., Cr#) and Mg/(Mg + Fe2+) (i.e., Mg#) values similar to other brachinites, while the Cr# of NWA 725 is lower than that of literature winonaites. Spinels from NWA 6077 and NWA 725 meteorites show similar cell edges, while the oxygen positional parameter is rather different being about 0.2629 for NWA 6077 and 0.2622 for NWA 725. Considering both parameters, NWA 725 shows structural features that are close to some terrestrial spinel occurrences as in komatiites, kimberlites, or included in diamonds; those from NWA 6077 show values that have no terrestrial analogs. Olivine-chromite closure temperature ranges from ~737 to ~765° C for NWA 725, being similar to that of literature winonaites and ~846 to ~884° C for NWA 6077. The logfO2 ranges from −19.8 to −20.5 and −17.0 to −17.9 for the two meteorites, respectively. The u values for terrestrial samples can give information about the cooling history of the samples. For the extraterrestrial samples, it seems that it can give information about the cooling only for spinels where it is lower than 0.2625. For higher values, it appears related only to the chemistry of the spinels.

¹Dwijesh Ray,²Dewashish Upadhyay,³Saumitra Misra,⁴Horton E. Newsom,¹Sambhunath Ghosh
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12881]
¹Planetary Sciences Division, Physical Research Laboratory, Ahmedabad, India
²Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur, India
³Discipline of Geological Sciences, SAEES, University of KwaZulu-Natal, Durban, South Africa
⁴Institute of Meteoritics and Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA
Published by arrangement with John Wiley & Sons

The Lonar impact crater, India, is one of the few known terrestrial impact craters excavated in continental basaltic target rocks (Deccan Traps, ~65 Ma). The impactites reported from the crater to date mainly include centimeter- to decimeter-sized impact-melt bombs, and aerodynamically shaped millimeter- and submillimeter-sized impact spherules. They occur in situ within the ejecta around the crater rim and show schlieren structure. In contrast, non–in situ glassy objects, loosely strewn around the crater lake and in the ejecta around the crater rim do not show any schlieren structure. These non–in situ fragments appear to be similar to ancient bricks from the Daityasudan temple in the Lonar village. Synthesis of existing and new major and trace element data on the Lonar impact spherules show that (1) the target Lonar basalts incorporated into the spherules had undergone minimal preimpact alteration. Also, the paleosol layer as preserved between the top-most target basalt flow and the ejecta blanket, even after the impact, was not a source component for the Lonar impactites, (2) the Archean basement below the Deccan traps were unlikely to have contributed material to the impactite parental melts, and (3) the impactor asteroid components (Cr, Co, Ni) were concentrated only within the submillimeter-sized spherules. Two component mixing calculations using major oxides and Cr, Co, and Ni suggest that the Lonar impactor was a EH-type chondrite with the submillimeter-sized spherules containing ~6 wt% impactor components.