¹A. A. Simon,¹H. H. Kaplan,²E. Cloutis,³V. E. Hamilton,⁴C. Lantz,¹D. C. Reuter,⁵D. Trang,^6,7S. Fornasier,⁸B. E. Clark,⁹D. S. Lauretta
Astronomy & Astrophysics 644, A148 Link to Article [DOI https://doi.org/10.1051/0004-6361/202039688]
¹Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA
²Department of Geography, University of Winnipeg, Winnipeg, Canada
³Southwest Research Institute, Boulder, CO, USA
⁴Institut d’Astrophysique Spatiale, Université Paris-Saclay, CNRS, 91405 Orsay, France
⁵Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Manoa, Honolulu, HI, USA
⁶LESIA, Observatoire de Paris, Université PSL, CNRS, Université de Paris, Sorbonne Université, 5 place Jules Janssen, 92195 Meudon, France
⁷Institut Universitaire de France (IUF), 1 rue Descartes, 75231 Paris Cedex 05, France
⁸Department of Physics and Astronomy, Ithaca College, Ithaca, NY, USA
⁹Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA

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^1,2S.Fornasier et al. (>10)
Astronomy & Astrophysics 644, A142 Link to Article [DOI https://doi.org/10.1051/0004-6361/202039552]
¹LESIA, Observatoire de Paris, Université PSL, CNRS, Université de Paris, Sorbonne Université, 5 place Jules Janssen, 92195 Meudon, France
²Institut Universitaire de France (IUF), 1 rue Descartes, 75231 Paris Cedex 05, France

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¹Conel M.O’D. Alexander,^1,2Jonathan G. Wynn,¹Roxane Bowden
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13746]
¹Earth and Planets Laboratory, Carnegie Institution for Science, 5241 Broad Branch Road, NW, Washington, District of Columbia, 20015 USA
²Division of Earth Sciences, National Science Foundation, 2415 Eisenhower Avenue, Alexandria, Virginia, 22314 USA
Published by arrangement with John Wiley & Sons

The bulk S elemental abundances and δ34S values for 83 carbonaceous chondrites (mostly CMs and CRs) and Semarkona (LL3.0) are reported. In addition, the S elemental abundances and δ34S values of insoluble organic material (IOM) isolated from 25 carbonaceous chondrites (CMs, CRs, and three ungrouped) are presented. The IOM only contributes 2–7% of the S to the bulk meteorites analyzed and exhibits no systematic variations. The average group bulk S abundances are similar to previous measurements. In-group variations likely reflect variations in matrix abundances, as well as parent body processes and weathering. The S and C abundances are roughly correlated and scatter about a mixing line between CI-like matrix and C-free and S-depleted chondrules. Systematic deviations from this mixing line may indicate different degrees of heating of matrix material in the nebula. There are no systematic variations in average group δ34S values, in contrast to what is seen for the volatile chalcophiles Zn, Te, Se, and Ag, as well as the less volatile siderophile Cu. Renormalization of the elemental and isotopic compositions indicates that the elemental and isotopic fractionations of Zn, Te, and Ag were controlled by the same process, whereas Se is intermediate in its behavior between these three elements and S. The isotopic fractionations could be associated with diffusion of volatile chalcophiles into sulfide at the end of chondrule formation. Copper appears to be distinct in its behavior from the chalcophiles, perhaps because it is more refractory and more siderophile.

¹Logan Jaeger et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13747]
¹Space Sciences Laboratory, University of California at Berkeley, Berkeley, California, 94720 USA
Published by arrangement with John Wiley & Sons

NASA’s Stardust mission utilized a sample collector composed of aerogel and aluminum foil to return cometary and interstellar particles to Earth. Analysis of the aluminum foil begins with locating craters produced by hypervelocity impacts of cometary and interstellar dust. Interstellar dust craters are typically less than one micrometer in size and are sparsely distributed, making them difficult to find. In this paper, we describe a convolutional neural network based on the VGG16 architecture that achieves high specificity and sensitivity in locating impact craters in the Stardust interstellar collector foils. We evaluate its implications for current and future analyses of Stardust samples.

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.