¹Steven W. Ruff,²Victoria E. Hamilton
Journal of Geophysical Research, Planets (in Press) Link to Articles [https://doi.org/10.1029/2021JE006822]
¹Arizona State University, School of Earth and Space Exploration
²Southwest Research Institute, Boulder, CO
Published by arrangement wíth John Wiley & Sons

Spectra from the Mars Global Surveyor Thermal Emission Spectrometer (TES) display a combination of features attributable to surface and atmospheric components. In order to fully recognize and interpret surface spectral features, the atmospheric spectral features must be removed through some form of surface-atmosphere separation (SAS). Multiple SAS techniques are available representing a range of complexity and accuracy. A ratio between spectra from a region of interest and a relatively spectrally bland, dusty location is an effective SAS technique, but the resulting ratio spectrum contains spectral features of surface dust from the dusty location. We exploit the uniform spectral character of surface dust across Mars to produce dust-removed ratio spectra (DRRS). This simple and robust technique allows TES spectra to be compared directly to laboratory spectra and to Mini-TES spectra from the Mars Exploration Rovers. Although previous SAS techniques yield atmospherically corrected spectra that can serve this purpose, they are more challenging to implement, retain fewer data points, and are less accurate in some cases. The DRRS technique provides an option that is well suited to both quick-look assessments of TES spectra and in-depth analyses using follow-on spectral modeling techniques. We show that DRRS of olivine -rich bedrock in the Nili Fossae region display spectral features that match olivine with a composition ranging from ∼Fo50 to

¹Alan E.Rubin
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13693]
¹Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California, 90095–1567 USA
²Maine Mineral & Gem Museum, 99 Main Street, P.O. Box 500, Bethel, Maine, 04217 USAM
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13693]
Published by arrangement with John Wiley & Sons

IIE irons were derived from chondritic precursors that were the most reduced ordinary chondrites. The bulk chemical (e.g., Ir/Ni, Ir/Au, Au/Ni, Co/Ni) and bulk isotopic (i.e., Δ17O and δ74/70Ge) compositions of IIE irons lie along extensions of LL-L-H trends. Chondrule-bearing silicate clasts in IIE irons have mineralogical and petrological characteristics that extend LL-L-H trends; these clasts have higher modal metallic Fe-Ni and lower values for olivine Fa, low-Ca-pyroxene Fs, kamacite Co, and mean chondrule diameter. IIE irons are modeled as agglomerating before H-L-LL chondrites; they acquired more 26Al and reached the Fe,Ni-FeS eutectic temperature (˜940 °C). An FeS-rich metallic melt separated from unmelted silicate and drained to the core, eventually generating a dynamo. Most IIE metal remained within the crust/mantle region alongside recrystallized chondritic clasts. Alkali-rich IIE silicate inclusions formed from late-stage impacts via preferential melting of plagioclase. Some separation of K from Na occurred during vapor transport. Because most type I chondrules formed before most type II chondrules, the (type I)/(type II) modal ratio decreased from IIE to H to L to LL during agglomeration. Earlier-formed chondrules acquired higher abundances of refractory metal nuggets within CAI-fragment precursors, accounting for systematic changes in bulk OC of refractory/common siderophile and refractory/volatile siderophile ratios (IIE>H>L>LL). Because more Au and Co than Ni were retained in silicates, loss of metal globules from spinning partly molten type I chondrules caused systematic whole-rock decreases in Au/Ni and Co/Ni from IIE through LL. Expelled globules had different nebular aerodynamic properties than chondrules and drifted away (accounting, in part, for the metal/silicate fractionation).

¹Martijn Klaver,^1,2Tu-Han Luu,¹Jamie Lewis,³Maximiliaan N.Jansen,⁴Mahesh Anand,⁵Johannes Schwieters,¹Tim Elliott
Earth and Planetary Science Letters 570, 117079 Link to Article [https://doi.org/10.1016/j.epsl.2021.117079]
¹Bristol Isotope Group, School of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol BS8 1RJ, United Kingdom
²Université de Paris, Institut de Physique du Globe de Paris. CNRS, F-75005 Paris, France
³School of Earth and Environmental Sciences, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, United Kingdom
⁴School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, United Kingdom
⁵Thermo-Fisher Scientific, Hannah-Kunath Strasse, Bremen, Germany
Copyright Elsevier

The Ca isotope compositions of mare basalts offer a novel insight into the heterogeneous nature of the lunar mantle. We present new high-precision Ca isotope data for a suite of low-Ti and high-Ti mare basalts obtained using our collision cell MC-ICP-MS/MS instrument, Proteus. Mare basalts were found to have a Ca isotope composition resembling terrestrial basalts (δ44/40Ca_{SRM 915a} =0.78–0.89‰) even though they are derived from a differentiated, refractory cumulate mantle source. Modelling of Ca isotope fractionation during crystallisation of a lunar magma ocean (LMO) indicates that the dominantly harzburgitic cumulates of the lunar interior should be isotopically heavier than Earth’s mantle (δ44/40Ca_{SRM 915a} =1.1–1.2‰ versus 0.93‰, respectively). These are balanced by an isotopically light lunar anorthosite crust, consistent with data for lunar anorthosite and feldspathic breccia meteorites.

We investigate the major element and Ca isotope composition of partial melts of various cumulate reservoirs by combining pMELTS models with equilibrium isotope fractionation mass balance calculations. The principal finding is that harzburgite cumulates alone are too refractory a source to produce low-Ti magmas. Partial melts of harzburgite cumulates have too low CaO contents, too high Al₂O₃/CaO and too high δ44/40Ca_{SRM 915a} to resemble low-Ti magmas. From Ca isotope constraints, we find that the addition of 10–15% of late-stage, clinopyroxenite cumulates crystallising at 95% LMO solidification is required to produce a suitable source that can generate low-Ti basalt compositions. Despite the addition of such late-stage cumulates pMELTS finds that these hybrid sources are undersaturated in clinopyroxene and are thus consistent with experimental constraints that the mantle sources of the lunar magmas are clinopyroxene-free. High-Ti basalts have slightly lower δ44/40Ca_{SRM 915a} (0.80–0.86‰) than low-Ti magmas (0.85–0.89‰) and clearly elevated TiO₂/CaO. No suitable hybrid source involving ilmenite-bearing cumulates (IBC) was found that could reproduce melts with appropriate δ44/40Ca and major element systematics. Instead, we suggest that metasomatism of low-Ti mantle sources by IBC melts is the most plausible way to generate high-Ti magma sources and the rich diversity in TiO₂ contents of lunar basalts and pyroclastic glasses.

¹Sergei Batovrin,¹Boris Lipovsky,²Yury Gulbin,³Yury Pushkarev,³Yury A. Shukolyukov
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13662]
¹Independent Researcher, 120 Casals Place, Bronx, New York, 10475 USA
²The Mining Institute of St. Petersburg, Vasilevsky ostrov, 21 Liniya, Dom 2, St. Petersburg, 199106 Russia
³Institute of Geology and Geochronology of Precambrian, RAS, Naberezhnaya Makarova 2, St. Petersburg, 199034 Russia
Published by arrangement with John Wiley & Sons

Terrestrially occurring iron silicide spherules, described in the geological literature for 160 years as cosmogenic and approved as “extraterrestrial” minerals by IMA CNMMN in 1984, so far have escaped any serious examination by meteoriticists. Our isotopic and REE data, obtained for silicide spherules for the first time, disagree with the meteoritic origin of gupeiite (Fe3Si) and xifengite (Fe5Si3) spherules from two continents. Despite departures from terrestrial norms (87Rb/86Sr—0.0174; 87Sr/86Sr—0.700181; 3He/4He—7.57 × 10−6; 40Ar/36Ar—325.9), the compositions of 143Nd/144Nd (0.512034) and 147Sm/144Nd (0.06357), as well as REE abundances, clarify provenance from upper crust sediments for samples with U/Pb age of 121–314 ka from the Ala-Tau range in the Urals. However, the morphology of flanged button shapes, ring waves, and eccentro-radiating ridges reliably constrains the origin of silicide spherules to distal meteoritic impact ejecta. Arc jet ablation experiments have previously demonstrated that similar morphologies, observed on australite tektites, reflect aerodynamic ablation rates corresponding to flight velocities well into orbital range. These features are generally accepted as conclusive evidence for hypervelocity atmospheric entry from space. Internal structure, consistent with accretion through the coalescence of 3–5 µm droplets, and composition, closely corresponding to 1893–1154 K span of C-type condensation sequences, indicate a high probability of processing through recondensation of ejecta vapor.

¹Yoko Kebukawa et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13713]
¹Department of Chemistry and Life Science, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama, 240-8501 Japan
Published by arrangement with John Wiley & Sons

The Almahata Sitta (AhS) meteorite is a unique polymict ureilite. Recently, carbonaceous chondritic lithologies were identified in AhS. Organic matter (OM) is ubiquitously found in primitive carbonaceous chondrites. The molecular and isotopic characteristics of this OM reflect its origin and parent body processes, and are particularly sensitive to heating. The C1 lithologies AhS 671 and AhS 91A were investigated, focusing mainly on the OM. We found that the OM in these lithologies is unique and contains primitive isotopic signatures, but experienced slight heating possibly by short-term heating event(s). These characteristics support the idea that one or more carbonaceous chondritic bodies were incorporated into the ureilitic parent body. The uniqueness of the OM in the AhS samples implies that there were large variations in primitive carbonaceous chondritic materials in the solar system other than known primitive carbonaceous chondrite groups such as CI, CM, and CR chondrites.

¹Mehmet Yesiltas,²Timothy D. Glotch,³Bogdan Sava
Scientific Reports 11, 11656 Link to Article [DOI https://doi.org/10.1038/s41598-021-91200-8]
¹Faculty of Aeronautics and Space Sciences, Kirklareli University, Kirklareli, Turkey
²Department of Geosciences, Stony Brook University, Stony Brook, NY, USA
³Neaspec GmbH, 85540, Haar, Munich, Germany

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

^1,2Claire I. O. Nichols,²James F.J. Bryson,³Rory D. Cottrell,⁴Roger R. Fu,¹Richard J. Harrison,^5,6Julia Herrero-Albillos,⁷Florian Kronast,³John A. Tarduno,⁴Benjamin P. Weiss
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2021JE006900]
¹Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Insitute of Technology, Cambridge, MA, 02139 USA
²Department of Earth Sciences, University of Oxford, Oxford, OX1 3AN UK
³Department of Earth and Environmental Sciences, University of Rochester, NY, 14627 USA
⁴Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
⁵Centro Universitario de la Defensa, Carretera de Huesca s/n, E-50090 Zaragoza, Spain
⁶Instituto de Nanociencia y Materiales de Aragón (INMA), CSIC—Universidad de Zaragoza, Zaragoza, 50009 Spain
⁷Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Strasse 15, 12489 Berlin, Germany
Copyright Elsevier

Several paleomagnetic studies have been conducted on five main group pallasites: Brenham, Marjalahti, Springwater, Imilac and Esquel. These pallasites have distinct cooling histories, meaning that their paleomagnetic records may have been acquired at different times during the thermal evolution of their parent body. Here we compile new and existing data to present the most complete time-resolved paleomagnetic record for a planetesimal, which includes a period of quiescence prior to core solidification as well as dynamo activity generated by compositional convection during core solidification. We present new paleomagnetic data for the Springwater pallasite, which constrains the timing of core solidification. Our results suggest that in order to generate the observed strong paleointensities ( ∼ 65 – 95 μT), the pallasites must have been relatively close to the dynamo source. Our thermal and dynamo models predict that the main group pallasites originate from a planetesimal with a large core (> 200 km) and a thin mantle (< 70 km).

¹M.Grott et al. (>10)
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2021JE006861]
¹German Aerospace Center (DLR), Institute of Planetary Research, Berlin, Germany
Published by arrangment with John Wiley & Sons

The heat flow and physical properties package (HP³) of the InSight Mars mission is an instrument package designed to determine the martian planetary heat flow. To this end, the package was designed to emplace sensors into the martian subsurface and measure the thermal conductivity as well as the geothermal gradient in the 0-5 m depth range. After emplacing the probe to a tip depth of 0.37 m, a first reliable measurement of the average soil thermal conductivity in the 0.03 to 0.37 m depth range was performed. Using the HP³ mole as a modified line heat source, we determined a soil thermal conductivity of 0.039 ± 0.002 W m⁻¹ K⁻¹, consistent with the results of orbital and in-situ thermal inertia estimates. This low thermal conductivity implies that 85 to 95 % of all particles are smaller than 104-173 μm and suggests that soil cementation is minimal, contrary to the considerable degree of cementation suggested by image data. Rather, cementing agents like salts could be distributed in the form of grain coatings instead. Soil densities compatible with the measurements are  kg m⁻³, indicating soil porosities of  %.

¹G.Alemanno,¹A.Maturilli,¹M.D’Amore,¹J.Helbert
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114622]
¹Institute for Planetary Research, German Aerospace Center DLR, Rutherfordstr. 2, 12489 Berlin, Germany
Copyright Elsevier

New spectral orbital thermal infrared data of Mars are being acquired by the thermal infrared channel TIRVIM (in honor of Vassily Ivanovich Moroz) of the Atmospheric Chemistry Suite (ACS) of spectrometers on board of ExoMars2016 mission. TIRVIM encompasses the spectral range of 1.7–17 μm. A major challenge brought by the analysis of these data of planetary bodies with atmospheres is the ability to extract from the data the relevant information about the surface. Thus, laboratory work plays an essential role, providing end-member and mixture spectral data of planetary analogs to fit the orbital data by means of deconvolution techniques. At the Planetary Spectroscopy Laboratory (PSL) of the German Aerospace Center (DLR), we are performing new laboratory experiments on Martian analogs in order to provide a new and updated library of spectra optimized for the interpretation of TIRVIM data. Emissivity measurements, recorded at increasing temperatures, are coupled with reflectance measurements on fresh and thermally processed samples acquired between 1.7 and 17 μm. Building on measurements previously collected on Martian analogues, we have paid particular attention to the study of the spectral behaviour of mixtures of carbonates and phyllosilicates. The main goal of this analysis is to study the variation of the main carbonate spectral features in mixtures with a phyllosilicate component, an important factor for understanding the story of carbonates detections on planetary surfaces and to provide insights for new detections. The results obtained in this work show that the presence of a phyllosilicate component affect the appearance of the carbonate spectral features in the spectral range studied, with a stronger effect in the range between 1.7 and 5 μm. Effects of mineral type and particle size are also investigated and shown to strongly affect the spectral behaviour of laboratory samples. Finally, deconvolution techniques of laboratory emissivity spectra are studied in preparation for the interpretation of atmospherically corrected TIRVIM spectral data, showing that modelled mixtures spectra represent an acceptable reproduction of laboratory spectra of mixtures.

^1,2M. Kimura,³R. C. Greenwood,⁴M. Komatsu,¹N. Imae,¹A. Yamaguchi,²R. Sato
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13704]
¹National Institute of Polar Research, Tokyo, 190-8518 Japan
²Ibaraki University, Mito, 310-8512 Japan
³The Open University, Milton Keynes, MK7 6AA UK
⁴SOKENDAI, Hayama, Kanagawa, 240-0193 Japan
Published by arrangement with John Wiley & Sons

Most carbonaceous (C) chondrites are classified into eight major groups: CI, CM, CO, CV, CK, CR, CH, and CB. However, some are ungrouped. We studied two such chondrites, Asuka (A)-9003 and A 09535. The abundance of chondrules and matrix and chondrule sizes in these meteorites are similar to those in ordinary chondrites and unlike any known carbonaceous chondrite group. In contrast, they contain 4–6 vol% of refractory inclusions and have oxygen isotopic compositions within the range of CO and CV chondrites. Therefore, A-9003 and A 09535 are classified as C chondrites. Petrologic subtypes of A-9003 and A 09535 are 3.2. All these features closely resemble those of another ungrouped chondrite, Yamato (Y)-82094, and differ from those of any C chondrites reported by now. A-9003, A 09535, and Y-82094 likely represent a new type of C chondrite. We provisionally call them CA chondrite after Asuka in Antarctica. Our study suggests a wider range of formation conditions for C chondrites than currently recorded by the major C chondrite groups.