¹Noriyuki Kawasaki,¹Sohei Wada,² Changkun Park,³Naoya Sakamoto,^1,3,4Hisayoshi Yurimoto
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.03.045]
¹Department of Natural History Sciences, Hokkaido University, Sapporo 060-0810, Japan
²Division of Earth-System Sciences, Korea Polar Research Institute, Incheon 21990, Republic of Korea
³Isotope Imaging Laboratory, Creative Research Institution, Hokkaido University, Sapporo 001-0021, Japan
⁴Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara 252-5210, Japan
Copyright Elsevier

Fine-grained Ca-Al-rich inclusions (FGIs) in CV chondrites are suggested to be condensates formed directly from the solar nebular gas. Al−Mg mineral isochrons of seven FGIs from reduced CV chondrites Efremovka, Vigarano, Thiel Mountains 07007, and Northwest Africa 8613 were obtained via in situ Al–Mg isotope measurements using secondary ion mass spectrometry. The slopes of the mineral isochrons for seven FGIs exhibit statistically significant variations in initial ²⁶Al/²⁷Al ratios, (²⁶Al/²⁷Al)₀, ranging from (5.19 ± 0.17) to (3.35 ± 0.21) × 10⁻⁵, which correspond to a relative age spread of 0.44 ± 0.07 Myr. Inferred upper limit of (²⁶Al/²⁷Al)₀for the FGIs is identical to the Solar System (²⁶Al/²⁷Al)₀ of ∼5.2 × 10⁻⁵ as determined by whole-rock Al–Mg isochron studies for CAIs in CV chondrites. The intercepts of the mineral isochrons, the initial ²⁶Mg/²⁴Mg ratios the FGIs formed with, are consistent with Mg-isotope evolution path of a solar-composition nebular gas. The observed variations in (²⁶Al/²⁷Al)₀ for FGIs are essentially similar to those (∼5.2 to ∼4.2 × 10⁻⁵) for coarse-grained, igneous CAIs of CV chondrites that are formed by melting and solidification. If ²⁶Al was distributed homogeneously in the forming region, then our data indicate that thermal processes of condensation and melting for CAI formation occurred contemporaneously and continued for at least ∼0.4 Myr at the very beginning of the Solar System. Alternatively, the observed variations in (²⁶Al/²⁷Al)₀ also indicate the possibility of heterogeneous distributions of ²⁶Al in the forming region, corresponding to a range of over at least 3.4 × 10^–5 < (²⁶Al/²⁷Al)₀ < 5.2 × 10^–5.

^1,2Julia Semprich,¹Justin Filiberto,¹Allan H.Treiman
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113779]
¹Lunar and Planetary Institute, USRA, 3600 Bay Area Bld., Houston, TX 77058, USA
²Astrobiology OU, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
Copyright Elsevier

Rock alteration processes on Venus are still poorly understood due to the limited geochemical data on surface rocks and uncertainties in atmospheric compositions. We use phase equilibria calculations to constrain mineral stabilities at Venus surface conditions for different rock and gas compositions resulting in the chemical system SiO₂-TiO₂-Al₂O₃-FeO-MgO-CaO-Na₂O-K₂O with C-O-H-S gas at varying O₂ and S₂fugacities. While the low concentrations of H₂O in the present-day atmosphere result in conditions, under which anhydrous mineral assemblages dominate, higher amounts of water, possibly during an earlier stage in Venus’ history, could have resulted in the formation of amphibole and biotite. Even in a sulfur-free atmosphere, carbonates would be stable only in alkali-rich basalts. The presence of SO₂ in the atmosphere, however, causes the formation of anhydrite. The stabilities of iron oxides and sulfides are highly sensitive to gas fugacities (i.e., the composition of the atmosphere), as well as temperature. While the modeled magnetite-hematite transition is located close to conditions relevant for planetary radius, the assemblage of anhydrite + hematite ± pyrite may be stable at higher elevations if a similar range of fO₂ as at the lowlands is assumed. Therefore, our model agrees with pyrite as the proposed cause of the high radar backscatter observed at high elevations in the northern highlands.

^1,2B. D. Byron,^1,2K. D. Retherford,²T. K. Greathouse,²D. Wyrick,³J. T. S. Cahill,⁴A. R. Hendrix,^1,2U. Raut,³K. E. Mandt,³B. W. Denevi
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2019JE006269]
¹Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX, USA
²Space Science and Engineering Department, Southwest Research Institute, San Antonio, TX, USA
³The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
⁴Planetary Science Institute, Tucson, AZ, USA
Published by arrangement with John Wiley & Son

Using data from the Lunar Reconnaissance Orbiter (LRO) Lyman Alpha Mapping Project (LAMP), we investigate the spectral properties of rayed craters in the far‐ultraviolet (FUV). Because LAMP is sensitive to the uppermost layer of the lunar surface and regolith grains, it is ideal for characterizing regolith maturity and space weathering products such as submicroscopic iron. We find that crater rays from a survey of the largest Copernican‐age craters have high Off‐band (155–190 nm)/On‐band (130–155 nm) albedo (Off/On) LAMP product ratios, consistent with immature regolith and low amounts of submicroscopic iron. The Off/On ratio of the highlands crater rays decreases linearly over time (0.095 per 100 My), and we use this trend to estimate the age of Jackson crater (~152 My). Some large young highlands craters (e.g., Tycho, Jackson, Giordano Bruno, and Necho) display lower ratio halos around the crater cavity, at regions where previous studies have suggested abundant impact melt exists. The lower Off/On ratio is likely due to the increased glass component of the regolith at these highlands regions, which would act to increase absorption at Off‐band wavelengths. We also find that ejecta blankets from large maria craters (e.g., Copernicus and Aristillus) have a similar Off/On ratio to the mature background highlands. This supports previous findings that determined that the rays from these craters are composed of highlands material excavated from beneath the maria and subsequently weathered to maturity.

¹A. J. Brown,²C. E. Viviano,³T. A. Goudge
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2019JE006011]
¹Plancius Research, Severna Park, MD, USA
²Johns Hopkins Applied Physics Laboratory, Laurel, MD, USA
³Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX, USAPublished by arrangement with John Wiley & Sons

A well‐preserved, ancient delta deposit, in combination with ample exposures of carbonate outcrops, makes Jezero Crater in Nili Fossae a compelling astrobiological site. We use Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) observations to characterize the surface mineralogy of the crater and surrounding watershed. Previous studies have documented the occurrence of olivine and carbonates in the Nili Fossae region. We focus on correlations between these two well‐studied lithologies in the Jezero crater watershed. We map the position and shape of the olivine 1 μm absorption band and find that carbonates are found in association with olivine which displays a 1 μm band shifted to long wavelengths. We then use Thermal Emission Imaging Spectrometer (THEMIS) coverage of Nili Fossae and perform tests to investigate whether the long wavelength shifted (redshifted) olivine signature is correlated with high thermal inertia outcrops. We find that there is no consistent correlation between thermal inertia and the unique olivine signature. We discuss a range of formation scenarios for the olivine and carbonate associations, including the possibility that these lithologies are products of serpentinization reactions on early Mars. These lithologies provide an opportunity for deepening our understanding of early Mars and, given their antiquity, may provide a framework to study the timing of valley networks and the thermal history of the Martian crust and interior from the early Noachian to today.

¹Dougal J. Ritson,^2,3Stephen J. Mojzsis,¹John. D. Sutherland
Nature Geoscience (in Press) Link to Article [DOI https://doi.org/10.1038/s41561-020-0556-7]
¹MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Cambridge, UK
²Department of Geological Sciences, University of Colorado, Boulder, CO, USA
Stephen J. Mojzsis
³Institute for Geological and Geochemical Research, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Budapest, Hungary
Stephen J. Mojzsis

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¹Erick J. Cano,¹Zachary D. Sharp,²Charles K. Shearer
Nature Geoscience (in Press) Link to Article [DOI https://doi.org/10.1038/s41561-020-0550-0]
¹Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM, USA
²Institute of Meteoritics, University of New Mexico, Albuquerque, NM, USA

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¹Shima Pilehvar,²Marlies Arnhof,³Ramón Pamies,⁴Luca Valentini,¹Anna-Lena Kjøniksen
Journal of Cleaner Production 247, 119177 Link to Article [https://doi.org/10.1016/j.jclepro.2019.119177]
¹Faculty of Engineering, Østfold University College, P.O. Box 700, 1757, Halden, Norway
²Advanced Concepts Team, ESA European Space Research and Technology Centre, Keplerlaan 1, TEC-SF, 2201AZ, Noordwijk, Netherlands
³Department of Materials Engineering and Manufacturing, Technical University of Cartagena, Cartagena, Murcia, Spain
⁴Department of Geosciences, University of Padua, 35131, Padua, Italy

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¹Ingo Leya et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13466]
¹Physics Institute, University of Bern, Sidlerstrasse 5, CH‐3012 Bern, Switzerland
Published by arrangement with John Wiley & Sons

We measured specific activities of the long‐lived cosmogenic radionuclides 60Fe in 28 iron meteorites and 53Mn in 41 iron meteorites. Accelerator mass spectrometry was applied at the 14 MV Heavy Ion Accelerator Facility at ANU Canberra for all samples except for two which were measured at the Maier‐Leibnitz Laboratory, Munich. For the large iron meteorite Twannberg (IIG), we measured six samples for 53Mn. This work doubles the number of existing individual 60Fe data and quadruples the number of iron meteorites studied for 60Fe. We also significantly extended the entire 53Mn database for iron meteorites. The 53Mn data for the iron meteorite Twannberg vary by more than a factor of 30, indicating a significant shielding dependency. In addition, we performed new model calculations for the production of 60Fe and 53Mn in iron meteorites. While the new model is based on the same particle spectra as the earlier model, we no longer use experimental cross sections but instead use cross sections that were calculated using the latest version of the nuclear model code INCL. The new model predictions differ substantially from results obtained with the previous model. Predictions for the 60Fe activity concentrations are about a factor of 2 higher, for 53Mn, they are ~30% lower, compared to the earlier model, which gives now a better agreement with the experimental data.

¹R.D.Hanna,²V.E.Hamilton,³C.W.Haberle,^4,5A.J.King,⁶N.M.Abreu,^7,8J.M.Friedrich
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113760]
¹Jackson School of Geosciences, University of Texas at Austin, Austin, TX 78712, USA
²Department of Space Studies, Southwest Research Institute, Boulder, CO 80302, USA
³School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA
⁴School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
⁵Planetary Materials Group, Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK
⁶Earth Science Program, Pennsylvania State University, Du Bois, PA 15801, USA
⁷Department of Chemistry, Fordham University, Bronx, NY 10458, USA
⁸Department of Earth and Planetary Sciences, American Museum of Natural History, New York, NY 10024, USA
Copyright Elsevier

Using infrared (IR) spectroscopy of thin sections, we characterize the relative degree of aqueous alteration and subsequent heating of a suite of CM chondrites to document spectral indicators of these processes that can contextualize observations of carbonaceous asteroids. We find that the progressive aqueous alteration of CMs manifests in two spectral regions. The low-wavenumber region (1200–400 cm⁻¹; 8–25 μm) records the increasing proportion of MgFe phyllosilicates relative to anhydrous silicates as aqueous alteration proceeds, with a highly correlated shift of the Christiansen feature (CF) to lower wavenumber and the SiO bending band minimum to higher wavenumber, and an increase in depth of the Mg-OH band (~625 cm⁻¹). The strongest correlation (R² = 0.90) with petrologic subtype is the distance between the CF and SiO stretching band minimum, which predicts the petrologic subtype of the sample to within 0.1. The high-wavenumber region (4000–2500 cm⁻¹, ≤3.33 μm) probes the variation in abundance and composition of MgFe serpentine and tochilinite among the altered CMs. All moderately to highly altered CMs (≤2.3) have an OH/H₂O (‘3 μm’) band emission maximum of 3690 cm⁻¹ (2.71 μm) indicative of Mg-bearing serpentine, and mildly aqueously altered CMs (≥ 2.5) have a wider band with a complex shape that results from contributions of Fe-bearing serpentine and tochilinite. Among weakly heated CMs (Stage II; 300–500 °C), the low-wavenumber region exhibits spectral features resulting from the dehydration and dehydroxylation of phyllosilicates that include broadening of the SiO stretching band and a shift of its minimum to lower wavenumber, and the disappearance of the Mg-OH band. The location of the SiO bending band minimum appears to be unaffected by mild heating. Extensively heated CMs (Stage III+; >500 °C) have a low-wavenumber region dominated by the spectral features of secondary, Fe-bearing olivine and low-Ca pyroxene and thus are readily distinguished from unheated and mildly heated CMs. The OH/H₂O band of all heated CMs is broad and rounded with an emission peak at higher wavenumbers (≤3636 cm⁻¹; ≥2.75 μm) than in unheated CMs. However, spectral and petrographic evidence suggests that our heated CMs have been compromised by terrestrial rehydration. Our study confirms that thermal metamorphism effects are concentrated within the matrix and suggests that the matrix of the CM WIS 91600 had a CI-like mineralogy prior to heating.

¹Jaques S. Schmidt,²Ruth Hinrichs
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13467]
¹Division of Geochemistry, PETROBRAS R&D Center, Rua Horácio Macedo 950, Rio de Janeiro, RJ, Brazil
²Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves 9500, Porto Alegre, RS, Brazil
Published by arrangement with John Wiley & Sons

A Raman method to estimate the aromatization degree of carbonaceous matter (CM) was established, and calibrated by literature data respecting differences in acquisition procedures. The generated equations allowed a comparison of the G‐band width to vitrinite reflectance, and to additional structural organization parameter extracted from X‐ray powder diffraction. The relations between aromatization degree and peak temperatures from literature were then propagated to G‐band width parameter. The applicability of these geothermometers is demonstrated by the consistency of data obtained for carbonaceous chondrites with previous estimations. Since the CM aromatization is controlled by peak temperature and time span, it is possible to estimate the duration of chondrite’s heating events. The G‐band width relation to elemental ratio trends of organic matter in chondrites, interplanetary dust particles, glucose, and saccharose‐based semi‐coke favors synthesis by formose route. These findings provide new approaches for the future development of chemical kinetic models for organic matter of chondrites. A reliable chemical model may allow the external calibration of numerical models for accurately evaluating the peak temperatures and cooling durations of chondrites.