¹Saverio Cambioni,²Katherine de Kleer,³Michael Shepard
Journal of Geophysical Research (Planets) (in Press) Open Access Link to Article [https://doi.org/10.1029/2021JE007091]
¹Department of Earth, Atmospheric & Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
²Division of Geological & Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
³Department of Environmental, Geographical & Geological Sciences, Bloomsburg University, Bloomsburg, PA, USA
Published by arrangement with John Wiley & Sons

Main-belt asteroid (16) Psyche is the largest M-type asteroid, a class of object classically thought to be the metal cores of differentiated planetesimals and the parent bodies of the iron meteorites. de Kleer, Cambioni, and Shepard (2021) presented new data from the Atacama Large Millimiter Array (ALMA), from which they derived a global best-fit thermal inertia and dielectric constant for Psyche, proxies for regolith particle size, porosity, and/or metal content, and observed thermal anomalies that could not be explained by surface albedo variations only. Motivated by this, here we fit a model to the same ALMA dataset that allows dielectric constant and thermal inertia to vary across the surface. We find that Psyche has a heterogeneous surface in both dielectric constant and thermal inertia but, intriguingly, we do not observe a direct correlation between these two properties over the surface. We explain the heterogeneity in dielectric constant as being due to variations in the relative abundance of metal and silicates. Furthermore, we observe that the lowlands of a large depression in Psyche’s shape have distinctly lower thermal inertia than the surrounding highlands. We propose that the latter could be explained by a thin mantle of fine regolith, fractured bedrock, and/or implanted silicate-rich materials covering an otherwise metal-rich surface. All these scenarios are indicative of a collisionally evolved world.

¹Aditi Pandey,²Monique Nguyen-Vu,¹Paul Schwab
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115096]
¹Department of Soil and Crop Sciences, Texas A&M University, College Station, TX 77843, United States of America
²Department of Biology, Texas A&M University, College Station, TX 77843, United States of America
Copyright Elsevier

Spectral data from satellite and rover missions on Mars identified significant abundances of amorphous phases in most samples analyzed, and SiO2 is the principal amorphous constituent in the Gale crater. Identifying and quantifying these short-range ordered, highly reactive phases is challenging but necessary to gain insight into the evolution of these materials. Terrestrial analogs are frequently employed to allow detailed analyses that cannot be performed on Martian samples. Historically, chemical extraction techniques have been extensively used to characterize amorphous materials in terrestrial soils, but most automated systems are complex, expensive, and limited to analyzing a single sample at one time. This study aims to develop a cost-effective apparatus that will allow latitude in choosing an extractant, process several samples simultaneously, enable rapid sampling over time without interruption and provide the resolution for quantitative differentiation of rapidly dissolving SiO2(a) phases in natural samples. Dissolution rates as a function of time were used as input for kinetic models to estimate the abundances of amorphous phases. When 2 M Na2CO3 is used as the extractant, dissolution rates differ significantly between secondary phases such as opal and primary glass phases. A stronger base, NaOH, is necessary for the complete dissolution of basaltic glass. Palagonitic tuffs from Iceland (proposed analogs of Martian soils) with >90% (w/w) amorphous composition were analyzed with 2 M Na2CO3 in the proposed apparatus, and both primary glass and secondary SiO2 appear to be present. Using the kinetic model of the dissolution, the palagonitic tuff has a composition of approximately 25% (w/w) of a rapidly reacting amorphous phase and 13% (w/w) of the slower reacting glass-like phase. The proposed high-efficiency analytical method can be applied to screen through multiple terrestrial analogs and archive dissolution kinetics of many standard amorphous minerals. Although this paper focuses on extracting SiO2 (a), the same setup can be applied to study time-based dissolution reactions using other extractants such as ammonium oxalate oxalic acid.

¹Yevgen Grynko,²Yuriy Shkuratov,¹Samer Alhaddad,¹Jens Förstner
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115099]
¹Department of Theoretical Electrical Engineering, Paderborn University, Warburger Str. 100, 33102 Paderborn, Germany
¹Institute of Astronomy of Kharkiv National University, Sumska Str. 35, 61022 Kharkiv, Ukraine
Copyright Elsevier

We model negative polarization, which is observed for planetary regoliths at backscattering, solving a full wave problem of light scattering with a numerically exact Discontinuous Galerkin Time Domain (DGTD) method. Pieces of layers with the bulk packing density of particles close to 0.5 are used. The model particles are highly absorbing and have irregular shapes and sizes larger than the wavelength of light. This represents a realistic analog of low-albedo planetary regoliths. Our simulations confirm coherent backscattering mechanism of the origin of negative polarization. We show that angular profiles of polarization are stabilized if the number of particles in a layer piece becomes larger than ten. This allows application of our approach to the negative polarization modeling for planetary regoliths.

¹Ekaterian Magg et al. (>10)
Astronomy & Astrophysics 661, A140 Open Access Link to Article [DOI https://doi.org/10.1051/0004-6361/202142971]
¹Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany

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

¹S.Griffin et al. (>10)
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2021JE007080]
¹School of Geographical and Earth Sciences, University of Glasgow, Glasgow, UK
Published by arrangement with John Wiley & Sons

The Martian nakhlite meteorites, which represent multiple events that belong to a single magma source region represent a key opportunity to study the evolution of Martian petrogenesis. Here 16 of the 26 identified nakhlite specimens are studied using coupled electron backscatter diffraction (EBSD) and emplacement end-member calculations. EBSD was used to determine shape preferred orientation (SPO) of contained augite (high Ca-clinopyroxene) phenocrysts by considering their crystallographic preferred orientation (CPO). Parameters derived from EBSD, and energy dispersive X-ray spectroscopy (EDS) data were used in basic emplacement models to assess their dominant mechanism against three end-member scenarios: thermal diffusion, crystal settling, and crystal convection. Results from CPO analyses indicate low intensity weak-moderate CPO. In all samples, a consistent foliation within the <001> axes of augite are observed typically coupled with a weaker lineation CPO in one of the other crystallographic axes. These CPO results agree best with crystal settling being the dominant emplacement mechanism for the nakhlites. Modelled crystal settling results identify two distinguishable groups outside of the model’s resolution indicating the presence of secondary emplacement mechanisms. Comparison of the two identified groups against petrofabric, geochemical, and age parameters indicate random variability between individual meteorites. Therefore, coupled petrofabric and emplacement modelling results identify an overarching characteristic of a dominant crystal settling emplacement mechanism for the nakhlite source volcano despite exhibiting random variation with each discharge through time.

¹G.M.Wong et al. (>10)
Journal of Geophysical Research (Planets)(In Press) Open Access Link to Article [https://doi.org/10.1029/2021JE007084]
¹Department of Geosciences, The Pennsylvania State University, University Park, PA, USA
Published by arrangement with John Wiley & Sons

The Mars Science Laboratory (MSL) Curiosity rover has been assessing the habitability and geologic history of Gale crater, Mars since landing in 2012. One of the primary objectives of the mission was to investigate a clay-bearing unit identified using orbital spectral data, designated the Glen Torridon (GT) region. This region was of particular interest because of its elevated abundance of clay minerals that may have preserved geochemical evidence of ancient habitable environments. The Curiosity rover explored the GT region for ∼750 sols and analyzed eight drilled samples with the Sample Analysis at Mars (SAM) instrument suite using evolved gas analysis-mass spectrometry. Evolved sulfur-bearing gases provided insight about the composition of sulfur-containing compounds in Martian samples. Evolved gases were analyzed by three methods to understand the oxidation state of sulfur in the samples: (1) SO₂ evolution temperature, (2) quadratic discriminant analysis comparing SAM data to SAM-like laboratory investigations, and (3) sulfur isotope values from evolved ³⁴SO₂/³²SO₂. The results of these three methods were consistent with the majority of sulfur in the GT region being in an oxidized state, but two of the eight samples analyzed by SAM were consistent with the presence of small amounts of reduced sulfur. The oxidized and reduced sulfur could have a variety of sources and represents a nonequilibrium assemblage that could have supported putative ancient chemolithotrophic metabolisms.

^1,2Thomas Smith,¹Ingo Leya
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13827]
¹Physics Institute, University of Bern, Sidlerstrasse 5, Bern, CH-3012 Switzerland
²State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, 19 Beitucheng Western Road, Chaoyang District, Box 9825, Beijing, 100029 China
Published by arrangement with John Wiley & Sons

The live 129I-129Xe dating technique, which internally corrects for shielding, is particularly well suited for large iron meteorites, for which shielding corrections might be difficult to obtain. In addition, the half-life of 129I of 16 Ma would allow the study of the important question of the constancy—or variability—of the galactic cosmic rays over a time scale not covered by other cosmogenic nuclides. Here, we present the results of a noble gas study of metal samples and adjacent troilite inclusions from the four IIIAB iron meteorites Cape York (including Agpalilik), Casas Grandes, Trenton, and Grant. The major result is that we can directly determine 129Xenc concentrations caused by (live) 129I decay for Cape York, Casas Grandes, Trenton, and Grant. The 129Xenc concentrations can be used, if combined to 129I activity concentrations (not measured by us), to calculate cosmic ray exposure (CRE) ages using the (live) 129I-129Xe chronometer. For the light noble gases measured in metal and troilite samples, the new data confirm the earlier estimates of a production rate ratio 21Necos(troilite)/21Necos(metal) in the range 3.08–3.53. Surprisingly, 38Arcos in troilite from Agpalilik and Casas Grandes is only, respectively, ~36% and ~44% relative to that in the respective metal phases. Considering that 38Arcos is only produced from iron but not from sulfur, the 38Arcos concentration measured in troilite is expected to be ~64% relative to that in adjacent metal, that is, some 38Arcos is missing. Considering krypton in troilite, only 80Kr, 82Kr, and 83Kr are higher than the blank, likely indicating a spallogenic contribution. On average, ~4.2% of measured 80Kr, ~2.5% of 82Kr, and ~11.6% of 83Kr are spallogenic.

¹Max W. Schmidt,¹Giuliano Kraettli
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2022JE007187]
¹ETH, Zuerich, Switzerland
Published by arrangement with John Wiley & Sons

Eleven isobaric experimental series simulate the fractional crystallization of a 1150 km deep lunar magma ocean. Crystallization begins at 1850 ^oC with olivine (to 32 per cent solidified, pcs), followed at 1600 ^oC by olivine+opx±Cr-spinel (to 62 pcs), at 1210 ^oC cpx+plagioclase±olivine±Ti-spinel (to 97 pcs) and at 1060 ^oC quartz+cpx+plagioclase+Ti-spinel, leaving 1.8 wt% residual magma that crystallizes minor K-feldspar and apatite in addition. Melt compositions remain near 45 wt% SiO₂, while FeO increases from 11 to 26 wt%, TiO₂ peaks at 4 wt% at Ti-spinel saturation.

The available experimental liquid lines of descent yields an overall fractional crystallization sequence of olivine→opx→cpx+plagioclase→quartz→FeTi-oxide. Plagioclase appears concomitantly with cpx, a result of the low magma ocean floor pressures (≤ 1 GPa) after 66-76 % of olivine+opx-fractionation. A few wt% of FeTi-oxides form mostly once the quartz+plagioclase+cpx-cotectic is reached, cumulates densities remain ≤3740 kg/m³. Scaled to a full magma ocean, plagioclase appears at 210-120 km depth, mainly as a function of bulk Al₂O₃. As buoyancy driven plagioclase-cpx separation is likely limited, these depths may correspond to the primordial lunar crustal thickness. Allowing for complete plagioclase flotation to the quartz+plagioclase+cpx+FeTi-oxide±olivine cotectic yields 95-70 km primordial crust of anorthosite and quartz-gabbro, far in excess of the 35-50 km observed. This supports an overturn of primordial layers, re-melting of dense gabbroic cumulates in the harzburgitic cumulate mantle leading to further mixing and differentiation. We posit that such complex density induced convection led to a lunar marble cake mantle with primitive and fairly evolved reprocessed cumulates next to each other.

¹R.J.Smith et al. (>10)
Journal of Geopyhsical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2021JE007128]
¹Department of Geosciences, SUNY Stony Brook, Stony Brook, NY, 11794 USA
Published by arrangement with John Wiley & Sons

The Curiosity rover in Gale crater is investigating a mineral transition observed from orbit – an older “clay unit” to a younger “sulfate unit” – hypothesized to reflect the aridification of Mars’ climate. Below this transition, the rover detected crystalline Ca-sulfates with minor Fe-sulfates but also found that some fraction of a rock’s bulk SO3 is often in the poorly constrained X-ray amorphous component. Here, we characterize the abundances and compositions of the X-ray amorphous sulfur-bearing phases in 19 drilled samples using a mass balance approach, and in a subset of 5 samples using evolved SO2 gas measured by the SAM instrument. We find that ∼20-90 wt% of a sample’s bulk SO3 is in the X-ray amorphous state and that X-ray amorphous sulfur-bearing phase compositions are consistent with mixtures of Mg-S, Fe-S, and possibly Ca-S phases, likely sulfates or sulfites. These phases reside in the bedrock, perhaps as cementing agents deposited with detrital sediments or during early diagenesis, and in diagenetic alteration halos deposited after lithification during late diagenesis. The likely presence of highly soluble Mg-sulfates in the rocks suggests negligible fluid flow through the bedrock post-Mg-sulfate deposition. The X-ray amorphous sulfur-bearing phases probably became amorphous through dehydration in the current Martian atmosphere or inside the CheMin instrument. X-ray amorphous sulfur-bearing materials likely contribute to orbital spectral detections of sulfates, and so our results help form multiple hypotheses to be tested in the sulfate unit and are important for understanding the evolution of the Martian surface environment at Gale crater.

¹E.Rader,¹S.Ackiss,²A.Sehlke,³J.Bishop,⁴B.Orrill,¹K.Odegaard,¹M.Meier,^1,5A.Doloughan
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115084]
¹University of Idaho, Department of Geological Sciences, Moscow, ID 83844, USA
²NASA Ames Research Center/ Bay Area Environmental Research Institute, Moffett Field, CA 94035, USA
³SETI Institute, Moutain View, CA, USA
⁴Arizona State University, Tempe, AZ, USA
⁵Terracon, Olathe, KS, USA
Copyright Elsevier

The microcrystalline texture in basaltic lava, scoria, and spatter can vary widely from pure glass to holocrystalline due to complex cooling histories after eruption. How quickly a molten rock cools is a function of the environmental surroundings, including water, ice, sustained heat source, and atmospheric conditions. Thus, petrologic texture serves as an indicator of cooling history captured in the rock record. As basalt is a common component of terrestrial bodies across the solar system, relating the abundance of crystalline components to spectral character would allow for a more thorough understanding of the cooling history and emplacement conditions on planetary surfaces. Visible/near-infrared (VNIR) reflectance spectroscopy has been used to examine the absorptions associated with volcanic glass, however, the non-linearity of absorption features in this spectral region requires complex spectral unmixing modeling to achieve modal percentages of minerals. Here we present evidence that average reflectance from 500 to 1000 nm (referred to as R_500–1000) of solid surface samples is indicative of the crystal texture and degree of glassiness of basaltic rocks. Several factors, such as sample surface roughness, lichen cover, coatings, weathering, and chemical composition can affect the R_500–1000 of a sample. However, our data indicate that these factors can be sufficiently controlled during sample selection to attribute relative glassiness values to basaltic surfaces. This quick and straightforward method requires no sample preparation or modeling and is demonstrated with training data from sixteen rocks from five basaltic flow fields with differing mineralogy, surface qualities, and geochemistry across Idaho and Oregon, USA. We further test our relationship with two published datasets of synthetic and natural basalts, as well as a subset of our own data collected with our methods to examine the sensitivities of the correlation. This method has the potential to broadly identify glassier basaltic lavas across planetary surfaces. This could be applied toward understanding lava eruption temperatures, cooling rates, magma petrogenesis, paleoclimate reconstruction, and astrobiology due to the involvement of water in quenching of lava.