¹Barbara Cosciotti,¹Sebastian Emanuel Lauro,¹Francesco Gabbai,¹Elisabetta Mattei,²Federico Di Paolo,^3,4Giovanni Pratesi,¹Elena Pettinelli
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114426]
¹Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre, Via della Vasca Navale, 00146 Roma, Italy
²Dipartimento di Scienze e Tecnologie, Università degli Studi di Napoli “Parthenope”, Naples 80143, Italy
³Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via Giorgio La Pira 4, 50121 Firenze, Italy
⁴INAF – Istituto di Astrofisica e Planetologia Spaziali, Via Fosso del Cavaliere 100, 00133 Roma, Italy
Copyright Elsevier

Ground Penetrating Radar (GPR) is a terrestrial geophysical exploration method that has recently become one of the most promising technique for planetary, asteroidal and cometary subsurface exploration. The capability of GPR to sound Solar System’s bodies relies on the electromagnetic properties of the constitutive materials. Enstatite and ordinary chondrites represent class of asteroids occurring in the inner asteroid belt whereas carbonaceous chondrites and their icy mixtures are reasonable analogues for cometary material as well as constituent of shallow part of some Jovian satellite crusts. Therefore, the knowledge of electromagnetic properties of meteorites is very important because it allows to estimate the radar response in terms of signal velocity and attenuation. In this work we measured the real and imaginary parts of the permittivity of a L5 chondrite meteorite as a function of frequency (20 Hz-1 MHz) by using a capacitive cell connected to a self-balancing bridge. We studied the spatial variability of dielectric properties of the sample that exhibits areas with different textures characterized by a darker appearance. In general, the meteorite sample shows a stronger dispersive behavior compared to terrestrial rocks with higher values for both real and imaginary part of permittivity. In particular, the occurrence of very small grains (<10 μm) of Fesingle bondNi metal, troilite and chromite scattered in some areas of the meteorite seems to be the cause of such behavior.

¹T.Ootsubo,¹H.Kawakita,²²Y.Shinnaka
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114425]
¹National Astronomical Observatory of, Japan
²Koyama Astronomical Observatory, Kyoto, Sangyo Univ., Japan
Copyright Elsevier

We present mid-infrared observations of comet P/2016 BA14 (PANSTARRS), which were obtained on UT 2016 March 21.3 at heliocentric and geocentric distances of 1.012 au and 0.026 au, respectively, approximately 30 h before its closest approach to Earth (0.024 au) on UT 2016 March 22.6. Low-resolution (λ/Δλ ~ 250) spectroscopic observations in the N-band and imaging observations with four narrow-band filters (centered at 8.8, 12.4, 17.7 and 18.8 μm) in the N- and Q-bands were obtained using the Cooled Mid-Infrared Camera and Spectrometer (COMICS) mounted on the 8.2-m Subaru telescope atop Maunakea, Hawaii. The observed spatial profiles of P/2016 BA14 at different wavelengths are consistent with a point-spread function. Owing to the close approach of the comet to the Earth, the observed thermal emission from the comet is dominated by the thermal emission from its nucleus rather than its dust coma. The observed spectral energy distribution of the nucleus at mid-infrared wavelengths is consistent with a Planck function at temperature T ~ 350 K, with the effective diameter of P/2016 BA14 estimated as ~0.8 km (by assuming an emissivity of 0.97). The normalized emissivity spectrum of the comet exhibits absorption-like features that are not reproduced by the anhydrous minerals typically found in cometary dust coma, such as olivine and pyroxene. Instead, the spectral features suggest the presence of large grains of phyllosilicate minerals and organic materials. Thus, our observations indicate that an inactive small body covered with these processed materials is a possible end state of comets.

¹Matthew R.M.Izawa,²Daniel M.Applin,³Matthew Q.Morison,¹Edward A.Cloutis,¹Paul Mann,⁴Stanley A.Mertzman
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114423]
¹Institute for Planetary Materials, Okayama University, 827 Yamada, Misasa, Tottori 682-0193, Japan
²Department of Geography, University of Winnipeg, Winnipeg, Manitoba R3B 2E9, Canada
³Department of Geography, University of Waterloo, Waterloo, Ontario N2L 2B5, Canada
⁴Department of Earth and Environment, Franklin and Marshall College, Lancaster, PA 17604, USA
Copyright Elsevier

Ilmenite is an important mineral for understanding lunar evolution. Ilmenite is also a primary ore of titanium on the Earth. Here we present a comprehensive examination of the spectral-compositional-structural relationships of ilmenites and related Fesingle bondTi oxides. Ilmenite spectral features of interest include maxima near ~250 nm (due Ti4+-O and Fe2+-O charge transfers), ~335 nm (due to Fe2+-Ti4+ charge transfer), and 950 nm (interband maximum), and absorption features near ~540 nm (due to Fe2+-Ti4+ charge transfers), ~630 nm (due to Ti3+-Ti4+ charge transfers), and a ~ 1300/1600 nm absorption doublet (due to Fe2+ crystal field transitions). Absorption features transition from Fresnel peaks to valley around 400 nm, as absorption coefficients decrease toward longer wavelengths. Ilmenite powders are generally darkest and show the greatest spectral contrast and reflectance rise beyond ~1300 nm for the smallest grain sizes. Other Ti and Fesingle bondTi oxides share some spectral properties with ilmenites but also exhibit many differences. The most common feature they share is a rise in reflectance toward shorter wavelengths below ~500 nm (i.e., blue spectral slope). Ti ± Fe oxide spectra can also exhibit absorption features attributable to Ti, Fe, and Ti ± Fe, and these features vary in intensity, shape and wavelength position due to factors such as Ti and Fe oxidation states, coordination environment, and nearest neighbor cation types. Ilmenite differs most from silicates in the region below ~500 nm: it shows a reflectance increase versus decrease toward shorter wavelengths for silicates, as well as diagnostic Ti/Ti-Fe maxima or minima. Thus, detection of ilmenite in mixtures is best accomplished by including the UV region in spectral analysis. With increasing ilmenite in mixtures, its diagnostic spectral features become increasingly apparent.

¹A.Praet et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114427]
¹LESIA, Observatoire de Paris, Université PSL, CNRS, Université de Paris, Sorbonne Université, 5 place Jules Janssen, 92195 Meudon, France
Copyright Elsevier

Asteroids were likely a major source of volatiles and water to early Earth. Quantifying the hydration of asteroids is necessary to constrain models of the formation and evolution of the Solar System and the origin of Life on Earth. The OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) mission showed that near-Earth asteroid (101955) Bennu contains widespread, abundant hydrated phyllosilicates, indicated by a ubiquitous absorption at ~ 2.7 μm. The objective of this work is to quantify the hydration—that is, the hydrogen content—of phyllosilicates on Bennu’s surface and investigate how this hydration varies spatially. We analyse spectral parameters (normalized optical path length, NOPL; effective single-scattering albedo, ESPAT; and Gaussian modeling) computed from the hydrated phyllosilicate absorption band of spatially resolved visible–near-infrared spectra acquired by OVIRS (the OSIRIS-REx Visible and InfraRed Spectrometer). We also computed the same spectral parameters using laboratory-measured spectra of meteorites including CMs, CIs, and the ungrouped C2 Tagish Lake. We estimate the mean hydrogen content of water and hydroxyl groups in hydrated phyllosilicates on Bennu’s surface to be 0.71 ± 0.16 wt%. This value is consistent with the hydration range of some aqueously altered meteorites (CMs, C2 Tagish Lake), but not the most aqueously altered group (CIs). The sample collection site of the OSIRIS-REx mission has slightly higher hydrogen content than average. Spatial variations in hydrogen content on Bennu’s surface are linked to geomorphology, and may have been partially inherited from its parent body.

¹Keisuke Muneishi,¹Hiroshi Naraoka
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13614]
¹Department of Earth and Planetary Sciences, Kyushu University, 744 Motooka, Nishi‐ku, Fukuoka, 819‐0395 Japan
Published by arrangement with John Wiley & Sons

Olivine is a principal anhydrous silicate mineral in chondritic meteorites. The structure of this mineral is composed of independent SiO4 tetrahedra linked by divalent cations (mainly Mg). Under hydrothermal conditions, olivine is transformed into serpentine, which is a major hydrated phyllosilicate in the matrix of carbonaceous chondrites. Although carbonaceous chondrites contain various types of organic matter, the interaction between organic compounds and olivine at low temperature has not been considered in the literature. We performed an experiment to test the adsorption of N‐containing organic compounds (i.e., alkylpyridines and alkylimidazoles) on olivine using liquid chromatography under aqueous conditions (pH = 2.5–10.5) at 20–40 °C. The N‐containing cyclic compounds were interacted with the SiO4 tetrahedra of olivine and their different adsorption abilities depended on the organic structures. Because alkylpyridines often occur at different locations than alkylimidazoles in carbonaceous chondrites, the results of this study suggest that olivine can separate the N‐containing compounds associated with aqueous fluid flows by asteroidal chromatography in the meteorite parent body. Liquid chromatography based on solid phase minerals may hence be a useful technique for simulating the behavior of organic compounds in carbonaceous asteroids under aqueous activity.

¹Jean-Alix Barrata,²Marc Chaussidon,³Akira Yamaguchi,⁴Pierre Beck,⁵Johan Villeneuve,⁵David J. Byrne,⁵Michael W. Broadley,⁵Bernard Marty
Proceedings of the National Academy of Sciences of the United States of America (PNAS) (in Press) Link to Article [https://doi.org/10.1073/pnas.2026129118]
¹Univ Brest, CNRS, IRD, Ifremer, LEMAR, F-29280 Plouzané, France;
²Institut de physique du globe de Paris, CNRS, Université de Paris, F-75005 Paris, France;
³National Institute of Polar Research, Tachikawa, Tokyo 190-8518, Japan;
⁴CNRS, Institut de Planetologie et d’Astrophysique de Grenoble, F-38400 Saint Martin d’Hères, France;
⁵Université de Lorraine, CNRS, CRPG, F-54000 Nancy, France

The age of iron meteorites implies that accretion of protoplanets began during the first millions of years of the solar system. Due to the heat generated by 26Al decay, many early protoplanets were fully differentiated with an igneous crust produced during the cooling of a magma ocean and the segregation at depth of a metallic core. The formation and nature of the primordial crust generated during the early stages of melting is poorly understood, due in part to the scarcity of available samples. The newly discovered meteorite Erg Chech 002 (EC 002) originates from one such primitive igneous crust and has an andesite bulk composition. It derives from the partial melting of a noncarbonaceous chondritic reservoir, with no depletion in alkalis relative to the Sun’s photosphere and at a high degree of melting of around 25%. Moreover, EC 002 is, to date, the oldest known piece of an igneous crust with a 26Al-26Mg crystallization age of 4,565.0 million years (My). Partial melting took place at 1,220 °C up to several hundred kyr before, implying an accretion of the EC 002 parent body ca. 4,566 My ago. Protoplanets covered by andesitic crusts were probably frequent. However, no asteroid shares the spectral features of EC 002, indicating that almost all of these bodies have disappeared, either because they went on to form the building blocks of larger bodies or planets or were simply destroyed.

¹Zachary A.Torrano,^1,2Devin L.Schrader,^1,2Jemma Davidson,^cRichard C.Greenwood,¹Daniel R.Dunlap,¹Meenakshi Wadhwa
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.03.004]
¹School of Earth and Space Exploration, Arizona State University, Tempe, AZ, 85287, USA
²Center for Meteorite Studies, Arizona State University, Tempe, AZ, 85287, USA
³Planetary and Space Sciences, School of Physical Sciences, The Open University, Milton Keynes, MK7 6AA, United Kingdom
Copyright Elsevier

A close relationship between CM and CO chondrites has been suggested by previous petrologic and isotopic studies, leading to the suggestion that they may originate from similar precursor materials or even a common parent body. In this study, we evaluate the genetic relationship between CM and CO chondrites using Ti, Cr, and O isotopes. We first provide additional constraints on the ranges of ε50Ti and ε54Cr values of bulk CM and CO chondrites by reporting the isotopic compositions of CM2 chondrites Murchison, Murray, and Aguas Zarcas and the CO3.8 chondrite Isna. We then report the ε50Ti and ε54Cr values for several ungrouped and anomalous carbonaceous chondrites that have been previously reported to exhibit similarities to the CM and CO chondrite groups, including Elephant Moraine (EET) 83226, EET 83355, Grosvenor Mountains (GRO) 95566, MacAlpine Hills (MAC) 87300, MAC 87301, MAC 88107, and Northwest Africa (NWA) 5958, and the oxygen isotope compositions of a subset of these samples. We additionally report the ε50Ti, ε54Cr, and O isotopic compositions of additional ungrouped chondrites LaPaz Ice Field (LAP) 04757, LAP 04773, Lewis Cliff (LEW) 85332, and Coolidge to assess their potential relationships with known carbonaceous and ordinary chondrite groups. LAP 04757 and LAP 04773 exhibit isotopic compositions indicating they are low-FeO ordinary chondrites. The isotopic compositions of Murchison, Murray, Aguas Zarcas, and Isna extend the compositional ranges defined by the CM and CO chondrites in ε50Ti versus ε54Cr space. The majority of the ungrouped carbonaceous chondrites with documented similarities to the CM and/or CO chondrites plot outside the CM and CO group fields in plots of ε50Ti versus ε54Cr,Δ17O versus ε50Ti, and Δ17O versus ε54Cr. Therefore, based on differences in their Ti, Cr, and O-isotopic compositions, we conclude that the CM, CO, and ungrouped carbonaceous chondrites likely represent samples of multiple distinct parent bodies. We also infer that these parent bodies formed from precursor materials that shared similar isotopic compositions, which may indicate formation in regions of the protoplanetary disk that were in close proximity to each other.

¹Kei Shimizu,¹ConelM. O’D. Alexander,¹Erik H.Hauri,²Adam R.Sarafian,¹Larry R.Nittler,¹Jianhua Wang,³Steven D.Jacobsen,⁴Ruslan A.Mendybaev
Geochimica et Cosmochimica Acta (in Press) Link to Artiel [https://doi.org/10.1016/j.gca.2021.03.005]
¹Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC
²Science and Technology Division, Corning Incorporated, Corning, NY
³Dept. of Earth and Planetary Sciences, Northwestern University, Evanston, IL
⁴Dept. of Geophysical Sciences, University of Chicago, Chicago, IL
Copyright Elsevier

The partial pressures and isotopic compositions of volatiles present during chondrule formation can be constrained by the highly volatile element or HVE (H, C, F, Cl, and S) abundances and isotopic compositions in chondrules. Here we present the results of high spatial resolution and low background secondary ion mass spectroscopy (SIMS) analyses of the HVE concentrations and H isotopic compositions in type I and II chondrules in primitive ordinary chondrites Semarkona (LL3.00) and Queen Alexandra Range (QUE) 97008 (L3.05), and the primitive carbonaceous chondrite Dominion Range (DOM) 08006 (CO3.00). The HVEs in the chondrules primarily reside in the mesostases, in which the HVE contents and H isotopic compositions vary significantly (H2O: 8–10,200 ppm, CO2: 2.4–1170 ppm, F: 0.3–30 ppm, Cl: 0.07–175 ppm, S: 0.38–4400 ppm, δD: 77–15,000‰). To dissolve such HVE contents in a silicate melt requires significantly higher total pressures (up to 1900 bars), and in some cases requires anomalous gas compositions (CO dominated), compared to those expected from canonical conditions of chondrule formation (∼10-3 bars, H2+H2O dominated). Rather, the enrichments of H2O, CO2, Cl, and F in the mesostases at the edges of some chondrules suggest that there were secondary influxes of HVEs into the chondrule mesostases from the surrounding matrix during parent body processes. Consistent with this, melt inclusions sealed in olivine phenocrysts have significantly lower HVE contents than the mesostases in contact with the surrounding matrix material. Further, the calculated diffusion distances of H2O in silicate glasses under the relevant conditions are comparable to the radii of the chondrules. The high δD values in the mesostases could have been generated through isotopic Rayleigh fractionation as a result of the loss of very D-poor H2 generated from Fe metal oxidation by H2O in the parent bodies. Based on these results, we hypothesize that the bulk of the HVEs in the chondrules are secondary in origin. However, a small portion of the HVEs in chondrules could be primary, as there are low but measurable amounts of HVEs in the melt inclusions that are sealed in phenocrysts. Further, measured S contents in some chondrule mesostases agree with those predicted in a sulfide saturated silicate melt based on an experimentally calibrated thermodynamic model. We constrain the upper limits of primary HVEs in the chondrules based on the lowest measured HVE contents to minimize the effects of the secondary influx of HVEs (type I H2O: 7–11 ppm, CO2: 0.3–0.6 ppm, F: 0.1–0.2 ppm, Cl: 0.01–0.03 ppm, S: 0.3–60 ppm, and type II H2O: 50–85 ppm, CO2: 0.4–3 ppm, F: 0.04–2 ppm, Cl: 0.04–2 ppm, S: 190–260 ppm).

¹Ben Kumler,¹James M.D.Day
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.03.002]
¹Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0244, USA
Copyright Elsevier

Eucrite meteorites are early-formed (>4.5 Ga) basaltic rocks that are likely to derive from the asteroid 4 Vesta, or a similarly differentiated planetesimal. To understand trace element and moderately volatile element (MVE) behavior more fully within and between eucrites, a laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) study is reported for plagioclase and pyroxene, as well as fusion crust and vitrophyric materials for ten eucrites. These eucrites span from a cumulate eucrite (Northwest Africa [NWA] 1923) to samples corresponding to Main Group (Queen Alexandra Range 97053, Pecora Escarpment 91245, Cumulus Hills 04049, Bates Nunatak 00300, Lewis Cliff 85305, Graves Nunataks 98098) and Stannern Group (Allan Hills 81001, NWA 1000) compositions, in addition to Elephant Moraine 90020. Along with a range of refractory trace elements, focus was given to abundances of five MVE (K, Zn, Rb, Cs, Pb) to interrogate the volatile abundance distributions in eucrite mineral phases. Modal recombination analyses of the eucrites reveals the important role of accessory phases (zircon, apatite) in some of the incompatible trace element (ITE) distributions, but not for the MVE which, for the phases that were analyzed, are mostly sited within plagioclase (Cs, Rb, K) and pyroxene (Zn, Pb), and are in equilibrium with a parental melt composition for Main Group eucrites. The new data reveal a possible relationship with total refractory ITE enrichment and texture, with the most ITE enriched Stannern Group eucrites examined (NWA 1000, ALHA 81001) having acicular textures and, in the case of ALHA 81001 a young degassing age (∼3.7 Ga). Collectively the results suggest that Stannern Group eucrites may be related to anatexis of the eucritic crust by thermal metamorphism, with the heat source possibly coming from impacts. Impact processes do not have a pronounced effect on the abundances of the MVE, where plagioclase, pyroxene, fusion crust, and whole rock compositions of eucrites are all significantly depleted in the MVE, with Zn/Fe, Rb/Ba and K/U similar to lunar rocks. Assessment of eucrite compositions, however, suggests that Vesta has a more heterogeneous distribution of volatile elements and is similarly to slightly less volatile-depleted than the Moon. Phase dependence of the MVE (e.g., Cl in apatite, Zn primarily into spinel and early formed phases, including pyroxene) is likely to influence comparison diagrams where MVE stable isotopes are shown. In the case of δ37Cl versus δ66Zn, metamorphism and impact processes may lead to a decrease in the δ37Cl value for a given δ66Zn value in eucrites, raising the possibility that late-stage impact and metamorphism had a profound effect on volatile distributions in early planetesimal crusts.

¹Morgan A. Cox,¹Aaron J. Cavosie,²Michael H. Poelchau,²Thomas Kenkmann,²Katarina Miljković,²Phil A. Bland
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13621]
¹Space Science and Technology Centre (SSTC), School of Earth and Planetary Sciences, Curtin University, Perth, Western Australia, 6102 Australia
²Institute of Earth and Environmental Sciences—Geology, Albert‐Ludwigs‐Universität (ALU) Freiburg, Albertstraße 23B, Freiburg, 79104 Germany
Published by arrangement with John Wiley & Sons

The distribution of shock deformation effects, as well as the structural expression of an impact structure, can be asymmetric, depending on target rock lithologies (e.g., layered versus homogenous), porosity of target rock, and angle of impact. Here, we present a detailed study of shock‐deformed quartz and zircon in silicified sandstones from the asymmetric Spider impact structure in Australia. We utilize optical microscopy and electron backscatter diffraction (EBSD) techniques in order to determine the spatial distribution of shock‐deformed zircon along a downrange transect across the central uplift of the structure, with the goal of constraining the physical distribution of shock effects created by an oblique impact. A total of 453 zircon grains from 12 samples of shatter cone‐bearing quartzite and breccia within the structure were surveyed for shock deformation by EBSD in situ within thin sections. Nineteen zircon grains contain {112} twins, including one grain with three twin orientations. Quartz grains from five samples along the transect were also surveyed using a universal stage in order to determine orientations of planar deformation features, planar fractures, and feather features, and to provide a baseline for comparison of data from zircon. The distribution of shocked zircon with {112} twins within the samples surveyed appears to be asymmetric relative to the center of the structure, in contrast to quartz, thus providing the first accessory mineral‐based evidence that supports an asymmetric distribution of shock deformation as a function of impact obliquity. Our results are an example where the highest intensity of observed shock deformation does not correspond to the geographic center of the structure, and may serve as a guide for field studies aimed at documenting the distribution of shock effects at other sites interpreted to result from oblique impacts.