¹N.P.S.Mithun et al. (>10)
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2020.104923]
¹Physical Research Laboratory, Ahmedabad, India

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^1,2M.R.Benedikt,¹M.Scherf,¹H.Lammer,³E.Marcq,²P.Odert,²M.Leitzinger,^4,5N.V.Erkaev
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113772]
¹Space Research Institute, Austrian Academy of Sciences, Schmiedlstraße 6, 8042 Graz, Austria
²Institute of Physics, IGAM, University of Graz, Universitätsplatz 5, 8010 Graz, Austria
³Université de Versailles St-Quentin-En-Yvelines, France
⁴Institute of Computational Modelling of the Siberian Branch of the Russian Academy of Sciences, 660036 Krasnoyarsk, Russian Federation
⁵Siberian Federal University, 660041 Krasnoyarsk, Russian Federation
Copyright Elsevier

Large planetesimals and planetary embryos ranging from several hundred to a few thousand kilometers can develop magma oceans through mutual collisions, gravitational energy, and the heating of short-lived radioactive elements. During their solidification after the dissipation of the disk a steam atmosphere will be catastrophically outgassed and may be lost efficiently via hydrodynamic escape, as long as it does not condense. The escaping H-atoms that originate from the dissociation of H₂O and H₂ will drag heavier trace elements like noble gases such as Ne and Ar and outgassed moderately volatile rock-forming elements such as K, Na, Si, Mg, etc. into space. Under consideration of various EUV flux evolution scenarios of young solar-type stars, we apply an upper atmosphere hydrodynamic escape model that includes the dragging of heavier species by escaping H-atoms. We investigate the atmospheric/elemental escape and fractionation from planetary embryos with masses of 1 M_Moon, 0.5 M_Mars, 1 M_Mars, and 1.5 M_Mars at different orbital distances between the orbits of Venus and Mars. Our results indicate that the steam atmospheres and the embedded trace elements will be lost efficiently before they condense for masses ≤0.5 M_Mars and orbital distances up to 1 AU. For heavier embryos of up to 1.5 M_Mars almost all of the considered steam atmospheres can be lost within ≈12 Myr, which lies within the time frame of the formation of the first Martian protocrust after ≈20 Myr, i.e. for such steam atmospheres to be lost completely a shallow magma ocean must remain below the atmosphere, which might be achieved through frequent impacts onto the planetary embryo. The considered outgassed noble gases and rock-forming elements will be completely dragged away together with the steam atmospheres under the assumption that the trace elements will reach the thermosphere. For embryos with masses ≤M_Moon the gravity is too weak for a dense atmosphere to build up for the high magma ocean related surface temperatures and all outgassed elements will escape immediately to space. For all considered planetary masses and orbits the loss rates of Ar and Ne are so high that there will be no fractionation of their isotopes. The studied planetary embryos, even though not isotopically fractionated, will therefore be severely depleted in noble gases and moderately volatile elements. Hydrodynamic escape might then also affect the final composition of terrestrial planets that accrete out of such planetary embryos, such as the volatile content and the Fe/Mg ratio of a planet.

¹Kim A.Cone,^1,2Richard M.Palin,¹Kamini Singh
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113787]
¹Geology and Geological Engineering Department, Colorado School of Mines, 1516 Illinois St., Golden, CO 80401, USA
²Department of Earth Sciences, University of Oxford, 3 South Parks Road, Oxford OX1 3AN, UK
Copyright Elsevier

Diversity of lunar basalt characteristics is partly a consequence of lunar mantle heterogeneity. Although the cumulate mantle overturn hypothesis is the current standard model invoked to explain mantle asymmetries of unknown length scale in both compositional and geometrical space, successful petrological modeling of this mixing event requires a specific set of parameters not currently agreed upon. In contrast, surface basalt patterns may yield clues to both localized and nearside lunar interior structure.

Using two multidimensional data analysis approaches – principal component analysis (PCA) and K-means cluster analysis (KCA) – we report the patterns produced from basalt characteristics over changing spatial scales, from intra-site to inter-site to nearside. The data are sourced from a newly developed, self-contained database of lunar basalt characteristics (ApolloBasaltDB), which includes major element oxides, mineral modes, ages, and textures for petrological and statistical modeling. Through the simultaneous considerations of multiple basalt characteristics contained in the database, we find that terrestrial-based basalt classifications cannot adequately describe the complex and overlapping distribution patterns of major element oxides and mineral modes that define multiple distinct basalt groupings over multidimensional space. These patterns provide opportunities for alternative lunar basalt classification schemes. Our analyses suggest that Al2O3 volumetric content is more diverse inside the Procellarum KREEP Terrane rift boundary versus content for older Apollo samples in close proximity to the eastern arm of the same rift boundary. Northernmost basalt samples show increased pyroxene diversity. Easternmost sites suggest anti-correlations in modal ilmenite and plagioclase, based on major element oxide PCA biplots, while nearside analyses of either major element oxides or mineral modes similarly suggest plagioclase (and Al2O3) diversity comes at the expense of ilmenite (and TiO2) diversity. There is evidence to suggest that approximate mineral content can be extracted from major element oxide data based on correlative patterns between major element oxide PCA biplots and mineral mode PCA biplots. These patterns have implications for remote sensing missions in that onboard data manipulation may provide lithologic basalt vectors of interest.

¹Paul H.Warren,¹Alan E.Rubin
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113771]
¹Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, CA 90095-1567, USA
Copyright Elsevier

The 14321 lunar granite (14321g) has recently been reinterpreted (Bellucci et al., 2019) as a piece of the Hadean Earth, impact-transported to the Moon. In principle, samples of such derivation may afford important insights into the nature of Earth’s Hadean crust. We have tested the terrestrial provenance hypothesis by comparing trace-element data from 14321g versus other lunar evolved rocks and a large data base for terrestrial granites. Volatile trace metals Zn, Ga and Ge are depleted in 14321g below the terrestrial granite ranges; and relative to the terrestrial granite averages by factors of 27, 2.0 and 18, respectively. Evidence from shocked chondrites, Martian meteorites, and impact-shock studies in general, indicates that such major depletions are unlikely to develop without near-complete shock-melting, which clearly did not occur in the mostly still-crystalline 14321g. Moreover, other aspects of compositional disparity between 14321g and terrestrial granites involve exclusively refractory trace elements. Compared to terrestrial granites of similarly high Ba content, 14321 is enriched in Ta by a factor of 10; and the few terrestrial granites that are as Ta-rich as 14321 have 10 times lower Ba. The refractory-element ratio Lu/Sm is also close to 10 times higher in 14321g than in terrestrial granites of similarly high Ba content. Other highly evolved lunar rocks, “felsites”, strongly resemble 14321g in all these respects. We conclude that 14321g is probably of wholly lunar derivation. This finding stands in contradiction to a recent inference from Ti-in-quartz modeling (Bellucci et al., 2019) that 14321g crystallized at a pressure of 0.69 GPa. The geodynamically limited Moon was presumably never capable of forming, or burying, such a highly granitic material ~100 km below the base of its crust, nor of excavating material from such a depth to the surface.

¹Damanveer S.Grewal,¹Rajdeep Dasgupta,^1,2Alexandra Farnell
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.04.023]
¹Department of Earth, Environmental, and Planetary Sciences, Rice University, 6100 Main Street, MS 126, Houston, TX 77005, USA
²St. John’s School, 2401 Claremont Ln, Houston, TX 77019, USA
Copyright Elsevier

The composition of the atmospheres and the resulting potential for planetary habitability in the rocky bodies of our Solar System and beyond is strongly controlled by the volatile exchange between their silicate reservoirs and exosphere. The initial budget and speciation of major volatiles, like carbon (C), nitrogen (N) and water (H₂O), in the silicate reservoirs and atmospheres was set during the formation stages of rocky bodies. However, the speciation of these major volatiles in reduced silicate melts prevalent during the differentiation stages of rocky bodies and its effect on the partitioning of volatiles between major rocky body reservoirs is poorly known. Here we present SIMS and vibrational spectroscopy (FTIR and Raman) data, determining C solubility, H content, and speciation of mixed C-O-N-H volatiles in graphite saturated silicate glasses from high P (1-7 GPa)-T (1500-2200 °C) experiments reported in Grewal et al. (2019b, 2019a). The experiments recorded oxygen fugacity (log fO₂) between IW–4.3 and IW–0.8. C-O-N-H speciation varied systematically as function of fO₂ at any given P–T. We find out that C≡N⁻, , N₂, and OH⁻ are the dominant species in the oxidized range (> IW–1.5), along with some contributions from C-H, N-H, and C≡O bearing species. Between IW–3.0 and IW–1.5, C is bonded as C≡O either in the form of isolated C≡O molecules or Fe-carbonyl complexes, or as C-H in hydrocarbons, or as combination of both in esters, while almost all of the H is bonded with the dominant N species, i.e., NH²⁻ or . At the most reduced conditions (<IW–3.0), C is present mostly in the form of C-H bearing species, while anhydrous N³⁻ followed by N-H bearing molecules are the dominant N bearing species. Magma oceans (MOs) in highly reduced bodies like Mercury would contain most of their C as graphite if MO is carbon saturated and the dissolved C and N would be chemically bonded with the silicate network either in the form of anhydrous C⁴⁻ and N³⁻, or hydrogenated C-H and N-H bearing species depending on H content of the silicate melts. MOs relevant for Mars, the Moon, Vesta, and angrite parent body would contain C and N mostly in the form of C≡O and N-H bearing species, respectively. If the composition of Earth’s accreting material evolved from reduced to oxidized, then initially a significant amount of the C and N budget would be locked in the silicate reservoirs, which would subsequently be released to the proto-atmosphere(s) at later stages. The retention of proto-atmosphere(s) formed by MO degassing on Earth could have provided important precursors for prebiotic chemistry which possibly led to the eventual habitability of our planet. Additionally, based on the dominant speciation of N versus C in silicate melt as a function of fO₂, we also predict that is unaffected by fH₂ under highly reduced conditions (< IW–3), while is. Therefore, caution must be taken during the application of experimentally determined and to nominally anhydrous MOs.

¹Zhen Tian,¹Bradley L.Jolliff,¹Randy L.Korotev,¹Bruce FegleyJr,¹Katharina Lodders,²James M.D.Day,^1,3Heng Chen,¹KunWang(王昆)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.04.021]
¹Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA
²Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, 92093 USA
³Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA
Copyright Elsevier

The Moon is depleted in water and other volatiles compared to Earth and the bulk solar composition. Such depletion of volatile elements and the stable isotope fractionations of these elements can be used to better understand the origin and early differentiation history of the Moon. In this study, we focus on the moderately volatile element, potassium, and we report the K elemental abundances and isotopic compositions (δ⁴¹K relative to NIST SRM 3141a) for nineteen Apollo lunar rocks and lunar meteorites (twenty-two subsamples), spanning all major geochemical and petrologic types of lunar materials. The K isotopic compositions of low-Ti and high-Ti basalts are indistinguishable, providing a lunar basalt average δ⁴¹K of –0.07 ± 0.09‰ (2SD), which we also consider to be the best estimate of the lunar mantle and the bulk silicate Moon. The significant enrichment of K in its heavier isotopes in the bulk silicate Moon, compared with the bulk silicate Earth (δ⁴¹K = –0.48 ± 0.03‰), is consistent with previous analyses of K isotopes and other moderately volatile elements (e.g., Cl, Cu, Zn, Ga, and Rb). We also report the first analyses of K isotopes for lunar nonmare samples, which show large variations of K isotopic ratios compared to lunar basalts. We interpret this large K isotopic fractionation as the result of late-stage magma ocean degassing during urKREEP formation, which is also coupled with Cl isotope fractionation. UrKREEP degassing likely triggered redistribution of K isotopes in the Moon, enriching the urKREEP reservoir in heavy K isotopes while implanting the light K isotopic signatures onto the lunar surface. This scenario suggests a heterogeneous distribution of K isotopes in the Moon as a consequence of its magmatic evolution.

^1,2K.H.Joy,¹R.Tartèse,³S.Messenger,^2,4M.E.Zolensky,⁵Y.Marrocchi,^4,6D.R.Frank,^2,7D.A.Kring
Earth and Planetary Science Letters 540,116265 Link to Article [https://doi.org/10.1016/j.epsl.2020.116265]
¹Department of Earth and Environmental Sciences, School of Natural Sciences, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK
²Center for Lunar Science and Exploration, The Lunar and Planetary Institute, 3600 Bay Area Blvd., Houston, TX 77058, USA
³Previously based at Robert M Walker Laboratory for Space Science, Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, TX 77058, USA
⁴XI2, Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, TX 77096, USA
⁵CRPG, CNRS, Université de Lorraine, UMR 7358, Vandoeuvre-les-Nancy, F-54501, France
⁶University of Hawai’i at Manoa Hawai’i Institute of Geophysics and Planetology, 1680 East-West Road, POST 602, Honolulu, HI 96822 USA1
⁷NASA Solar System Exploration Research Virtual Institute
Copyright Elsevier

Projectiles striking the Moon have modified its crust and delivered volatile elements to its interior and surface. Direct evidence of impactor origins is recorded by the rare occurrence of sub-cm sized meteorite fragments identified in Apollo samples and lunar meteorites. The Bench Crater meteorite is a millimetre-sized carbonaceous chondrite collected in regolith on the rim of Bench impact crater at the Apollo 12 landing site. Transmission electron microscopy has previously shown that Bench Crater contains abundant hydrated silicates, establishing the survivability of hydrated material impacting the lunar surface. To provide further information on the volatile inventory of the Bench Crater meteorite, we report here the isotope compositions of hydrogen, nitrogen, carbon and oxygen. This is the first direct isotopic analysis of meteoritic material delivered to the lunar surface and provides context for volatile and organic element signatures in lunar regolith samples, and the survivability of volatile material delivered to planetary surfaces during impact bombardment. The Bench Crater meteorite is characterised by δD values ranging between −36 ± 40 and 200 ± 40‰, and bulk average C of −13 ± 30‰, and N of −40 ± 36‰ (all uncertainties at the 2σ confidence level). The oxygen isotope compositions measured in situ in matrix silicates and magnetite in Bench Crater are consistent with those measured in matrix and magnetite in CI and CM chondrite falls. Altogether, these new H, C, N and O isotope data, coupled to mineralogical and geochemical observations, suggest that Bench Crater may have been derived from an asteroidal parent body not represented in the terrestrial meteorite collection. This is a crucial outcome in the current context of sample-return missions to carbonaceous asteroids, and more broadly for investigating the flux of material delivered to the Earth-Moon system through time.

¹Juan Diego Carrillo-Sánchez,¹David L.Bones,¹Kevin M.Douglas,²George J.Flynn,³Sue Wirick,⁴Bruce Fegley,⁵Tohru Araki,⁵Burkhard Kaulich,¹John M.C.Plane
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2020.104926]
¹School of Chemistry, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK
²State University of New York at Plattsburgh, Department of Physics, 101 Broad Street, Plattsburg, NY, 12901, USA
³Focused Beam Enterprises, Westhampton, NY, 11977, USA
⁴Planetary Chemistry Laboratory, Department of Earth & Planetary Sciences and McDonnell Center for the Space Sciences, Washington University, St Louis, MO, 63130, USA
⁵Diamond Light Source Ltd, Harwell Science & Innovation Campus, Didcot, OX11 0DE, UK

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¹Pavol Matlovič,¹Juraj Tóth,¹Leonard Kornoš,¹Stefan Loehle
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113817]
¹Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia
²High Enthalpy Flow Diagnostics Group, Institut für Raumfahrtsysteme, Universität Stuttgart, Pfaffenwaldring 29, D-70569 Stuttgart, Germany
Copyright Elsevier

The detected Na/Mg ratio in a sample of 17 Na-enhanced and Na-rich meteors is investigated based on obtained spectral, orbital and structural data. We utilize the meteor observations of the AMOS network obtained within a survey of medium-sized meteoroids supplemented by higher-resolution spectra observed on the Canary Islands. Ground-based meteor observations are then compared with high-resolution Echelle spectra of simulated ablation of known meteorite samples in a high-enthalpy plasma wind tunnel. It was found that most Na-enhanced and Na-rich spectra can be explained by the effect of low meteor speed related to low ablation temperatures and generally do not reflect real meteoroid composition. Spectra obtained by the laboratory experiment simulating low meteor speeds show corresponding Na-rich profiles irrespectively of the meteorite composition. We estimate that for an H-type ordinary chondrite with speed of  10 km s^-1, the Na line intensity is increased by a factor of 40 to 95. The dynamical analysis has revealed that all Na-rich meteors originated on Apollo-type orbits and exhibit consistent chondritic material strengths. For more clarity in the classification of Na-enhanced and Na-rich meteoroids, we propose new speed-dependent boundaries between the spectral classes. Real compositional Na enhancement was confirmed in five cometary meteoroids: two Perseids, a -Capricornid, -Draconid and a sporadic. The two Na-enhanced Perseids were linked with increased material strength suggesting that the detected increase of volatile content has implications for the meteoroid structure.

¹Thomas Kenkmann,¹Gerwin Wulf,^1,2Amar Agarwal
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.1345]
¹Institute of Earth and Environmental Sciences—Geology, Albert‐Ludwigs‐Universität Freiburg, Albertstrasse 23‐B, 79104 Freiburg im Breisgau, Germany
²Department of Earth Sciences, Indian Institute of Technology‐Kanpur, Kanpur‐208016, India
Published by arrangement with John Wiley & Sons

The Ramgarh structure is a morphological landmark in southeastern Rajasthan, India. Its 200 m high and 3.5–4 km wide annular collar has provoked many hypotheses regarding its origin, including impact. Here, we document planar deformation features, planar fractures, and feather features in quartz grains of the central part of the Ramgarh structure, which confirm its impact origin. The annular collar does not mark the crater rim but represents the outer part of a central uplift of an approximately 10 km diameter complex impact structure. The apparent crater rim is exposed as a low‐angle normal fault and can be traced as lineaments in remote sensing imagery. The central uplift shows a stratigraphic uplift of ~1000 m and is rectangular in shape. It is dissected by numerous faults that are co‐genetic with the formation of the central uplift. The central uplift has a bilateral symmetry along an SW‐NE axis, where a large strike‐slip fault documents a strong horizontal shear component. This direction corresponds to the assumed impact trajectory from the SW toward the NE. The uprange sector is characterized by concentric reverse faults, whereas radial faults dominate downrange. Sandstones of the central uplift are infiltrated by Fe‐oxides and suggest an impact‐induced hydrothermal mineralization overprint. The impact may have occurred into a shallow water environment as indicated by soft‐sediment deformation features, observed near the apparent crater rim, and the deposition of a diamictite layer above them. Gastropods embedded in the diamictite have Middle Jurassic age and may indicate the time of the impact.