Hyperspectral polarimetry of eight Apollo soils

1Lingzhi Sun,1Paul Lucey,2Casey I.Honniball,1Macey Sandford,1Emily S.Costello,1Liliane Burkhard,3Reilly Brennan,1Chiara Ferrari-Wong
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114740]
1Hawai‘i Institute of Geophysics and Planetology, Department of Earth Sciences, University of Hawai‘i at Mānoa, Honolulu, HI 96822, USA
2NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
3Georgia Institute of Technology, Atlanta, GA 30332, USA
Copyright Elsevier

The reflected light from the lunar surface is polarized and contains perpendicular () and parallel () branches. To provide supporting data for the first polarimetric camera (PolCam) on board the Korean Pathfinder lunar orbiter, in this work, we built a polarimeter and measured the polarized spectra for eight Apollo soils that span a wide range in composition and maturity. We found a linear correlation between reflectance R and the difference of perpendicular and parallel branches: , and b’ might be sensitive to the grain size of lunar soils. The regression coefficient b’ can be derived from both positive and negative polarization spectra and has little dependence on wavelength, thus it has great potential in estimating grain size for lunar soils. We also used radiative transfer equations to calculate the real index of optical constants and to reproduce the perpendicular and parallel polarized spectra for the lunar soils. We correlated polarimetry indexes including polarization degree () and the difference of the perpendicular and parallel branches () with the abundances of FeO and TiO2 and soil maturity, and our result indicates that these two polarimetry indexes show dependence on both the compositions and soil maturity.

A compositional link between rocky exoplanets and their host stars

1,2Vardan Adibekyan et al. (>10)
Science 374, 330-332 Link to Article [DOI: 10.1126/science.abg8794]
1Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, Centro de Astrofísica da Universidade do Porto, 4150-762 Porto, Portugal.
2Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, 4169-007 Porto, Portugal.
Reprinted with permission from AAAS

Stars and planets both form by accreting material from a surrounding disk. Because they grow from the same material, theory predicts that there should be a relationship between their compositions. In this study, we search for a compositional link between rocky exoplanets and their host stars. We estimate the iron-mass fraction of rocky exoplanets from their masses and radii and compare it with the compositions of their host stars, which we assume reflect the compositions of the protoplanetary disks. We find a correlation (but not a 1:1 relationship) between these two quantities, with a slope of >4, which we interpret as being attributable to planet formation processes. Super-Earths and super-Mercuries appear to be distinct populations with differing compositions, implying differences in their formation processes.

Characteristics, origins, and biosignature preservation potential of carbonate-bearing rocks within and outside of Jezero crater

1J.D.Tarnas et al. (>10)
Journal of Geophysical Research (Planets) (In Press) Link to Article [https://doi.org/10.1029/2021JE006898]
1NASA Jet Propulsion Laboratory, California Institute of Technology
Publishe by Arrangement with John Wiley & Sons

Carbonate minerals have been detected in Jezero crater, an ancient lake basin that is the landing site of the Mars 2020 Perseverance rover, and within the regional olivine-bearing (ROB) unit in the Nili Fossae region surrounding this crater. It has been suggested that some carbonates in the margin fractured unit, a rock unit within Jezero crater, formed in a fluviolacustrine environment, which would be conducive to preservation of biosignatures from paleolake-inhabiting lifeforms. Here we show that carbonate-bearing rocks within and outside of Jezero crater have the same range of visible-to-near-infrared carbonate absorption strengths, carbonate absorption band positions, thermal inertias, and morphologies. Thicknesses of exposed carbonate-bearing rock cross-sections in Jezero crater are ∼75-90 meters thicker than typical ROB unit cross-sections in the Nili Fossae region, but have similar thicknesses as ROB unit exposures in Libya Montes. These similarities in carbonate properties inside and outside of Jezero crater is consistent with a shared origin for all of the carbonates in the Nili Fossae region. Carbonate absorption minima positions indicate that both Mg- and more Fe-rich carbonates are present in the Nili Fossae region, consistent with the expected products of olivine carbonation. These estimated carbonate chemistries are similar to those in martian meteorites and the Comanche carbonates investigated by the Spirit rover in Columbia Hills. Our results indicate that hydrothermal alteration is the most likely formation mechanism for non-deltaic carbonates within and outside of Jezero crater.

Orientations of planar cataclasite zones in the Chicxulub peak ring as a ground truth for peak ring formation models

1Naoma McCall,1,2Sean P.S.Gulick,3Brendon Hall,4.5Auriol S.P.Rae,4Michael H.Poelchau,6Ulrich Riller,7Johanna Lofi,8Joanna V.Morgan
Earth and Planetary Science Letters 576, 117236 Link to Article [https://doi.org/10.1016/j.epsl.2021.117236]
1University of Texas at Austin, Jackson School of Geosciences, Institute for Geophysics & Department of Geological Sciences, J.J. Pickle Research Campus, Austin, TX 78758, USA
2Center for Planetary Systems Habitability, University of Texas at Austin, Austin, TX, USA
3Enthought, Inc., Austin, TX, USA
4Institute of Earth and Environmental Sciences—Geology, Albert-Ludwigs Universität Freiburg, Albertstrasse 23b, Freiburg 79110, Germany
5Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
6Institut für Geologie, Universität Hamburg, Bundesstrasse 55, Hamburg, 20146, Germany
7Géosciences Montpellier, Université de Montpellier, CNRS, France
8Department of Earth Science and Engineering, Imperial College London, SW7 2AZ, UK
Copyright Elsevier

Hypervelocity impact cratering is an important geologic process but the rarity of large terrestrial impact craters on Earth and the limited technical options to study cratering processes in the laboratory hinders our understanding of large-scale impact processes. Drill core recovered from the peak ring of the Chicxulub impact crater during International Ocean Discovery Program (IODP)/International Continental scientific Drilling Program (ICDP) Expedition 364 provides an opportunity to examine target rock deformation and thus, to assess cratering models in this regard. Using oriented computer tomography (CT) scans and line scan images of the core, we present the orientations of mm-to-cm-scale planar cataclasite and ultracataclasite zones in the deformed granitoid target rock of the peak ring. In the upper 470 m of the target rock, the cataclasite zones dip towards the crater center, whereas the dip directions for the ultracataclasite zones are approximately tangential to the peak ring. These two orientations are consistent with deformation expected from hydrocode-modeled principal stress directions for the outward movement of rocks as the transient crater develops, and the inward movement of rocks associated with collapse of the transient crater. Near the base of the core is a 96 m-thick interval of highly-deformed target rock with impact melt rock and rock fragments not observed elsewhere in the core; this interval has previously been interpreted as an imbricate thrust zone within the peak ring. The cataclasite zones below this thrust zone have different orientations than those in the 470 m-thick block above. This observation implies a differential rotation from the overlying block during the final stages of peak-ring formation. Our results support an acoustic fluidization process, wherein blocks that vibrate or slide relative to each other allow the target rock to flow during transient crater collapse, and that the size of coherent rock blocks increases over the course of crater modification as the target rock regains its cohesive strength and acoustic fluidization decreases.

Progressive aqueous alteration and iron oxidation record in the matrix of Mukundpura CM2 chondrite, a new fall

1Ray D.,1Baliyan S.,2Nayak C.
Advances in Space Research 68, 3233-321 Link to Article [DOI 10.1016/j.asr.2021.06.009]
1Planetary Sciences Division, Physical Research Laboratory, Ahmedabad, 380 009, India
2Atomic & Molecular Physics Division, Bhabha Atomic Research Centre, Mumbai, 400085, India

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Shock-Induced Incongruent Melting of Olivine in Kamargaon L6 Chondrite

1Tiwari K.,1Ghosh S.,2Miyahara M.,3Ray D.
Geophysical Research Letters 48, e2021GL093592 Link to Article [DOI 10.1029/2021GL093592]
1Department of Geology and Geophysics, Indian Institute of Technology Kharagpur, Kharagpur, India
2Graduate School of Advanced Science and Engineering, Hiroshima University, Hiroshima, Japan
3Planetary Sciences Division, Physical Research Laboratory, Ahmedabad, India

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High Temperature Evaporation and Isotopic Fractionation of K and Cu

1Mason Neuman,1,2Astrid Holzheid,1Katharina Lodders,1Bruce FegleyJr.,1Bradley L.Jolliff,1Piers Koefoed,3Heng Chen,1Kun Wang王昆
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.09.035]
1Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA
2Institute of Geosciences, Kiel University, 24098 Kiel, Germany
3Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA
Copyright Elsevier

The chemical and isotopic signatures of moderately volatile elements are useful for understanding processes of volatile depletion in planetary formation and differentiation. However, the fractionation factors between gas and melt phases during evaporation that are required to model these planetary volatile depletion processes are still sparse. In this study, twenty heating experiments were conducted in 1 atm gas-mixing furnaces to constrain the behavior of K, Cu, and Zn evaporation and isotopic fractionation from basaltic melts at high temperatures. The temperatures range from 1300 °C to 1400 °C, and durations are from 2 to 8 days. Oxygen fugacities (fO2) range from one log unit below to ten log units above that of the iron-wüstite buffer (IW–1 to IW+10, corresponding to logfO2 of –10.7 to –0.68 at 1400 °C). The conditions were selected to achieve an evaporation-dominated regime (where timescales of diffusion << evaporation for trace elements) in order to avoid diffusion-limited evaporation. Our results show during evaporation Zn behaved as the most volatile, followed by Cu and then K, regardless of temperature and oxygen fugacity. Partitioning of Zn into spinel layers within experimental capsules, however, has been observed, which has substantial effects on the Zn isotope fractionation factor. Therefore, Zn results are presented but further discussion is excluded. Element loss depends on both temperature and oxygen fugacity, where higher temperatures and lower oxygen fugacities promote evaporation. However, with varying temperature and oxygen fugacity, the kinetic isotopic fractionation factors, α (where, RR0=fα-1), for K and Cu remain constant, thus these factors can be applied to a wider range of conditions than those in this study. The experimentally determined fractionation factors for K, and Cu during evaporation from basaltic melts are 0.9944, and 0.9961, respectively. The fractionation factors for these elements with varying volatilities are all significantly larger than the “apparent observed fractionation factors,” which approach one and are inferred from lunar basalts relative to the Bulk Silicate Earth. This observation suggests near-equilibrium conditions during volatile-element loss from the Moon as the “apparent observed fractionation factors” of lunar basalts are similar for all three elements.

Impact-related crystallization and modification of small zircons in Apollo 15 and 16 impactites at 4.2 Ga

1Dennis Marcel Vanderliek,1Harry Becker,2Alexander Rocholl
Earth and Planetary Science Letters 576, 117216 Link to Article [https://doi.org/10.1016/j.epsl.2021.117216]
1Institut für Geologische Wissenschaften, Freie Universität Berlin, Malteserstraße 74-100, 12249 Berlin, Germany
2Deutsches GeoForschungsZentrum GFZn, Telegrafenberg, D-14473 Potsdam, Germany
Copyright Elsevier

Because of their robustness against resetting, in situ U-Pb ages of zircons in lunar impactites have the potential to provide constraints on the lunar bombardment history that may complement the more common K-Ar ages. Most previous work has focused on relatively large zircons that show growth zoning and ages were mostly interpreted as early igneous crystallization ages. Here we combine high-resolution mineralogical imaging and in situ U-Pb dating by ion microprobe to identify, characterize and date <20 μm size zircons in thin sections of lunar impact breccias. Several tens of grains of zircons of this size range were identified in thin sections of impactites from the Apollo 15 and 16 landing sites. Small zircons are more abundant in both noritic and evolved clinopyroxene, SiO2 or K-feldspar bearing lithologies compared to anorthositic bulk compositions. Both granular zircon aggregates and overgrowth on existing zircon or baddeleyite (in breccias 15455 and 67915) are interpreted to reflect high-temperature recrystallization of zircons or its high-temperature-pressure precursor phases, following shock heating events by impact. In contrast, conchoidal or poikilitic zircons <10 μm in Fe-Ni metal bearing noritic clasts or matrix (67915, 67955) crystallized in situ from impact melt. Most U-Pb ages of the 24 analyzed grains are either concordant or reverse discordant with 207Pb-206Pb ages ranging from 4.15 to 4.25 Ga. The small age range, combined with a large textural spectrum and the frequent presence of Fe-Ni metal suggest zircon crystallization from impact melt and recrystallization of pre-existing zirconium-bearing minerals by impact heating. Such ‘impact’ zircons with 4.2 Ga ages have now been reported from most Apollo landing sites, suggesting widespread formation and modification of zircons by basin-forming impacts at this time. The contrast between U-Pb zircon (predominantly 4.2 Ga) and K-Ar feldspar ages (predominantly 3.9 Ga) likely reflects resetting of the latter chronometer by impact heating.

Plagioclase alteration and equilibration in ordinary chondrites: Metasomatism during thermal metamorphism

1Jonathan A.Lewis,1,2Rhian H.Jones,1Adrian J.Brearley
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.10.004]
1Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA
2Department of Earth and Environmental Sciences, University of Manchester, Manchester, M13 9PL, UK
Copyright Elsevier

In ordinary chondrites (OCs), feldspar is present both in chondrules as a primary, igneous phase, and as a secondary phase that results from crystallization of chondrule mesostasis glass during thermal metamorphism. To further understand the chemical and physical conditions prevailing during thermal metamorphism in OCs, we conducted a study of feldspar microtextures and compositions within chondrules, focusing on alteration and equilibration features. We included OCs representing the full metamorphic sequence (petrologic types 3-6) and all OC groups (H, L and LL). Our observations show that primary calcic plagioclase alters to sodalite, scapolite, and nepheline in petrologic types 3.2-3.9, and to albite in types 3.6-5. Plagioclase also develops alteration features such as zoning, micropores, and alteration lamellae in types 3-4. Sodic plagioclase is present in minor amounts as a primary phase, but also forms from the crystallization of chondrule mesostasis glass (types 3.2-3.9), and predominantly through albitization reactions in calcic plagioclase (types 3.6-5). K-feldspar occurs in albite in types 3.6-6 as fine-scale exsolution lamellae and as larger patches.

We combine these observations into an overall model of metasomatism during thermal metamorphism in OCs. Hydrous alteration during prograde metamorphism results in most of the alteration and equilibration features we observe in plagioclase. During retrograde metamorphism, high temperature, short duration infiltration of anhydrous, alkali- and halogen-bearing fluids causes incorporation of K into plagioclase that subsequently exsolves. Overall, we show that evidence of metasomatism is present throughout the metamorphic sequence in all the OCs, and thus was a ubiquitous process on all OC parent bodies. Recognition of the effects of fluid activity in OCs of even the lowest petrologic subtypes has important consequences for radioisotope chronometers, such as Al-Mg and I-Xe, that rely on the integrity of phases such as plagioclase and feldspathic mesostasis glass which are highly susceptible to alteration. Furthermore, the presence of aqueous alteration features in OCs implies that the non-carbonaceous chondrite isotopic reservoir must have also had ices and that models of protoplanetary disk evolution must also include the presence of ices in the inner solar system.

Geochemical Characterization of the NWA 11273 Lunar Meteorite Using Nondestructive Analytical Techniques: Original, Shocked, and Alteration Mineral Phases

1Huidobro J.,1Aramendia J.,1Arana G.,1Madariaga J.M.
ACS Earth and Space Chemistry 5, 1333 – 1342 Link to Article [DOI 10.1021/acsearthspacechem.0c00329]
1Analytical Chemistry Department, University of the Basque Country (UPV/EHU), Barrio Sarriena s/n, Leioa, 48980, Spain

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