¹S. M. R. Turner et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13748]
¹AstrobiologyOU, School of Environment, Earth and Ecosystem Sciences, The Open University, Milton Keynes, MK7 6AA UK
Published by arrangement with John Wiley & Sons

Data returned by NASA’s Mars Science Laboratory Curiosity rover showed evidence for abundant secondary materials, including Fe-oxides, phyllosilicates, and an amorphous component on and below Vera Rubin ridge in the Murray formation. We used equilibrium thermochemical modeling to test the hypothesis that altered sediments were deposited as detrital igneous grains and subsequently underwent diagenesis. Chemical compositions of the Murray formations’ altered components were calculated using data returned by the chemistry and mineralogy X-ray diffraction instrument and the alpha particle X-ray spectrometer on board Curiosity. Reaction of these alteration compositions with a CO2-poor and oxidizing dilute aqueous solution was modeled at 25–100 °C, with 10–50% Fe3+/Fetot of the host rock. The modeled alteration assemblages included abundant phyllosilicates and Fe-oxides at water-to-rock ratios >100. Modeled alteration abundances were directly comparable to observed abundances of hematite and clay minerals at a water-to-rock ratio of 10,000, for system temperatures of 50–100 °C with fluid pH ranging from 7.9 to 9.3. Modeling results suggest that the hematite–clay mineral assemblage is primarily the result of enhanced groundwater flow compared to the Sheepbed mudstone observed at Yellowknife Bay, and underwent further, localized alteration to produce the mineralogy observed by Curiosity.

¹Matthew C.Brennan,¹Rebecca A.Fischer,²Francis Nimmo,³David P.O’Brien
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.09.022]
¹Department of Earth and Planetary Sciences, Harvard University (20 Oxford Street, Cambridge, MA 02138, USA)
²Department of Earth and Planetary Sciences, University of California Santa Cruz (1156 High Street, Santa Cruz, CA 95064, USA)
³Planetary Science Institute (1700 East Fort Lowell, Tucson, AZ 85719-2395, USA)
Copyright Elsevier

Determining how and when Mars formed has been a long-standing challenge for planetary scientists. The size and orbit of Mars are difficult to reproduce in classical simulations of planetary accretion, and this has inspired models of inner solar system evolution that are tuned to produce Mars-like planets. However, such models are not always coupled to geochemical constraints. Analyses of Martian meteorites using the extinct hafnium–tungsten (Hf–W) radioisotopic system, which is sensitive to the timing of core formation, have indicated that the Martian core formed within a few million years of the start of the solar system itself. This has been interpreted to suggest that, unlike Earth’s protracted accretion, Mars grew to its modern size very rapidly. These arguments, however, generally rely on simplified growth histories for Mars. Here, we combine likely accretionary histories from a large number of N-body simulations with calculations of metal–silicate partitioning and Hf–W isotopic evolution during core formation to constrain the range of conditions that could have produced Mars.

We find that there is no strong correlation between the final masses or orbits of simulated Martian analogs and their 182W anomalies, and that it is readily possible to produce Mars-like Hf–W isotopic compositions for a variety of accretionary conditions. The Hf–W signature of Mars is very sensitive to the oxygen fugacity (fO2) of accreted material because the metal–silicate partitioning behavior of W is strongly dependent on redox conditions. The average fO2 of Martian building blocks must fall in the range of 1.3–1.6 log units below the iron–wüstite buffer to produce a Martian mantle with the observed Hf/W ratio. Other geochemical properties (such as sulfur content) also influence Martian 182W signatures, but the timing of accretion is a more important control. We find that while Mars must have accreted most of its mass within ∼5 million years of solar system formation to reproduce the Hf–W isotopic constraints, it may have continued growing afterwards for over 50 million years. There is a high probability of simultaneously matching the orbit, mass, and Hf–W signature of Mars even in cases of prolonged accretion if giant impactor cores were poorly equilibrated and merged directly with the proto-Martian core.

^1,3V. Cabedo,²J. Llorca,^3,4J. M. Trigo-Rodriguez,⁵A.Rimola
Astronomy & Astrophysics 160, 650 Link to Article [DOI https://doi.org/10.1051/0004-6361/202039991]
¹Astrophysics department, CEA/DRF/IRFU/DAp, Université Paris Saclay, UMR AIM, 91191 Gif-sur-Yvette, France
²Institut de Tècniques Energètiques and Departament d’Enginyeria Química, Universitat Politècnica de Catalunya, Barcelona, Catalonia, Spain
³Institute of Space Sciences (CSIC), Meteorites, Minor Bodies and Planetary Sciences Group, Campus UAB, Carrer de Can Magrans, s/n, 08193, Barcelona, Catalonia, Spain
⁴Institut d’Estudis Espacials de Catalunya (IEEC), Gran Capità, 2 – baix, 08034, Barcelona, Catalonia, Spain
⁵Departament de Química, Universitat Autònoma de Barcelona, 08193 Bellaterra, Catalonia, Spain

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¹V.E.Hamilton et al. (>10)
Astronomy & Astrophysics 650, A120 Link to Article [DOI https://doi.org/10.1051/0004-6361/202039728]
¹Southwest Research Institute, Boulder, CO, USA

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¹F Merlin et al. (>10)
Astronomy & Astrophysics 648, A88 Link to Article [DOI https://doi.org/10.1051/0004-6361/202140343]
¹LESIA, Observatoire de Paris, Université PSL, CNRS, Université de Paris, Sorbonne Université, 92195 Principal Cedex Meudon, France

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¹Zhen Tiana,²Tomáš Magna,³James M. D. Day,⁴Klaus Mezger,⁵Erik E. Scherer,¹Katharina Lodders,⁶Remco C. Hin,¹Piers Koefoed,¹Hannah Bloom,¹Kun Wanga
Proceedings of the National Academy of Sciences of the United States of America (PNAS) 118, e2101155118 Link to Article [https://doi.org/10.1073/pnas.2101155118]
¹Department of Earth and Planetary Sciences, McDonnell Center for the Space Sciences, Washington University in St. Louis, St. Louis, MO 63130;
²Section of Isotope Geochemistry and Geochronology, Czech Geological Survey, CZ-118 21 Prague, Czech Republic;
³Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093;
⁴Institut für Geologie, Universität Bern, 3012 Bern, Switzerland;
⁵Institut für Mineralogie, Universität Münster, D48149 Münster, Germany;
⁶Bristol Isotope Group, School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, United Kingdom

The abundances of water and highly to moderately volatile elements in planets are considered critical to mantle convection, surface evolution processes, and habitability. From the first flyby space probes to the more recent “Perseverance” and “Tianwen-1” missions, “follow the water,” and, more broadly, “volatiles,” has been one of the key themes of martian exploration. Ratios of volatiles relative to refractory elements (e.g., K/Th, Rb/Sr) are consistent with a higher volatile content for Mars than for Earth, despite the contrasting present-day surface conditions of those bodies. This study presents K isotope data from a spectrum of martian lithologies as an isotopic tracer for comparing the inventories of highly and moderately volatile elements and compounds of planetary bodies. Here, we show that meteorites from Mars have systematically heavier K isotopic compositions than the bulk silicate Earth, implying a greater loss of K from Mars than from Earth. The average “bulk silicate” δ⁴¹K values of Earth, Moon, Mars, and the asteroid 4-Vesta correlate with surface gravity, the Mn/Na “volatility” ratio, and most notably, bulk planet H₂O abundance. These relationships indicate that planetary volatile abundances result from variable volatile loss during accretionary growth in which larger mass bodies preferentially retain volatile elements over lower mass objects. There is likely a threshold on the size requirements of rocky (exo)planets to retain enough H₂O to enable habitability and plate tectonics, with mass exceeding that of Mars.

^1,2,3Xiaohui Fu,¹Haijun Cao,¹Jian Chen,¹Xuting Hou,^1,3Zongcheng Ling,⁴Lin Xu,⁴Yongliao Zou,²Chipui Tang,^3,5Weibiao Hsu
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13743]
¹Shandong Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, Shandong, 264209 China
²State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Taipa, Macau, China
³CAS Center for Excellence in Comparative Planetology, Purple Mountain Observatory, Nanjing, 210034 China
⁴State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing, 100190 China
⁵CAS Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Nanjing, 210034 China
Published by arrangement with John Wiley & Sons

We performed a petrological, mineralogical, and geochemical study of the lunar feldspathic meteorite Northwest Africa (NWA) 11111. This meteorite contains several types of lithic clasts, including feldspathic clasts, mafic-rich clasts, granulites, impact melt breccias, minor basaltic clasts, and highly evolved clasts cemented in a recrystallized fine grain matrix. Both mineral chemistry and geochemical characteristics indicate a lunar origin for NWA 11111. The bulk analysis suggests that NWA 11111 is a typical feldspathic lunar meteorite, which is consistent with its large population of anorthositic clasts and plagioclase fragments. A comparison of geochemical data made by lunar orbiter missions indicates that this meteorite was likely launched from the Feldspathic Highland Terrane on the lunar farside. The chemical zoning, coupled with extensive exsolution lamellae (up to 20 μm in width) occurring in pyroxene across three sections of NWA 11111, demonstrates that this meteorite contains components derived from the surface to about 10 km of lunar crust. Magnesian anorthosite clasts are commonly present in the meteorite, indicating that magnesian anorthosite probably represents an important lithology in the lunar farside crust. Basaltic clasts in NWA 11111 range from a very low-Ti to a low-Ti mare basalt, possibly representing cryptomare on the lunar farside. Although a KREEPy signature for NWA 11111 is not evident, highly evolved clasts containing various silica polymorphs and/or K-feldspar are present. They may originate from late-stage residual liquids. Lithic clasts and mineral fragments within NWA 11111 provide new insights into the diversity of lunar crust lithology and magmatic processes on the lunar farside. This meteorite also offers rocky materials from a wide vertical section of lunar crust.

¹Daiki Yamamoto,²Noriyuki Kawasaki,^1,3Shogo Tachibana,³Michiru Kamibayashi,²Hisayoshi Yurimoto
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.09.016]
¹Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa 252-5210, Japan
²Department of Natural History Sciences, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan
³UTokyo Organization for Planetary Space Science, The University of Tokyo, Hongo, Tokyo 113-0033, Japan
Copyright Elsevier

Calcium-aluminum-rich inclusions (CAIs) are known as the oldest high-temperature mineral assemblages of the Solar System. The CAIs record thermal events that occurred during the earliest epochs of the Solar System formation in the form of heterogeneous oxygen isotopic distributions between and within their constituent minerals. Here, we explored the kinetics of oxygen isotope exchange during partial melting events of CAIs by conducting oxygen isotope exchange experiments between type B CAI-like silicate melt and 18O-enriched water vapor (PH2O = 5 × 10–2 Pa) at 1420°C. We found that the oxygen isotope exchange between CAI melt and water vapor proceeds at competing rates with surface isotope exchange and self-diffusion of oxygen in the melt under the experimental conditions. The 18O concentration profiles were well fitted with the three-dimensional spherical diffusion model with a time-dependent surface concentration. We determined the self-diffusion coefficient of oxygen to be ∼1.62 × 10–11 m2 s–1, and the oxygen isotope exchange efficiency on the melt surface was found to be ∼0.28 in colliding water molecules. These kinetic parameters suggest that oxygen isotope exchange rate between cm-sized CAI melt droplets and water vapor is dominantly controlled by the supply of water molecules to the melt surface at PH2O <∼10–2 Pa and by self-diffusion of oxygen in the melt at PH2O >∼1 Pa at temperatures above the melilite liquidus (1420–1540°C). To form type B CAIs containing 16O-poor melilite by oxygen isotope exchange between CAI melt and disk water vapor, the CAIs should have been heated for at least a few days at PH2O >10–2 Pa above temperatures of the melilite liquidus in the protosolar disk. The larger timescale of oxygen isotopic equilibrium between CAI melt and H2O compared to that between H2O and CO in the gas phase suggests that the bulk oxygen isotopic compositions of ambient gas at ∼1400°C in the type B CAI-forming region is preserved in the oxygen isotopic compositions of type B CAI melilite. Based on the observed oxygen isotopic composition, we suggest that a typical type B1 CAI (TS34) from Allende was cooled at a rate of ∼0.1–0.5 K h–1 during fassaite crystallization.

^1,2,4Zs Kapui,^2,3A.Kereszturi,⁴S.Józsa,⁵Cs Király,⁵Z.Szalai
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2021.105338]
¹Institute for Geological and Geochemical Research, Research Centre for Astronomy and Earth Sciences, Hungary
²Konkoly Thege Miklós Astronomical Institute, Research Centre for Astronomy and Earth Sciences, Konkoly Observatory, Hungary
³European Astrobiology Institute, Strasbourg, France
⁴Eötvös Loránd University, Department of Petrology and Geology, Hungary
⁵Geographical Institute, Research Centre for Astronomy and Earth Sciences, Hungary

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¹M.S.Fernanders et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114715]
¹Cooperative Institute for Research in Environmental Sciences and Department of Chemistry, University of Colorado, Boulder, CO, USA
Copyright Elsevier

Chlorine is ubiquitous on Mars, some of it in the form of oxy-chlorine salts. Chlorine-containing salts have been found at several landing sites, including that of Phoenix and Curiosity, in the form of perchlorates and chlorides. Several intermediate states also exist, of which chlorate is the most stable. While perchlorates have received much attention in the past few years, chlorate salts are much less studied. The ratio of perchlorate to chlorate on Mars is not well-defined but may be approximately 1:1. Chlorate salts have similar properties to perchlorates: high solubility, low eutectic temperatures, and likely low deliquescence relative humidities. Laboratory studies were performed to determine the ability of sodium and magnesium chlorate salts to take up water vapor at low temperatures (296 K to 237 K). These studies were performed using a Raman microscope equipped with an environmental chamber and a single particle optical levitator equipped with a Raman spectrometer. The deliquescence of sodium chlorate (NaClO3) was found to be temperature-dependent with the average relative humidity (RH) values ranging from 68% RH at 296 K to 80% RH at 237 K. Additionally, there was a slight deviation between experimental deliquescence values for this salt and those predicted by equilibrium thermodynamics. The observed efflorescence (recrystallization) of NaClO3 occurred at lower RH values ranging from 18% RH at 264 K to 24% RH at 249 K, demonstrating the hysteresis common to salt recrystallization. Several experiments were performed below the reported eutectic temperature of NaClO3 which resulted in supercooling of the brine and depositional ice nucleation. Based on the supercooling effects observed during our experiments, a revised metastable eutectic temperature of 237 K is suggested for NaClO3 compared to the previously reported value of 252 K. Two phases of magnesium chlorate (Mg(ClO3)2) were observed and exhibited different water uptake behavior. The most common form of Mg(ClO3)2 appeared to be a hydrated, amorphous phase, Mg(ClO3)2 • X H2O(a) that continuously took up water when the RH was increased. This water uptake behavior was even observed at very low humidity values, 5.0 (±1.9)% RH, with little temperature dependence. This detectable water persisted down to RH values close to 0%, averaging 0.5 (±0.6)% RH with no visible temperature dependence. The deliquescence relative humidity (DRH) of the hexahydrate, Mg(ClO3)2 • 6 H2O, was found to range from 50.9 (± 7.5)% at 227 K to 55.8 (± 6.6)% at 224 K and was consistent with thermodynamic calculations. Under conditions measured by the Remote Environmental Monitoring Station (REMS) instrument at Gale Crater and conditions modeled in the shallow subsurface, magnesium chlorate, if present, likely interacts with water vapor during some diurnal cycles.