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

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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

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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.

¹M. Lo,^1,2G. La Spina,¹K. H. Joy,¹M. Polacci,¹M. Burton
Journal of Geophysical Research (Planets) (In Press) Link to Article [https://doi.org/10.1029/2021JE006939]
¹Department of Earth and Environmental Sciences, University of Manchester, Manchester, UK
²Istituto Nazionale di Geofisica e Vulcanologia Sezione di, Catania, Sicilia, Italy
Published by arrangement with John Wiley & Sons

The Moon is not volcanically active at present, therefore, we rely on data from lunar samples, remote sensing, and numerical modeling to understand past lunar volcanism. The role of different volatile species in propelling lunar magma ascent and eruption remains unclear. We adapt a terrestrial magma ascent model for lunar magma ascent, considering different compositions of picritic magmas and various abundances of H₂, H₂O, and CO (measured and estimated) for these magmas. We also conduct a sensitivity analysis to investigate the relationship between selected input parameters (pre-eruptive pressure, temperature, conduit radius, and volatile content) and given outputs (exit gas volume fraction, velocity, pressure, and mass eruption rate). We find that, for the model simulations containing H₂O and CO, CO was more significant than H₂O in driving lunar magma ascent, for the range of volatile contents considered here. For the simulations containing H₂ and CO, H₂ had a similar or slightly greater control than CO on magma ascent dynamics. Our results showed that initial H₂ and CO content has a strong control on exit velocity and pressure, two factors that strongly influence the formation of an eruption plume, pyroclast ejection, and overall deposit morphology. Our results highlight the importance of (a) quantifying and determining the origin of CO, and (b) understanding the abundance of different H-species present within the lunar mantle. Quantifying the role of volatiles in driving lunar volcanism provides an important link between the interior volatile content of the Moon and the formation of volcanic deposits on the lunar surface.

¹Sylvain Piqueux,¹Tuan H. Vu,¹Jonathan Bapst,²Laurence A. J. Garvie,¹Mathieu Choukroun,³Christopher S. Edwards
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2021JE007003]
¹Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
²Center for Meteorite Studies, Arizona State University, Tempe, AZ, USA
³Department of Astronomy and Planetary Sciences, Northern Arizona University, Flagstaff, AZ, USA
Published by arrangement with John Wiley & Sons

Specific heat capacity Cp(T) is an intrinsic regolith property controlling planetary surface temperatures along with the albedo, density, and thermal conductivity. Cp(T) depends on material composition and temperature. Generally, modelers assume a fixed specific heat capacity value, or a standard temperature dependence derived from lunar basalts, mainly because of limited composition-specific data at low temperatures relevant to planetary surfaces. In addition, Cp(T) only appears to vary by a small factor across various materials, in contrast with the bulk regolith thermal conductivity, which ranges over ∼3–4 orders of magnitude as a function of the regolith physical state (grain size, cementation, sintering, etc.). For these reasons, the impact of the basaltic assumption on modeled surface temperature is often considered unimportant although this assumption is not particularly well constrained. In this paper, we present specific heat capacity measurements and parameterizations from ∼90 to ∼290 K of 28 meteorites including those possibly originating from Mars and Vesta, and covering a wide range of planetary surface compositions. Planetary surface temperatures calculated using composition-specific Cp(T) are within urn:x-wiley:21699097:media:jgre21756:jgre21756-math-00012 K of model runs assuming a basaltic composition. This urn:x-wiley:21699097:media:jgre21756:jgre21756-math-00022 K range approaches or exceeds typical instrumental noise or other sources of modeling uncertainties. These results suggest that a basaltic assumption for Cp(T) is generally adequate for the thermal characterization of a wide range of planetary surfaces, but possibly inadequate when looking at leveraging subtle trends to constrain subsurface layering, roughness, or seasonal/diurnal volatile transfer.

¹Kovács A.,^2,3A.,Lewis L.H.,⁴Palanisamy D.,¹Denneulin T.,⁵Schwedt A.,⁶Scott E.R.D.,^4,7Gault B.,⁴Raabe D.,¹Dunin-Borkowski R.E.,⁸Charilaou M.
Nano Letters 21, 8135-8142 Link to Article [DOI 10.1021/acs.nanolett.1c02573]
¹Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Peter Grünberg Institute, Forschungszentrum Jülich GmbH, Jülich, 52425, Germany
²Department of Chemical Engineering, Northeastern University, Boston, 02115, MA, United States
³Department of Mechanical and Industrial Engineering, Northeastern University, Boston, 02115, MA, United States
⁴Max-Planck-Institut für Eisenforschung, Düsseldorf, 40237, Germany
⁵Central Facility for Electron Microscopy, RWTH Aachen University, Aachen, 52074, Germany
⁶Hawaii Institute of Geophysics and Planetology, University of Hawaii, Honolulu, 96822, HI, United States
⁷Department of Materials, Royal School of Mines, Imperial College London, London, SW7 2BP, United Kingdom
⁸Department of Physics, University of Louisiana at Lafayette, Lafayette, 70504, LA, United States

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¹Otto, K.A. et al. (>10)
Planetary Science Journal 2, 188 Link to Article [DOI 10.3847/PSJ/ac034b]
¹German Aerospace Center, Institute of Planetary Research, Rutherfordstaße 2, Berlin, D-12489, Germany

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