Global Hydrogen Abundances on the Lunar Surface

1David J. Lawrence,1Patrick N. Peplowski,1Jack T. Wilson,2Richard C. Elphic
Journal of Geophysical research (Planets) (in Press) Open Access Link to Article [https://doi.org/10.1029/2022JE007197]
1Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, United States
2NASA Ames Spaceflight Center, Moffett Field, California, United States
Published by arrangement with John Wiley & Sons

A global map of bulk hydrogen abundances on the Moon is presented. This map was generated using data from the Lunar Prospector Neutron Spectrometer. This map required corrections for variations due to rare-earth elements, and was calibrated to Apollo sample hydrogen abundances. Since neutron-derived measurements sample hydrogen content to a depth of tens of cm, these results provide complementary insights to those provided by studies using spectral reflectance data, which sample depths of order μm. Comparison of these abundances to Apollo sample values suggest that the samples reflect actual hydrogen content on the lunar surface, not dominantly from non-lunar contamination. The average lunar hydrogen abundance is 47 ppm with a systematic uncertainty of ∼10 ppm. This is consistent with bulk hydrogen from solar wind emplacement. A bulk hydrogen enhancement (50–68 ppm) has been identified at the Moon’s largest pyroclastic deposit (Aristarchus Plateau), which corroborates prior observations that hydrogen and/or water plays a role in lunar magmatic events. Global data show a correlation between hydrogen and evolved materials rich in incompatible trace elements (i.e., KREEP type rocks), with a hydrogen excess of 14–36 ppm in these materials. Based on this hydrogen enhancement, we estimate a lower-limit water abundance within urKREEP materials (i.e., the final ∼2% of the lunar magma ocean) of 320–820 ppm H2O. This observation implies that water played a role in the original magma-ocean formation and solidification with a lower-limit water content in the original lunar magma ocean of 7–16 ppm or higher.

Thermal conductivity of basalt between 225 and 290 K

1D. Halbert,1J. Parnell
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13829]
1School of Geosciences, University of Aberdeen, King’s College, Meston Building, Aberdeen, AB24 3UE UK
Published by arrangement with John Wiley & Sons

Thermal conductivity of natural rock is only well characterized for temperatures above 273 K, i.e., at typical Earth values. In planetary science, there is a requirement to explore the thermal characteristics of rock at temperatures below 273 K, for which thermal conductivity data are sparse or contested. Here, we present empirical data for a basalt showing thermal conductivity ranging from 2.71 ± 0.09 W m−1 K−1 at 224.4 K, to 2.63 ± 0.05 W m−1 K−1 at 288.8 K. Previous work reports much lower values in this range, which may be due to the fragmented nature of the previous research, the use of powdered samples for some data, and the effect of porosity. The high-temperature thermal conductivity laws of Sass et al. (1992) and Haenel and Zoth (1973) can be robustly extrapolated to cover the temperature range of our data.

Geologically rapid aqueous mineral alteration at subfreezing temperatures in icy worlds

1Amber Zandanel,1Roland Hellmann,1Laurent Truche,2Vladimir Roddatis,3Michel Mermoux,4Gaël Choblet,4Gabriel Tobie
Nature Astronomy 6, 554-559 Link to Article [DOI https://doi.org/10.1038/s41550-022-01613-2]
1Université Grenoble Alpes, CNRS, ISTerre, Grenoble, France
2GFZ German Research Centre for Geosciences, Potsdam, Germany
3Université Grenoble Alpes, Université Savoie Mont Blanc, CNRS, Grenoble INP, LEPMI, Grenoble, France
4Nantes Université, Université Angers, Le Mans Université, CNRS, UMR 6112, Laboratoire de Planétologie et Géosciences, Nantes, France

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Effects of Formation Pathways and Bromide Incorporation on Jarosite Dissolution Rates: Implications for Mars

1,2Di-Sheng Zhou,1,2Xiao-Wen Yu,2,3Rui Chang,1,4,5Yu-Yan Sara Zhao,1,4Xiongyao Li,1,4Jianzhong Liu,3Honglei Lin,3,6Chao Qi
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2022JE007202]
1Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
2University of Chinese Academy of Sciences, Beijing, China
3Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
4CAS Center for Excellence in Comparative Planetology, Hefei, China
5International Center for Planetary Science, College of Geosciences, Chengdu University of Technology, Chengdu, China
6College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, China
Published by arrangement with John Wiley & Sons

The dissolution rates of jarosite can constrain the duration of aqueous activities on Mars. To date, few studies have considered the influences of formation pathways and anion substitutions on jarosite dissolution rates. Here, we investigated how the formation pathways (Fe(II)-oxidation and Fe(III)-forced hydrolysis) and incorporation of bromide influence the dissolution rates of K-jarosite under eight aqueous conditions combining T (277 K, 298 K, and 323 K) and αw (0.35, 0.75 and 1), except for 277 K−0.35αw. The results show that jarosite dissolution rates are primarily influenced by aqueous T-αw conditions. Formation pathways and Br contents are secondary factors and only become notable under low T (277 K) and low αw (0.35) conditions. Taking the jarosite formation pathways and Br incorporation into account, the maximum lifetime of jarosite may be slightly longer than that of the halogen-free counterparts formed via Fe(III)-forced hydrolysis. Jarosite of the Burns Formation (Meridiani Planum) and the Pahrump Hills member (Gale Crater) are likely formed via Fe(II)-oxidation and halogen-bearing. Their estimated field lifetime (∼150 μm–1 mm particles) in low-T groundwater may last for hundreds of thousand years to a few million years. Jarosite in the Vera Rubin Ridge would share a similar lifespan if low-T solutions account for jarosite formation and subsequent interactions; otherwise, interactions with hydrothermal fluids (∼100°C) would substantially shorten the jarosite lifetime. We conclude that Martian jarosite may survive continuous aqueous interactions for up to a few million years, indicating an extended duration of aqueous environments than previously thought.

Low-lying resonances in Si 26 relevant for the determination of the astrophysical Al 25 (p,γ) Si 26 reaction rate

1,2Perello, J.F. et al. (>10)
Physical Review C 105, 035805 Link to Article [DOI 10.1103/PhysRevC.105.035805]
1Department of Physics, Florida State University, Tallahassee, 32306, FL, United States
2Intelligence and Space Research Division, Los Alamos National Laboratory, Los Alamos, 87545, NM, United States

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

High-precision measurements of Mo isotopes by N-TIMS

1Yobregat, Elsa,1Fitoussi, Caroline,2Pili, Eric,1Touboul, Mathieu
International Journal of Mass Spectrometry 476, 116846 Link to Article [DOI 10.1016/j.ijms.2022.116846]
1Laboratoire de Géologie de Lyon (LGL-TPE), CNRS UMR 5276, Univ. Lyon, UCBL, ENS de Lyon, 46 allée d’Italie, 69364, Lyon Cedex 7, France
2CEA, DAM, DIF, Arpajon, F-91297, France

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Sulfides and hollows formed on Mercury’s surface by reactions with reducing S-rich gases

1C.J.Renggli,1S.Klemme,2A.Morlok,1J.Berndt,2I.Weber,2H.Hiesinger,3P.L.King
Earth and Planetary Science Letters 593, 117647 Link to Article [https://doi.org/10.1016/j.epsl.2022.117647]
1Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Münster, 48149, Germany
2Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Münster, 48149, Germany
3Research School of Earth Sciences, The Australian National University, Canberra, 2601, Australia
Copyright Elsevier

The surface of Mercury is enriched in sulfur, with up to 4 wt.% detected by the NASA MESSENGER mission, and has been challenging to understand in the context of other terrestrial planets. We posit, that magmatic S was mobilized as a gas phase in volcanic and impact processes near the surface, exposing silicates to a hot S-rich gas at reducing conditions and allowing conditions for rapid gas-solid reactions. Here, we present novel experiments on the reaction of Mercury composition glasses with reduced S-rich gas, forming Ca- and Mg-sulfides. The reaction products provide porous and fragile materials that create previously enigmatic hollows on Mercury. Our model predicts that the gas-solid reaction forms Ca-Mg-Fe-Ti-sulfide assemblages with SiO2 and aluminosilicates, distinct from formation as magmatic minerals. The ESA/JAXA BepiColombo mission to Mercury will allow this hypothesis to be tested.

The effects of target density, porosity, and friction on impact crater morphometry: Exploratory experimentation using various granular materials

1Christopher J. Cline II,2Mark J. Cintala
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13886]
1Jacobs Technology, NASA Johnson Space Center, Astromaterials Research and Exploration Science, Mail Code X13, 2101 NASA Parkway, Houston, Texas, 77058 USA
2NASA Johnson Space Center, Astromaterials Research and Exploration Science, Mail Code X13, 2101 NASA Parkway, Houston, Texas, 77058 USA
Published by arrangement with John Wiley & Sons

The dimensions of relatively small-scale impact craters are undoubtedly sensitive to the physical properties of the target. Studying gravity-controlled crater formation at the laboratory scale often relies on cohesionless, granular materials, which, by their nature, make it difficult to separate the individual contributions to this process from all of the relevant target properties. Here, we conduct a suite of impact experiments to isolate and evaluate the effects of density, porosity, and internal friction on impact crater morphometry. Each made from one of four different granular materials, targets were impacted vertically with 4.76 mm aluminum projectiles at an average speed of ~1.55 km s−1. Two different methods were used to load these materials into the target bucket (pouring and sieving), resulting in targets that varied in bulk density and internal friction. The experimental results indicate that depth–diameter ratios of the craters are largely influenced by the loading method of the target material and are sensitive to the friction and porosity of the targets. Sieved targets (relatively higher density, lower porosity, and higher friction angle) produce craters that are markedly shallower, have notably smaller volumes, and exhibit a flat-floored morphology, with some possessing small central mounds. Flat-floored craters are typically attributed to a strength-layered target; in these experiments, however, they were produced in cohesionless targets. This study demonstrates that a flat floor is not necessarily diagnostic of strength layering in a target and, in some instances, might be the consequence of greater shear strengths in granular materials with high coefficients of static friction.

The effects of superheating and cooling rate on olivine growth in chondritic liquid

Marion Auxerre, François Faure, and Delphine Lequin
Meteoritics & Plaentary Science (in Press)
Link to Article [https://doi.org/10.1111/maps.13830]
CNRS, CRPG, UMR 7358, 15 rue Notre Dame des Pauvres F-54501 Vandoeuvre-lès-Nancy France
Published by arrangement with John Wiley & Sons

Chondrules, the major constituent of chondrites, are millimeter-sized igneous objects resulting from the crystallization of silicate liquids produced by the partial or complete melting of chondritic precursors, whose exact nature remains disputed. Various chondrule textures are observed as a function of the extent of the initial melting event. Here, we report dynamic crystallization experiments performed with a broad range of cooling rates (2–750 °C h−1) from superliquidus or subliquidus initial conditions to demonstrate the control of nucleation on the final chondrule texture. Classical crypto-porphyritic, micro-porphyritic, and porphyritic olivine textures were reproduced in subliquidus experiments in which heterogeneous nucleation dominates. In contrast, we were unable to reproduce barred olivine textures, regardless of the cooling rates investigated from superliquidus conditions; instead, macro-porphyritic textures were systematically obtained at low cooling rates (<10 °C h−1). The small number and large size of crystals in the macro-porphyritic texture are consistent with the initial step of superheating and the presence of long embayments that indicate an initial episode of rapid growth due to delayed nucleation. Crystals then acquired polyhedral shapes during a subsequent episode of slow growth. When the growth rate is too slow to decrease the degree of supersaturation in the liquid, a new episode of rapid growth produces a new generation of melt inclusions.

Global Hydrogen Abundances on the Lunar Surface

David J. Lawrence1, Patrick N. Peplowski1, Jack T. Wilson1, and Richard C. Elphic2
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2022JE007197]
1Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland
2NASA Ames Spaceflight Center, Moffett Field, California
Published by arrangement with John Wiley & Sons

A global map of bulk hydrogen abundances on the Moon is presented. This map was generated using data from the Lunar Prospector Neutron Spectrometer. This map required corrections for variations due to rare-earth elements, and was calibrated to Apollo sample hydrogen abundances. Since neutron-derived measurements sample hydrogen content to a depth of tens of cm, these results provide complementary insights to those provided by studies using spectral reflectance data, which sample depths of order μm. Comparison of these abundances to Apollo sample values suggest that the samples reflect actual hydrogen content on the lunar surface, not dominantly from non-lunar contamination. The average lunar hydrogen abundance is 47 ppm with a systematic uncertainty of ∼10 ppm. This is consistent with bulk hydrogen from solar wind emplacement. A bulk hydrogen enhancement (50–68 ppm) has been identified at the Moon’s largest pyroclastic deposit (Aristarchus Plateau), which corroborates prior observations that hydrogen and/or water plays a role in lunar magmatic events. Global data show a correlation between hydrogen and evolved materials rich in incompatible trace elements (i.e., KREEP type rocks), with a hydrogen excess of 14–36 ppm in these materials. Based on this hydrogen enhancement, we estimate a lower-limit water abundance within urKREEP materials (i.e., the final ∼2% of the lunar magma ocean) of 320–820 ppm H2O. This observation implies that water played a role in the original magma-ocean formation and solidification with a lower-limit water content in the original lunar magma ocean of 7–16 ppm or higher.