¹Jitse Alsemgeest,¹Fraukje M. Brouwer,²Luis F. Auqué,³Natalia Hauser,³Wolf Uwe Reimold
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13763]
¹Geology and Geochemistry Cluster, Faculty of Science, Vrije Universiteit, De Boelelaan 1085, Amsterdam, 1081HV The Netherlands
²Department of Geosciences, University of Zaragoza, Calle Pedro Cerbuna 12, Zaragoza, 50009 Spain
³Laboratory of Geochronology and Isotope Geochemistry, Geosciences Institute, University of Brasília, Brasília, DF, CEP 70910-900 Brazil
Published by arrangement with John Wiley & Sons

Hydrothermal systems provide a possible habitat for early life and are key targets in the quest for life outside Earth. In impact craters on Mars, hydrous minerals can represent products of impact-generated hydrothermal systems (IGHS) or minerals already present in the crust and exposed during impact-caused excavation. Because of its basaltic target rock, similar in composition to Martian crust, the Vista Alegre impact structure in Brazil is one of the very few analog structures that may reveal the origin of these minerals, if evidence of hydrothermal alteration is established. This work presents the results of a systematic search for evidence of hydrothermal alteration at the Vista Alegre impact structure. Four types of alteration were identified, all within a 2.5–3.0 km radius from the crater center: a zircon-bearing melt veinlet, two sets of hydrothermal veins consisting predominantly of calcite and chabazite, and local alteration comprising saponite. Thermodynamic modeling suggests subsequent heating and cooling for each of the hydrothermal vein sets. Combined thermodynamic and spectrometric evidence indicates that development of a vigorous IGHS is unlikely. If similar processes occur on Mars, hydrous minerals are more likely preimpact phases exposed by excavation, rather than being formed through an IGHS.

^1,2Connor D.Hilton,¹Richard D.Ash,¹Richard J.Walker
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.11.035]
¹Department of Geology, University of Maryland, College Park, Maryland, 20742, USA
²Present address: Environmental Signatures Team, Pacific Northwest National Laboratory, Richland, Washington, 99354, USA
Copyright Elsevier

The projected relative abundances of the highly siderophile elements (HSE; Re, Os, Ir, Ru, Pt, and Pd) for bulk parent bodies of 10 magmatic iron meteorite groups/grouplet (IC, IIAB, IIC, IID, IIF, IIIAB, IIIF, IVA, IVB, and South Byron Trio) are broadly similar and show no resolvable differences between noncarbonaceous (NC) and carbonaceous (CC) genetic heritage. The processes driving genetic isotopic heterogeneity in the early Solar System, therefore, evidently did not leave discernable chemical fingerprints with respect to HSE relative abundances on the bulk planetesimal scale. By contrast, the absolute abundances of HSE projected for parent body cores, which reflect core size, are more variable and, on average, higher in CC bodies compared to NC bodies. Overall, bulk core chemical compositions, as well as core size, are linked to the distribution of Fe within a parent body, which is controlled by its oxidation state. The CC parent bodies are constrained to have formed under heterogeneous oxidizing conditions which were, on average, more oxidizing than those of the NC environment.

¹Heng-Ci Tian et al. (>10)
Nature 600, 59-63 Link to Article [DOI https://doi.org/10.1038/s41586-021-04119-5]
¹Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China

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

¹Qiu-Li Li et al. (>10)
Nature 600, 54-58 Link to Article [DOI https://doi.org/10.1038/s41586-021-04100-2]
¹State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China

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

¹Sen Hu et al. (>10)
Nature 600, 49-53 Link to Article [DOI https://doi.org/10.1038/s41586-021-04107-9]
¹Key Laboratory of the Earth and Planetary Physics, Chinese Academy of Sciences, Beijing, China

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

¹Nathalie Turenne,¹Alexis Parkinson,¹Daniel M.Applin,¹Paul Mann,¹Edward A.Cloutisa,²Stanley A.Mertzman
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2021.105377]
¹Centre for Terrestrial and Planetary Exploration, University of Winnipeg, Winnipeg, Manitob, R3B 2E9, Canada
²Department of Earth and Environment, Franklin and Marshall College, P.O. Box 3003, Lancaster, PA, 17604, 3003, USA

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

¹I.Mitrofanov,¹A.Malakhov,¹M.Djachkova,¹D.Golovin,¹M.Litvak,¹M.Mokrousov,¹A.Sanin,²H.Svedhem,¹L.Zelenyi
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114805]
¹Space Research Institute of the Russian Academy of Sciences, Profsoyuznaya str. 84/32, 117997 Moscow, Russia
²European Space Agency, ESTEC, Keplerlaan 1, 2201 AZ Noordwijk, Netherlands
Copyright Elsevier

Studies of hydrogen deposition in the shallow Martian subsurface have been conducted by two neutron and one gamma-ray detectors in the past and provided global hydrogen maps (Boynton et al., 2002; Feldman et al., 2002; Mitrofanov et al., 2002). It is known from these maps that hydrogen is most abundant in the polar permafrost areas compared to the equatorial band where frozen water is not stable on the surface. However, the spatial resolution of hundreds of kilometres typical for these maps does not allow for detection of local hydrogen-rich features that can be associated with geological structures. FREND neutron telescope (Mitrofanov et al., 2018) onboard ExoMars TGO (Vago et al., 2015) is capable of a much better spatial resolution for mapping neutron emission of Mars. In this Report we present the analysis of the most intriguing local area of highly suppressed neutron emission in the vicinity of the Martian equator, which coincides with Candor Chaos in the central area of Valles Marineris, thought to be promising for testing water ice (Gourronc et al., 2014). Provided such suppression would be interpreted as the evidence for very high content of hydrogen in the soil, the mean water equivalent hydrogen value in the local suppression area should be as large as 40.3 wt%. This finding is thought to be uncommon for equatorial regions, but is probably associated with particular geomorphological conditions inside Valles Marineris.

¹Max Collinet,¹Ana-Catalina Plesa,²Timothy L. Grove,¹Sabrina Schwinger,^3,1Thomas Ruedas,¹Doris Breuer
Journal of Geophysical Research (Planets) (In Press) Link to Article [https://doi.org/10.1029/2021JE006985]
¹German Aerospace Center (DLR), Institute of Planetary Research, Rutherfordstraße 2, 12 489 Berlin Germany
²Massachusetts Institute of Technology, Department of Earth, Atmospheric and Planetary Sciences, 77 Massachusetts Avenue, MA, 02 139 USA
³Museum für Naturkunde Berlin, Impact and Meteorite Research, Invalidenstraße 43, 10 115 Berlin Germany
Published by arrangement with John Wiley & Sons

Martian basalts identified by rover in-situ analyses and the study of meteorites represent a direct link to the melting process in the planet’s interior and can be used to reconstruct the composition of the mantle and estimate its temperature. Experimentally calibrated numerical models are powerful tools to systematically search for the mantle compositions and melting conditions that can produce melts similar to primary basalts. However, currently available models are not suitable for modeling the melting of FeO-rich peridotites. In this study, we present experiments performed at 1.0 and 2.4–2.6 GPa on a primitive Martian mantle with various P2O5 contents. We use the new experiments together with a comprehensive database of previous melting experiments to calibrate a new model called MAGMARS. This model can reproduce the experimental melt compositions more accurately than Gibbs free energy minimization software (e.g. pMELTS) and can simulate near-fractional polybaric melting of various mantle sources. In addition, we provide an updated thermobarometer that can estimate the P–T melting conditions of primary melts and can be used as a prior step to constrain the input parameters of the MAGMARS melting model. We apply MAGMARS to estimate the source composition of the Adirondack-class basalts and find that melting a depleted mantle, at 2.3–1.7 GPa (Tp=1390±40°C) can best explain their bulk composition and K2O/Na2O ratio. MAGMARS represents a fast and accurate alternative to calculate the composition of the Martian primary melts and can be used as a stand-alone package or integrated with geodynamical models or other independent modeling software.

¹L.B.Breitenfeld et al. (>10)
Journal of Geophysical research (Planets) (In Press) Link to Article [https://doi.org/10.1029/2021JE007035]
¹Department of Geosciences, Stony Brook University, Stony Brook, NY, USA
Published by arrangement with John Wiley & Sons

Planetary surfaces can be complex mixtures of coarse and fine particles that exhibit linear and nonlinear mixing behaviors at mid-infrared (MIR) wavelengths. Machine learning multivariate analysis can estimate modal mineralogy of mixtures and is favorable because it does not assume linear mixing across wavelengths. We used partial least squares (PLS) and least absolute shrinkage and selection operator (lasso), two types of machine learning, to build MIR spectral models to determine the surface mineralogy of the asteroid (101955) Bennu using OSIRIS-REx Thermal Emission Spectrometer (OTES) data. We find that PLS models outperform lasso models. The cross-validated root-mean-square error of our final PLS models (consisting of 317 unique spectra of samples derived from 13 analog mineral samples and eight meteorites) range from ∼4–13 vol% depending on the mineral group. PLS predictions in vol% of Bennu’s average global composition are 78% phyllosilicate, 9% olivine, 11% carbonates, and 6% magnetite. Pyroxene is not predicted for the global average spectrum, though it has been detected in small amounts on Bennu. These mineral abundances confirm previous findings that the composition of Bennu is consistent with CI/CM chondrites with high degrees of aqueous alteration. The predicted mineralogy of two previously identified OTES spectral types vary minimally from the global average. In agreement with previous work, we interpret OTES spectral differences as primarily caused by relative abundances of fine particulates rather than major compositional variations.

¹Megan D. Mouser,¹Nicholas Dygert,²Brendan A. Anzures,¹Nadine L. Grambling,³Rostislav Hrubiak,^4,5Yoshio Kono,³Guoyin Shen,²Stephen W. Parman
Journal of Geophysical Research (Planets) (In Press) Link to Article [https://doi.org/10.1029/2021JE006946]
¹Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN, USA
²Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI, USA
³HPCAT, X-ray Science Division, Argonne National Laboratory, Argonne, IL, USA
⁴Geophysical Laboratory, Carnegie Institution of Washington, Argonne, IL, USA
⁵Now at Geodynamics Research Center, Ehime University, Matsuyama, Japan
Published by arrangement with John Wiley & Sons

Mercury has a compositionally diverse surface that was produced by different periods of igneous activity suggesting heterogeneous mantle sources. Understanding the structure of Mercury’s mantle formed during the planet’s magma ocean stage could help in developing a petrologic model for Mercury, and thus, understanding its dynamic history in the context of crustal petrogenesis. We present results of falling sphere viscometry experiments on late-stage Mercurian magma ocean analogue compositions conducted at the Advanced Photon Source, beamline 16-BM-B, Argonne National Laboratory. Owing to the presence of sulfur on the surface of Mercury, two compositions were tested, one with sulfur and one without. The liquids have viscosities of 0.6–3.9 (sulfur-bearing; 2.6–6.2 GPa) and 0.6–10.9 Pa·s (sulfur-free; 3.2–4.5 GPa) at temperatures of 1600–2000°C. We present new viscosity models that enable extrapolation beyond the experimental conditions and evaluate grain growth and the potential for crystal entrainment in a cooling, convecting magma ocean. We consider scenarios with and without a graphite flotation crust, suggesting endmember outcomes for Mercury’s mantle structure. With a graphite flotation crust, crystallization of the mantle would be fractional with negatively buoyant minerals sinking to form a stratified cumulate pile according to the crystallization sequence. Without a flotation crust, crystals may remain entrained in the convecting liquid during solidification, producing a homogeneous mantle. In the context of these endmember models, the surface could result from dynamical stirring or mixing of a mantle that was initially heterogeneous, or potentially from different extents of melting of a homogeneous mantle.