Experimental Investigation of Mercury’s Magma Ocean Viscosity: Implications for the Formation of Mercury’s Cumulate Mantle, Its Subsequent Dynamic Evolution, and Crustal Petrogenesis

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.

Determining the Effect of Varying Magmatic Volatile Content on Lunar Magma Ascent Dynamics

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.

Specific Heat Capacity Measurements of Selected Meteorites for Planetary Surface Temperature Modeling

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.

Discovery and Implications of Hidden Atomic-Scale Structure in a Metallic Meteorite

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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The M3 project: 3 – Global abundance distribution of hydrated silicates at Mars

1,2Lucie Riu,2,3John Carter,2François Poulet
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114809]
1Institut of Space and Astronautical Science (ISAS), Japanese Aerospace eXploration Agency (JAXA), Sagamihara, Japan
2Institut d’Astrophysique Spatiale (IAS), Université Paris-Saclay, Orsay, France
3Laboratoire d’Astrophysique de Marseille (LAM), Marseille, France
Copyright Elsevier

This paper is the third paper of a series that provides the modal mineralogy of the Martian surface (M3 project) at the global scale using near-infrared hyperspectral imagery. Numerous locations at the surface of Mars have previously been identified to harbor hydrated minerals which offer unique insights on the past water activity at the red planet. A radiative transfer model has been used to reproduce the spectra of these locations, based on the OMEGA instrument (Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité). Here we present the methodology applied to derive the hydrated quantitative composition and the first global compositional maps of hydrated minerals at Mars. Millions of spectra have been modelled to extract the modal composition of the hydrated locations, excluding sulfate-rich units. The lithology is summarized with 11 compositional maps of hydrated minerals at global scale at a sub-kilometer resolution. The hydrated mineralogy is dominated by an end-member of Fe-hydroxide, Fe- and Al-phyllosilicates and Fe/Mg micas which have on average an abundance >6 vol% and are spread globally on the identified regions. Locally, spots with high abundance (>20 vol%) of Al-smectite and Chlorite are also identified. The abundance of hydrated minerals is highest in Marwth Vallis, Nili Fossae and Meridiani Planum. However, the primary minerals almost always account for more than 50% of the composition. The modelling offers an opportunity to do local analysis of prospective landing sites and prepare for the upcoming landed missions. In the landing site for the ExoMars2022 and Mars2020 rovers, the obtained composition is in agreement with the expected detected mineralogy which demonstrates the robustness of the model and also offers a representation of the compositional variability. These global maps open the way to follow-up studies that will provide an in-depth characterization of the compositional gradients in local settings. Additionally, these compositional maps can 1) be used to calculate the water content namely potential amount of water stored within the quantified minerals and 2) provide information about the ISRU potential.

The Pecora Escarpment (PCA) 91020 EL3 chondrite and deformation on the EL3 asteroid

1,2Y. Boleaga,2,3,4M. K. Weisberg,4,5J. M. Friedrich,3,4D. S. Ebel
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13762]
1City College, City University of New York, New York, New York, 10031 USA
2Department of Physical Sciences, Kingsborough College CUNY, Brooklyn, New York, 11235 USA
3Department of Earth and Environmental Science, CUNY Graduate Center, New York, New York, 10016 USA
4Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, 10024 USA
5Department of Chemistry, Fordham University, Bronx, New York, 10458 USA
Published by arrangement with John Wiley & Sons

We present the results of our study of two thin sections of Pecora Escarpment (PCA) 91020, a heavily shocked EL3 chondrite, to characterize the sizes, shapes, orientations, and mineral compositions of its chondrules and opaque nodules. We also studied the mildly shocked Queen Alexandra Range (QUE) 94594 EL3 chondrite for comparison. PCA 91020 appears to show the evidence of deformation throughout the meteorite in both the chondrules and the opaque (metal–sulfide) nodules. Aspect ratios of the chondrules in PCA 91020 are greater than in the mildly shocked QUE 94594. Aspect ratios of the more ductile metal grains are higher than those of the chondrules in both sections of PCA 91020 and in QUE 94594. The data suggest that the chondrules and metal-rich nodules in PCA 91020 were elongated (flattened) to a greater degree and show a preferred orientation in comparison to objects in typical EL3 chondrites such as QUE 94594. The chondrule and metal-rich nodule deformation and foliation in PCA 91020 were likely produced by an impact on the EL3 asteroid. However, there are some inconsistencies in reconciling an impact hypothesis with all of the observations. Scenarios of hot accretion and/or overburden compaction during progressive (potentially rapid, hot) accretion to explain the deformation cannot be completely ruled out. Also, heavily shocked E3 chondrites, like PCA 91020, are relatively rare, suggesting the impacts that may have compacted chondrites, although potentially frequent, were of weak magnitude.

Oxygen and Aluminum-Magnesium Isotopic Systematics of Presolar Nanospinel Grains from CI Chondrite Orgueil

1Nan Liu,2Nicolas Dauphas,3,4Sergio Cristallo,4,5Sara Palmerini,4,5Maurizio Busso
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.11.022]
1Department of Physics, Washington University in St. Louis, MO 63130, USA
2Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, IL 60637, USA
3INAF, Osservatorio Astronomico d’Abruzzo, Via Mentore Maggini snc, 64100 Teramo, Italy
4INFN, Sezione di Perugia, Via A. Pascoli snc, 06123 Perugia, Italy
5Department of Physics and Geology, University of Perugia, Via A. Pascoli snc, I-06123 Perugia, Italy
Copyright Elsevier

Presolar oxide grains have been previously divided into several groups (Group 1 to 4) based on their isotopic compositions, which can be tied to several stellar sources. Much of available data was acquired on large grains, which may not be fully representative of the presolar grain population present in meteorites. We present here new O isotopic data for 74 small presolar oxide grains (∼200 nm in diameter on average) from Orgueil and Al-Mg isotopic systematics for 25 of the grains. Based on data-model comparisons, we show that (i) Group 1 and Group 2 grains more likely originated in low-mass first-ascent (red giant branch; RGB) and/or second-ascent (asymptotic giant branch; AGB) red giant stars and (ii) Group 1 grains with (26Al/27Al)0 ⪆ 5×10−3 and Group 2 grains with (26Al/27Al)0 ⪅ 1×10−2 all likely experienced extra circulation processes in their parent low-mass stars but under different conditions, resulting in proton-capture reactions occurring at enhanced temperatures. We do not find any large 25Mg excess in Group 1 oxide grains with large 17O enrichments, which provides evidence that 25Mg is not abundantly produced in low-mass stars. We also find that our samples contain a larger proportion of Group 4 grains than so far suggested in the literature for larger presolar oxide grains (≥ 400 nm). We also discuss our observations in the light of stellar dust production mechanisms.

Extraterrestrial dust as a source of bioavailable iron contributing to the ocean for driving primary productivity

1N. G. Rudraswami,1M. Pandey,2M. J. Genge,1D. Fernandes
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13764]
1CSIR-National Institute of Oceanography, Dona Paula, Goa, 403004 India
2Department of Earth Science and Engineering, Imperial College London, London, SW7 2AZ UK
Published by arrangement with John Wiley & Sons

Bioavailable Fe is an essential nutrient for phytoplankton that enables the organisms to flourish and draw down atmospheric CO2 thus affecting global climatic conditions. In marine locales, remote from the continents, extraterrestrial dust provides an important source of Fe and thus moderates primary productivity. Here, we provide constraints on partitioning of extraterrestrial Fe between seawater and sediments from the observations of dissolution and the alteration of cosmic spherules recovered from deep-sea sediments and Antarctica. Of the ∼3000–14,000 t a−1 extraterrestrial dust that reaches Earth’s surface, ∼2–5% material falling in the oceans survives in marine sediments while the remainder is liberated into seawater. Both processes contribute ∼(3–10) × 10−8 mol Fe m−2 yr−1. The Fe contribution of surviving particles due to etching is estimated to be ∼10% of Fe contribution of meteoric smoke. Changes in extraterrestrial dust flux over geological time scales not only vary Fe delivery to the oceans by up to three orders of magnitude but also the partitioning of Fe between surface and abyssal waters depending on entry velocity and evaporation.

Multiple shock events recorded in the Northwest Africa 2139 LL6 chondrite: Implications for collisional histories of the LL chondrite parent body

1,2Atsushi Takenouchi,3Hirochika Sumino,4Karin Shimodate,2Akira Yamaguchi
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13768]
1The Kyoto University Museum, Kyoto University, Yoshida-honmachi, Sakyo, Kyoto, 606-8501 Japan
2National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo, 190-8518 Japan
3General Systems Studies, Graduate School of Arts and Science, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo, 153-8902 Japan
4Department of Physics, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8654 Japan
Published by arrangement with John Wiley & Sons

LL chondrites have experienced multiple shock events; however, the relations of each shock event and their timing have rarely been investigated. To demonstrate the relations between each shock texture and shock chronological ages, we conducted both petrological and chronological (40Ar/39Ar and I-Xe ages) studies using aliquots subsampled from the same chip of the Northwest Africa (NWA) 2139 LL6 chondrite. Our 40Ar/39Ar studies and petrological observation reveal that NWA 2139 recorded at least three impact events before 4.17 ± 0.10 Ga, thus resulting in a complex brecciated texture, silicate darkening, and thick shock veins. An intense heating event occurred at 4.17 ± 0.10 Ga, which recrystallized the thick veins and healing cracks. Then, a weak shock event occurred at <3.9 Ga. Combined with 40Ar/39Ar data of other LL chondritic materials, this study supports that the LL chondrite parent body was possibly broken up by 1.7 Ga, and that most of the breakup likely occurred within 3.8–4.2 Ga.