¹J.I.Simon,^1,2R.Christoffersen,³J.Wang,¹M.D.Mouser,⁴R.D.Mills,^1,2,5D.K.Ross,²Z.Rahman,³C.M.O’D.Alexander
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.02.008]
¹Center for Isotope Cosmochemistry and Geochronology, Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, TX 77058, USA
²Jacobs, NASA Johnson Space Center, Mail Code XI3, Houston, TX 77058, USA
³Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015-1305, USA
⁴Department of Geological Sciences, University of North Carolina, Chapel Hill, NC 27599, USA
⁵University of Texas at El Paso/Jacobs-JETS, Houston, TX 77058, USA
Copyright Elsevier

In this detailed geochemical, petrological, and microstructural study of felsite clast materials contained in Apollo breccia samples 12013, 14321, and 15405, little evidence was found for relatively enriched reservoirs of endogenic lunar volatiles. NanoSIMS measurements have revealed very low volatile abundances (≤2 to 18 ppm hydrogen) in nominally anhydrous minerals (NAMS) plagioclase, potassic alkali feldspar, and SiO₂ that make up a majority of these felsic lithologies. Yet these mineral assemblages and clast geochemistries on Earth would normally yield relatively high volatiles contents in their NAMS (∼20 to ≥80 ppm hydrogen). This difference is particularly notable in felsite 14321,1062 that exhibits extremely low volatile abundances (≤2 ppm hydrogen) and a relatively low amount of microstructural evidence for shock metamorphism given that it is a clast of the most evolved (∼74 wt. % SiO₂) rock-type returned from the Moon. If taken at face value, ‘wet’ felsic magmas (∼1.2 to 1.7 wt. % water) are implied by the relatively high hydrogen contents of feldspar in felsite clasts in Apollo samples 12013 and 15405, but these results are likely misleading. These felsic clasts have microstructural features indicative of significantly higher shock stress than 14321,1062. These crustal lithologies likely obtained no more water from the lunar interior than the magma body producing 14321,1062. Rather, we suggest hydrogen was enriched in samples 12013 and 15405 by impact induced exchange, and/or partial assimilation of volatiles added to the surface of the Moon by a hydrated impactor (asteroid or comet) or the solar wind. Thus, the best estimate for magmatic water contents of felsic lunar magmas comes from 14321,1062 that leads to a calculated magmatic water content of ≤0.2 wt.%. This dry felsic magma has a slightly greater, but comparable water content to the ancient mafic magmas implied by the other lithologies that we have studied. Based on this and expanding evidence for a significantly dry ancient or early degassed Moon it is likely that some recent estimates (100’s ppm) of the water abundances in the lunar parental magma ocean have been overestimated.

¹G. Avice,¹M. Moreira,²J. D. Gilmour
The Astrophysical Journal 889, 68 Link to Article [DOI
https://doi.org/10.3847/1538-4357/ab5f0c]
¹Unversité de Paris, Institut de physique du globe de Paris, CNRS, F-75005 Paris, France
²Department of Earth and Environmental Science, School of Natural Sciences, University of Manchester, Manchester, M13 9PL, UK

Nucleosynthetic isotopic anomalies in meteorites and planetary objects contribute to our understanding of the formation of the solar system. Isotope systematics of chondrites demonstrate the existence of a physical separation between isotopic reservoirs in the solar system. The isotopic composition of atmospheric xenon (Xe) indicates that its progenitor, U-Xe, is depleted in ¹³⁴Xe and ¹³⁶Xe isotopes relative to solar or chondritic end-members. This deficit supports the view that nucleosynthetic heterogeneities persisted during the solar system formation. Measurements of xenon emitted from comet 67P/Churyumov–Gerasimenko (67P) identified a similar, but more extreme, deficit of cometary gas in these isotopes relative to solar gas. Here we show that the data from 67P demonstrate that two distinct sources contributed xenon isotopes associated with the r-process to the solar system. The h-process contributed at least 29% (2σ) of solar system ¹³⁶Xe. Mixtures of these r-process components and the s-process that match the heavy isotope signature of cometary Xe lead to depletions of the precursor of atmospheric Xe in p-only isotopes. Only the addition of pure p-process Xe to the isotopic mixture brings ¹²⁴Xe/¹³²Xe and ¹²⁶Xe/¹³²Xe ratios back to solar-like values. No pure p-process Xe has been detected in solar system material, and variation in p-process Xe isotopes is always correlated with variation in r-process Xe isotopes. In the solar system, p-process incorporation from the interstellar medium happened before incorporation of r-process nuclides or material in the outer edge of the solar system carries a different mixture of presolar sources as have been preserved in parent bodies.

^1,2Kołodziej, M.,¹Śniadecki, Z.,¹Musiał, A.,³Pierunek, N.,⁴Ivanisenko, Y.,⁵Muszyński, A.,¹Idzikowski, B.
Journal of Magnetism and Magnetic Materials 502, 166577 Link to Article [DOI: 10.1016/j.jmmm.2020.166577]
¹Institute of Molecular Physics, Polish Academy of Sciences, Mariana Smoluchowskiego 17, Poznań, 60-179, Poland
²NanoBioMedical Centre, Adam Mickiewicz University in Poznań, Wszechnicy Piastowskiej 3, Poznań, 61-614, Poland
³Quantum Electronics Laboratory, Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, Poznań, 61-614, Poland
⁴Institute of Nanotechnology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, Eggenstein-Leopoldshafen, D-76344, Germany
⁵Institute of Geology, Adam Mickiewicz University, Bogumiła Krygowskiego 12, Poznań, 61-680, Poland

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¹Allegretta, I.,²Marangoni, B.,³Manzari, P.,¹Porfido, C.,¹Terzano, R.,⁴De Pascale, O.,⁴ Senesi, G.S.
Talanta 212, 120785 Link to Article [DOI: 10.1016/j.talanta.2020.120785]
¹Dipartimento di Scienze del Suolo, della Pianta e degli Alimenti, Università degli Studi di Bari “Aldo Moro”, Via Amendola 165/A, Bari, 70126, Italy
²Physics Institute, Federal University of Mato Grosso do Sul, P.O. Box 549, Campo Grande, MS 79070-900, Brazil
³Agenzia Spaziale Italiana, via del Politecnico, Roma, 00133, Italy
⁴CNR – Istituto per la Scienza e Tecnologia dei Plasmi (ISTP) – Sede di Bari, Via Amendola 122/D, Bari, 70126, Italy

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¹Gismelssed, A.,²Okunlola, O.,¹Al-Rawas, A.,¹Yousif, A.,²Oyedokun, M.,³Adetunji, J.,¹Widatallah, H.,¹Elzai, M.
Hyperfine Interactions 241, 22 Link to Article [DOI: 10.1007/s10751-019-1683-7]
¹Physics Department, College of Science, Sultan Qaboos university, Muscat, Oman
²Department of Geology University of Ibadan, Ibadan, Nigeria
³School of Environmental Sciences, University of Derby, Kedleston Road, Derby, DE22 1GB, United Kingdom

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¹Ferreira, L.M.G.,²Alves, E.I.,³Gonçalves, M., Costa,¹B.F.O.
Hyperfine Interactions 241, 19 Link to Article [DOI: 10.1007/s10751-019-1685-5]
¹CFisUC, Physics Department, University of Coimbra, Coimbra, P-3004-516, Portugal
²CITEUC and Department of Earth Sciences, University of Coimbra, Coimbra, P-3040-004, Portugal
³NEO SKytale, Rua Santiago 30, Castelo Branco, P-6000-179, Portugal

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¹JeffA.Berger,²M.E.Schmidt,¹J.L.Campbell,¹E.L.Flannigan,¹R.Gellert,³W.Ming,³R.V.Morris
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113708]
¹University of Guelph, Guelph, Canada
²Brock University, St. Catharines, Canada
³NASA Johnson Space Center, Houston, USA
Copyright Elsevier

The Alpha Particle X-ray Spectrometer (APXS), a field instrument onboard four martian rovers, measures largely unprepared, in situ samples on Mars. The APXS has high precision that enables the determination of elemental concentrations in a wide range of geologic materials. However, lack of sample preparation can lead to heterogeneous matrix effects, and understanding the associated uncertainty is essential for interpreting APXS data. Here we use Particle Induced X-ray Emission spectrometry (PIXE) to analyze a suite of geologic samples from Hawai’i as an analogue study to better understand APXS analyses of martian samples. Wavelength-Dispersive X-ray Fluorescence (WDXRF) analyses of fused glass beads establish higher-accuracy standards for the Hawaiian samples. Sulfate-silicate mixtures were made to evaluate sulfur analysis by PIXE. Results show that the PIXE concentrations for most major elements have 2–6% accuracy, which is comparable to the APXS. However, the PIXE concentrations are systematically high in Al and low in Mg, resulting in lower accuracy (13% and 20%, respectively). Olivine-phyric lavas and most of their altered products have the largest discrepancies with Al concentrations up to 25% high and Mg up to 35% low. Sulfur is systematically high (up to 30% in a basalt matrix) compared to gravimetric S concentrations in the sulfate-silicate mixtures. These systematic deviations in Mg, Al, and S are linked to heterogeneous matrix effects, because PIXE and APXS analyses assume all atoms in a sample to be homogeneously mixed on the sub-micrometer scale, which is not the case. Two key implications for APXS results are: (1) Olivine-bearing samples likely have reported concentrations of Mg that is too low and Al that is too high. Thus, olivine-phyric basalts in Gusev crater and the basaltic sand and soil at three landing sites may have Mg and Al concentrations closer to those of the olivine-phyric shergottites and modelled martian crust than previously thought. (2) Sulfate-silicate mixtures may have overestimated S concentrations reported, resulting in greater uncertainty in the stoichiometry of Ca-sulfates, which is used to deduce the geochemical associations of sulfur in samples.

¹Xiaoqing Xu,^1,2Hejiu Hui,³Wei Chen,⁴Shichun Huang,⁵Clive R.Neal,¹XishengXu
Earth and Planetary Science Letters 536, 116138 Link to Article [https://doi.org/10.1016/j.epsl.2020.116138]
¹State Key Laboratory of Mineral Deposits Research & Lunar and Planetary Science Institute, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
^sCAS Center for Excellence in Comparative Planetology, Hefei 230026, China
³State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China
⁴Department of Geoscience, University of Nevada, Las Vegas, NV 89154, United States
⁵Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN 46556, United States
Copyright Elsevier

The lunar magma ocean (LMO) model was proposed after the discovery of anorthosite in Apollo 11 samples. However, the chemical and isotopic compositions of lunar anorthosites are not fully consistent with its LMO origin. We have analyzed major and trace elements in anorthositic clasts from ten lunar feldspathic meteorites, which are related to the solidification of the LMO. The plagioclase rare earth element (REE) abundances and patterns are not correlated with the Mg# of coexisting mafic minerals in anorthosites, implying that mafic minerals and plagioclase may not be in chemical equilibrium, consistent with their textural differences. The REE abundances in plagioclase range approximately fortyfold, which cannot be produced by fractional crystallization of a single magma. Combining plagioclase trace element data from Apollo and meteoritic anorthosites, we propose that plagioclases derived from the LMO floated to the surface to form the primordial crust, which then may have been metasomatized by incompatible-element-rich KREEP (potassium, rare earth element, phosphorus) melts and mantle-derived partial melts. The lunar anorthosites may represent this metasomatized crust rather than solely a derivative from the LMO. Furthermore, silicate melts similar to the metasomatic agents may also have melted the crust to form the Mg-suite rocks. This hypothesis is consistent with overlapping ranges of age and initial ε_Nd between lunar anorthosites and Mg-suite rocks. These events are consistent with an overturn event of the cumulate mantle very early after primordial crust formation to produce the partial melts that metasomatized the crust.

¹Vlastimil Vojáček,¹Jiří Borovička,¹Pavel Spurný,¹David Čapek
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2020.104882]
¹Astronomical Institute of the Czech Academy of Sciences, Fričova 298, 251 65, Ondřejov, Czech Republic

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¹A.Galiano,¹F.Dirri,^1,2E.Palomba,¹ A.Longobardo,³B.Schmitt,³P.Beck
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113692]
¹INAF-IAPS, Rome, Italy
²SSDC-ASI, Rome, Italy
³Université Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France
Copyright Elsevier

The dwarf planet Ceres is an airless body composed of Mg-phyllosilicates, NH₄-phyllosilicates, Mg/Ca-carbonates and a dark component. The subsurface of Ceres, investigated by the material composing the peak of complex craters (ccp, crater central peak material; Galiano et al., 2019), reveals a composition similar to the surface, with an increasing abundance of phyllosilicates in the interior. A moderate trend between age of craters’ formation and spectral slope of ccps suggests that younger ccps show a negative/blue slope and older ccps are characterized by positive/red slope. To investigate the causes of different spectral slope in ccps, different grain-sized Ceres analogue mixtures were produced and spectrally analysed. First, the end-members of the Ceres surface (using the antigorite as Mg-phyllosilicate, the NH₄-montmorillonite as NH₄-phyllosilicate, the dolomite as carbonate and the graphite as dark component), were mixed, obtaining mixtures with different relative abundance, and identifying the mixture with the reflectance spectrum most similar to the average Ceres spectrum. The selected mixture was reproduced with grain size of 0–25 μm, 25–50 μm and 50–100 μm. The three mixtures were heated and spectrally analysed, both with an acquisition temperature of 300 K (room temperature) and 200 K (typical for surface Ceres temperature during VIR observations).

The best analogue Ceres spectrum is coincident with a mixture composed of 18 M% (mass percentage) of Dolomite, 18 M% of Graphite, 36 M% of Antigorite and 28 M% of NH₄-montmorillonite, after experiencing a heating process.

The heating process produces: 1) a darkening and reddening of spectrum, as consequence of the devolatilization of OH group in phyllosilicates and a more dominant effect of opaque phase; 2) a deepening in the intensity of the 3.4 and 4.0 μm band, as well as the 2.7 and the 3.1 μm band, likely due to the loss of absorbed atmospheric water; 3) narrowing of 3.1 μm band and the shift of band center toward longer wavelength (i.e. at 3.06 μm) coincident with mean Ceres spectrum, related to the loss of absorbed atmospheric water.

The analysis of the best Ceres analogue mixture, reproduced at different grain size and after heating process, reveals a weakening of 2.7, 3.1, 3.4 and 4.0 absorption bands in coarser samples, likely related to large size of dark grains which reduce the spectral contrast. Furthermore, spectra of coarser mixtures are more red-sloped, suggesting that this trend is more affected by the dark component.

The best analogue Ceres mixture produced in this work is almost coincident with the mean spectrum of Haulani ccp, the youngest ccps on Ceres and therefore representative of less altered material on Ceres.

The redder spectral slope observed in the older ccps is probably the consequence of the space weathering effects on the original material composing the peak.