¹M. Arif,²Saumitra Misra
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13643]
¹Indian Institute of Geomagnetism, Navi Mumbai, 410218 India
²Discipline of Geological Sciences, SAEES, University of KwaZulu‐Natal, Durban, 4000 South Africa
Published by arrangement with John Wiley & Sons

The continuous ejecta deposit around the rim of Lonar impact crater, central India, contains angular basaltic boulders of size ≤5 m. These boulders experienced varying level of shock between 2–30 GPa due to impact, as indicated by the extreme fracturing of these basaltic boulders, fragmentation of plagioclase and titanomagnetite constituents of these ejected boulders, and the presence of maskelynite in them. We measure some rock magnetic properties, e.g., NRM/χ (natural remanent magnetization [NRM]/bulk magnetic susceptibility [χ]), REM (=NRM/saturation isothermal remanent magnetization [SIRM] ratio expressed in %), and anisotropy of magnetic susceptibility (AMS) on 53 subsamples from 18 oriented drill cores of the shocked ejected basaltic boulders from the eastern half of ejecta deposit in the present study. The measured data are similar in many respects to our previous observations on Lonar crater rim shocked basalts (Arif et al. 2012b). For example, a small population of the ejected basaltic boulder samples show very high NRM/χ (between 378 and 989 Am−1; n = 7) and REM (between 1.5 and 7%; n = 4) and the AMS axes of these ejected basaltic boulders show triaxial distributions in stereographic projections. Moreover, some of the ejected basaltic boulders show higher values of squareness ratio (Mrs/Ms) and median destructive field (MDF) suggesting permanent changes in the intrinsic magnetic properties due to impact shock pressure. In stereographic plot, the high coercivity and high temperature (HC_HT) magnetization component of these ejected basaltic boulders are distributed in discrete clusters on the periphery of a small enveloping circle whose center (D = 108.0°, I = +69.2°) lies close to the HC_HT cluster of the crater rim shocked basalts. The center of this enveloping circle and the average HC_HT component of Lonar crater rim shocked basalts have the same statistical orientation, although the former has steeper dip. This distribution suggests the possibility that the ejected basaltic boulders, which were deposited during the modification stage of Lonar crater evolution, were magnetized in an impact‐induced magnetic field that was rapidly decaying just after the impact. Our present study suggests that the ejected basaltic boulders and Lonar crater rim shocked basalts experienced high shock pressure (≥2 GPa) magnetization during impact.

^1,2Ekaterina V. Korochantseva,¹Alexei I. Buikin,¹Jens Hopp,³Alexander B. Verchovsky,¹Alexander V. Korochantsev,^3,4Mahesh Anand,¹Mario Trieloff
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13632]
¹Institut für Geowissenschaften, Klaus‐Tschira‐Labor für Kosmochemie, Universität Heidelberg, Im Neuenheimer Feld 234‐236, 69120 Heidelberg, Germany
²Vernadsky Institute of Geochemistry, Kosygin St. 19, 119991 Moscow, Russia
³School of Physical Sciences, The Open University, Milton Keynes, MK7 6AA UK
⁴Department of Earth Sciences, The Natural History Museum, London, SW7 5BD UK
Published by arrangement with John Wiley & Sons

The lunar meteorite Dhofar 1436 is dominated by solar wind type noble gases. Solar argon is equilibrated with “parentless” 40Ar commonly known as lunar orphan argon. Ar‐Ar isochron analyses determined the lunar trapped 40Ar/36Ar ratio to 2.51 ± 0.04, yielding a corrected plateau age of 4.1 ± 0.1 Ga, consistent with the lunar Late Heavy Bombardment period. Lunar trapped and radiogenic argon components are all released at high temperatures (1200–1400 °C). Surprisingly, solar noble gases and lunar trapped argon can largely be released by crushing. Initial crushing steps mainly release elementally fractionated solar wind gases, while in advanced crushing steps, cosmogenic components dominate. Cosmogenic noble gases indicate irradiation at the lunar surface; they are less fractionated than solar wind species. We favor a scenario in which both solar and a large fraction of cosmogenic gases were acquired before the 4.1 Ga event, which caused shock metamorphism and formation of the regolith breccia. Sintering and agglutination along grain boundaries resulted in mobilization of solar wind, reimplanted, radiogenic, and cosmogenic noble gases, and resulted in their partial homogenization, fractionation, and retrapping in voids and/or defects accessible by crushing. An alternative scenario would be complete reset of the K‐Ar system 4.1 Ga ago accompanied by loss of all previously accumulated solar and cosmogenic noble gases. Later, the precursor of Dhofar 1436 became lunar regolith and accumulated solar and cosmogenic noble gases and reimplanted 40Ar before its final formation of the polymict impact breccia. The C abundance of the step‐combusted Dhofar 1436 is 555.3 ppm, with δ13C of −28‰ to +11‰. Nitrogen contents released by crushing and combustion are 3.2 ppm and 20.8 ppm, respectively. The lightest nitrogen composition (δ15N = −79‰) is likely due to release from voids of shock metamorphic phases and is rather a result of the mobilization of nitrogen components that accumulated prior to the 4.1 Ga event.

¹J. Brossier,¹M.S. Gilmore,¹K. Toner,¹A.J. Stein
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2020JE006722]
¹Wesleyan University, Department of Earth and Environmental Sciences, Planetary Sciences Group, 265 Church Street, Middletown, CT, 06459 USA
Published by arrangement with John Wiley & Sons

NASA’s Magellan mission revealed that many Venus highlands exhibit low radar emissivity values at higher altitudes. This phenomenon is ascribed to the presence of minerals having high dielectric constants, produced or stabilized by temperature‐dependent chemical weathering between the rocks and the atmosphere. Some large volcanoes on Venus have multiple reductions of radar emissivity at varying altitudes. We present morphological maps of major lava flow units at Maat, Ozza and Sapas montes and compare them to radar emissivity. Sapas has a single reduction in emissivity values at 6054.6 km, while Maat and Ozza have several reductions at altitudes of 6052.5–6056.7 km. Emissivity values are highly spatially correlated to individual lava flows indicating that minerals in the rocks control the emissivity signature. The emissivity patterns at these volcanoes require at least 4 individual ferroelectric mineral compositions in the rocks that are highly conductive at Curie temperatures of 693–731 K. These temperatures are compatible with chlorapatite and some perovskite oxides. Modeling the minimum volumes of ferroelectrics (10s–100s ppm) shows the volume and type of ferroelectric may vary over the lifetime of a single volcano. The modeled volumes of ferroelectrics in Ozza and Sapas are greater than in Maat, consistent with the production of ferroelectrics via weathering over a longer period of time, and supporting the idea that Maat has younger volcanic activity. The stratigraphic relationship of Maat’s youngest flows with impact craters may indicate the timeframe of the production of specific ferroelectrics via chemical weathering is over 9–60 Ma.

¹Romain Tartèsea,²Paolo A. Sossi,³Frédéric Moynier
Proceedings of the National Academy of Sciences of teh United States of America (PNAS) (in Press) Link to Article [DOI: https://doi.org/10.1073/pnas.2023023118]
¹Department of Earth and Environmental Sciences, The University of Manchester, M13 9PL Manchester, United Kingdom;
²Institute of Geochemistry and Petrology, ETH Zürich, CH-8092 Zürich, Switzerland;
³Université de Paris, Institut de Physique du Globe de Paris, CNRS UMR 7154, 75005 Paris, France

Rocks from the lunar interior are depleted in moderately volatile elements (MVEs) compared to terrestrial rocks. Most MVEs are also enriched in their heavier isotopes compared to those in terrestrial rocks. Such elemental depletion and heavy isotope enrichments have been attributed to liquid–vapor exchange and vapor loss from the protolunar disk, incomplete accretion of MVEs during condensation of the Moon, and degassing of MVEs during lunar magma ocean crystallization. New Monte Carlo simulation results suggest that the lunar MVE depletion is consistent with evaporative loss at 1,670 ± 129 K and an oxygen fugacity +2.3 ± 2.1 log units above the fayalite-magnetite-quartz buffer. Here, we propose that these chemical and isotopic features could have resulted from the formation of the putative Procellarum basin early in the Moon’s history, during which nearside magma ocean melts would have been exposed at the surface, allowing equilibration with any primitive atmosphere together with MVE loss and isotopic fractionation.

^1,2Mingming Zhang,³Brett Clark,^1,4Ashley J. King,¹Sara S. Russell,²Yangting Lin
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13635]
¹Department of Earth Sciences, The Natural History Museum, Cromwell Road, SW7 5BD London, UK
²Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
³Core Research Laboratories, The Natural History Museum, Cromwell Road, SW7 5BD London, UK
⁴School of Physical Sciences, The Open University, Walton Hall, MK7 6AA Milton Keynes, UK
Published by arrangement with John Wiley & Sons

Refractory calcium‐aluminum‐rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs) in chondritic meteorites are the earliest solids of our solar system, bearing the information of nebular condensation as well as accretion and asteroidal shock and metasomatism processes. While the compositions of refractory inclusions have been intensely studied for ~50 years, their physical properties such as shape and porosity are poorly constrained. Here, we present a microcomputed tomography (µCT) study on 16 refractory inclusions of condensate origin in five CV3 chondrites. We find that they are prolate or triaxial in shape with very rough morphologies. The CAIs have nodular textures and are thought to form by agglomerating individual nodules via collision‐induced bouncing and/or fragmentation, where the nodules were grown by gas–solid reactions during condensation. On the parent body, refractory inclusions from the CVR meteorite Leoville experienced intense shocks that led to the flattening of their shapes and lowering of their porosities. High‐temperature metasomatism in CVOxA meteorites and low‐temperature metasomatism in CVOxB meteorites do not seem to have large effects on the porosities of their refractory inclusions, which have similar ranges and pore‐size distributions. Instead, we infer that their pores are mostly inherited from the gas–solid condensation and subsequent agglomeration processes. The porosities of CAIs are higher than those of AOAs, which is mainly due to the high‐temperature sintering process of AOAs.

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.