¹Emma R. Stoutenburg,^2,3Razvan Caracas,⁴Natalia V. Solomatova,¹Andrew J. Campbell
Journal of Geophysical Research (Planets) (in Press) Open Access Link to Article [https://doi.org/10.1029/2024JE008525]
¹Department of the Geophysical Sciences, University of Chicago, Chicago, IL, USA
²Université Paris Cité, Institut de Physique du Globe de Paris, CNRS, Paris, France
³The Center for Planetary Habitability (PHAB), University of Oslo, Oslo, Norway
⁴Laboratoire de Géologie de Lyon LGLTPE UMR5276, CNRS, Ecole Normale Supérieure de Lyon, Centre Blaise Pascal, Lyon, France
Published by arrangement with John Wiley & Sons

Iron hydrides are a potentially dominant component of the metallic cores of planets, primarily because of hydrogen’s ubiquity in the universe and affinity for iron. Using ab initio molecular dynamics, we examine iron hydrides with 0.1, 0.33, 0.5, and 0.6 mol fraction hydrogen up to 100 GPa between 3,000 and 5,000 K to describe how hydrogen content affects the melt structure, hydrogen speciation, equation of state (EOS), atomic diffusivity, and melt viscosity. We find that the addition of hydrogen decreases the average Fe–Fe coordination number and lengthens Fe–Fe bonds, while Fe–H coordination number increases. The pair distribution function of hydrogen at low pressure indicates the presence of molecular hydrogen. By tracking chemical speciation, we show that the amount of molecular hydrogen increases and the number of iron in Hx≥1Fey≥0 clusters decreases as the hydrogen concentration increases. We parameterize a pressure, volume, temperature, and composition EOS and show that the molar volume and Grüneisen parameter of the melts decrease while the compressibility and thermal expansivity increase as a function of hydrogen concentration. We find that hydrogen acts as a lubricant in the melts as the iron and hydrogen become more diffusive and the melts become more inviscid as the hydrogen concentration increases. We estimate 2.7 wt% hydrogen in the Martian core and 0.49–1.1 wt% hydrogen in Earth’s outer core based on comparisons to seismic models, with the assumption that the cores are pure liquid iron-hydrogen alloy, and we compare the small exoplanet population with mass-radius curves of iron hydride planets.

^1,2S.J. vanBommel et al. (>10)
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2024.116355]
¹McDonnell Center for the Space Sciences, Washington University in St. Louis, St. Louis, MO, USA
²Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO, USA
Copyright Elsevier

The “Planetary Instrument for X-ray Lithochemistry” (PIXL) X-ray spectrometer conducts in situ geochemical analyses of martian rocks and regolith interrogated by the Mars 2020 rover, Perseverance. In addition to quantifying primary rock-forming elements, PIXL can quantify trace elements that in turn can provide additional constraints on the geologic history of Mars. Accurate quantifications of trace elements can require additional analytical techniques to mitigate experimental, background, and crystalline effects within PIXL spectra. In this study, we focus on reducing the impact of these effects and investigate the potential presence of rare earth elements (REEs). The study specifically investigates cerium given its typical relative abundance in many geologic materials compared to other REEs and its potential to mimic fluorescence features produced by organics under deep UV excitation. A detailed analysis of PIXL targets analyzed through the first 887 martian days of the Perseverance mission did not produce any conclusive Ce detections. Phosphorus-enriched materials analyzed by PIXL are estimated to contain sub-675 ppm Ce and sulfate-enriched materials sub-450 ppm Ce. The method presented can help constrain limits on the abundance of additional trace elements of interest that also face a similar analytical burden. PIXL’s potential to assess REE abundances, outside of yttrium, is limited for expected concentrations in surface materials. Determining most REE concentrations in materials interrogated by Perseverance will therefore likely require terrestrial analyses.

^1,2A. G. J. Jurewicz,³A. M. Amarsi,⁴D. S. Burnett,^5,6N. Grevesse
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14272]
¹School of Earth and Space Exploration, Arizona State University Busek Center for Meteorite Studies, Tempe, Arizona, USA
²Department of Earth Science, Dartmouth College, Hanover, New Hampshire, USA
³Theoretical Astrophysics, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden
⁴Department of Geology and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
⁵Centre Spatial de Liège, Université de Liège, Liège, Belgium
⁶STAR Institute, Université de Liège, Liège, Belgium
Published by arrangement with John Wiley & Sons

CI chondrites have been a proxy for the solar system since the mid-20th century. The photospheric and CI chondrite abundances (P and CI, respectively) show a strong correlation. CI as a proxy is also justified by the (i) smoothness of their abundances plotted as a function of odd mass number and (ii) agreement within the error of P as determined spectroscopically. But our statistical assessment of spectroscopic studies and solar wind from the Genesis mission indicates that the small, ~10%–30%, differences (residuals) between CI and P depend on the 50% condensation temperature (Tc50). So, if CI is to be used as a proxy for P, Cosmochemists may want to add a correction to individual elements. Our work is consistent with two published hypotheses: that (i) residuals are linear with Tc50 and (ii) that elements having Tc50 > 1343 K are depleted relative to those with 495 K < Tc50 < 1343 K in CI. We discuss other interpretations which are also feasible. Understanding these small differences of the CI and P for different elements and their variation with Tc50 can help constrain future models of solar system formation and the history of CI chondrites.

¹Liam S. T. McGovern, ¹Bruce L. A. Charlier, ¹Colin J. N. Wilson
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14278]
¹School of Geography, Environment and Earth Sciences, Victoria University of Wellington, Wellington, New Zealand
Published by arrangement with John Wiley & Sons

Stepwise acid leaching experiments were performed on the pre-rain CM2 fall Aguas Zarcas to interrogate release patterns and isolate fractions with isotopic anomalies. Acid leachates and a bulk sample were analyzed for elemental abundances via solution ICP-MS, and Sr and Ba isotopic compositions were measured using TIMS. Isotopic systematics reveal diverse values for the bulk sample and leachates, interpreted to reflect the Aguas Zarcas parent body history. Compared with the NBS987 standard, μ84Sr values for the bulk sample average + 90, while the leach fractions yield +326 to −2089, with the largest μ84Sr depletions in the strongest acid leachates. For Ba isotopes, the bulk sample shows resolvable depletions (μ values) in 130Ba (−210), 135Ba (−64), 137Ba (−73) and 138Ba (−89). Early leachates show positive anomalies in 130Ba (up to +2295), 132Ba, 135Ba, 137Ba, and 138Ba. In contrast, final leachates show strong depletions for the same nuclides (up to −60,000 ppm μ130Ba). The Sr and Ba isotopic anomalies found in the earlier leachates suggest that nucleosynthetic signatures were redistributed to more soluble phases during parent body alteration. Moreover, contrasting p-nuclide Sr and Ba nucleosynthetic anomalies suggest that presolar contributions came from a variety of nucleosynthetic sources, including possibly a rotating massive star undergoing a core-collapse supernova or an electron capture supernova.

¹Marie Kepp, ^1,2,3Lu Pan, ¹Jens Frydenvang, ¹Martin Bizzarro
Earth and Planetary Science Letters 648, 119082 Link to Article [https://doi.org/10.1016/j.epsl.2024.119082]
¹Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, Copenhagen, Denmark
²School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, PR China
³Deep Space Exploration Laboratory, Hefei 230026, PR China
Copyright Elsevier

The Mars Science Laboratory has been investigating the central mound of Gale crater since 2012 and revealed evidence of silica enrichment in several locations, suggesting that the geologic processes related to the formation of hydrated silica could be widespread. A reanalysis of orbital data over Aeolis Mons indicates the existence of an extensive unit rich in hydrated silica. These silica-enriched deposits, found at the base of Aeolis Mons, span elevations from -4513 m to -3351 m. The mapped hydrated silica deposits are spatially adjacent to an erosion-resistant capping unit, previously mapped as the mound skirting unit, which lies beneath the terminal deposits from local canyons and valleys. We hypothesize that the hydrated silica-bearing unit precipitated from groundwater which migrated upwards or deposited as a volcaniclastic silica-rich layer which was rehydrated during the late-stage canyon and valley forming events. The silica-bearing unit beneath the capping unit is protected against erosion by younger fan-shaped deposits and became exposed only recently. The mineralogy and stratigraphic relations with Mount Sharp units imply that the aqueous activities leading to silica diagenesis were likely a basin-wide process that occurred long after the formation of lakes in Gale crater’s geological history and experienced limited water-rock interaction since then.

¹M. Brož,²P. Vernazza,^3,4M. Marsset,⁴F. E. DeMeo,⁴R. P. Binzel,¹D. Vokrouhlický,⁵D. Nesvorný
Nature 634, 566-571 Link to Article [DOI https://doi.org/10.1038/s41586-024-08006-7]
¹Charles University, Faculty of Mathematics and Physics, Institute of Astronomy, Prague, Czech Republic
²Aix Marseille University, CNRS, CNES, LAM, Institut Origines, Marseille, France
³European Southern Observatory (ESO), Santiago, Chile
⁴Department of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA, USA
⁵Department of Space Studies, Southwest Research Institute, Boulder, CO, USA

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

^1,2M.Marsset et al. (>10)
Nature 634, 561-565 Link to Article [DOI https://doi.org/10.1038/s41586-024-08007-6]
¹European Southern Observatory (ESO), Santiago, Chile
²Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA

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

¹David G. Burtt et al. (>10)
Proceedings of the National Academy of Sciences of the United States of America (PNAS) 121, e2321342121 Open Access Link to Article [https://doi.org/10.1073/pnas.232134212]
¹NASA Postdoctoral Fellow, Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771

Carbonate minerals are of particular interest in paleoenvironmental research as they are an integral part of the carbon and water cycles, both of which are relevant to habitability. Given that these cycles are less constrained on Mars than they are on Earth, the identification of carbonates has been a point of emphasis for rover missions. Here, we present carbon (δ13C) and oxygen (δ18O) isotope data from four carbonates encountered by the Curiosity rover within the Gale crater. The carbon isotope values range from 72 ± 2‰ to 110 ± 3‰ Vienna Pee Dee Belemnite while the oxygen isotope values span from 59 ± 4‰ to 91 ± 4‰ Vienna Standard Mean Ocean Water (1 SE uncertainties). Notably, these values are isotopically heavy (13C- and 18O-enriched) relative to nearly every other Martian material. The extreme isotopic difference between the carbonates and other carbon- and oxygen-rich reservoirs on Mars cannot be reconciled by standard equilibrium carbonate–CO2 fractionation, thus requiring an alternative process during or prior to carbonate formation. This paper explores two processes capable of contributing to the isotopic enrichments: 1) evaporative-driven Rayleigh distillation and 2) kinetic isotope effects related to cryogenic precipitation. In isolation, each process cannot reproduce the observed carbonate isotope values; however, a combination of these processes represents the most likely source for the extreme isotopic enrichments.

^1,2Bohao Chen,^2,3Xiao-Wen Yu,^4,5Yu-Yan Sara Zhao,^2,3Di-Sheng Zhou,^2,3Shuai-Yi Qu,^1,6Jiannan Zhao,^3,7Chao Qi,^2,5Xiongyao Li,^2,5Jianzhong Liu
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2023JE008250]
¹State Key Laboratory of Geological Process and Mineral Resources, Planetary Science Institute, School of Earth Sciences, China University of Geosciences, Wuhan, China
²Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
³College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, China
⁴Research Center for Planetary Science, College of Earth and Planetary Sciences, Chengdu University of Technology, Chengdu, China
⁵CAS Center for Excellence in Comparative Planetology, Hefei, China
⁶Key Laboratory of Geological Survey and Evaluation of Ministry of Education, China University of Geosciences, Wuhan, China
⁷Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
Published by arrangement with John Wiley & Sons

The scarce carbonate record on the Martian surface is one of the fundamental unsolved issues for paleoclimate and environmental evolution. Whether carbonates first formed and then dissolved due to a transition in global environments or whether Mg–Fe carbonates never extensively formed due to geochemical kinetics thresholds remains unknown. In this study, we experimentally examined the preservation potential of siderite in Mars-relevant fluids, including ultrapure water, H2O2, NaClO4, NaClO3, NaCl, Na2SO4, NaHCO3, and Na2SiO3 solutions, at 277 K. The effects of the water/rock ratio at WR10 and WR100 on dissolution rates were also investigated. We found that siderite dissolution and subsequent oxidation and hydrolysis of leached Fe did not substantially acidify the solutions. The siderite dissolved relatively rapidly in the chloride and chlorate solutions and slowly in the silica or bicarbonate solutions. In a circum-neutral to slightly alkaline aqueous environment with oxidative species, the mobility of leached Fe was limited, leading to the formation of goethite or lepidocrocite, which clustered on the siderite surface. The longest lifetime of 1-mm siderite grains was found in the Na2SiO3 solution at WR100, which was estimated to range from 198 ka to 198 Ma. Water-limited, silica-rich, and oxidative aqueous environments benefit siderite preservation on the Martian surface. Our results support that the lack of voluminous siderite on Mars may be primarily due to the inhibition of its formation rather than alteration and dissolution after its presence, consistent with the recent detection of Mg–Fe carbonate at Gale Crater and Jezero Crater.

¹K. H. Joy,²N. Wang,¹J. F. Snape,¹A. Goodwin,¹J. F. Pernet-Fisher,³M. J. Whitehouse,²Y. Liu,²Y. T. Lin,⁴J. R. Darling,⁵P. Tar,¹R. Tartèse
Nature Astronomy (in Press) Open Access Link to Article [DOI https://doi.org/10.1038/s41550-024-02380-y]
¹Department of Earth and Environmental Sciences, The University of Manchester, Manchester, UK
²Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
³Department of Geosciences, Swedish Museum of Natural History, Stockholm, Sweden
⁴School of the Environment, Geography and Geosciences, University of Portsmouth, Portsmouth, UK
⁵Previously at the School of Health Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK

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