^1,2K. K. Brugman,^1,3M. G. Phillips,¹C. B. Till
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2020JE006731]
¹School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
²Earth & Planets Laboratory, Carnegie Institution for Science, Washington, D.C. USA
³United States Geological Survey, Moffett Field, CA USA
Published by arrangement with John Wiley & Sons

For rocky exoplanets, knowledge of their geologic characteristics such as composition and mineralogy, surface recycling mechanisms, and volcanic behavior are key to determining their suitability to host life. Thus, determining exoplanet habitability requires an understanding of surface chemistry, and understanding the composition of exoplanet surfaces necessitates applying methods from the field of igneous petrology.

Piston-cylinder partial melting experiments were conducted on two hypothetical rocky exoplanet bulk silicate compositions. HEX1, a composition with molar Mg/Si = 1.42 (higher than bulk silicate Earth’s Mg/Si = 1.23) yields a solidus similar to that of Earth’s undepleted mantle. However, HEX2, a composition with molar Ca/Al = 1.07 (higher than Earth Ca/Al = 0.72) has a solidus with a slope of ∼10°C/kbar (versus ∼15°C/kbar for Earth) and as result, has much lower melting temperatures than Earth. The majority of predicted adiabats point toward the likely formation of a silicate magma ocean for exoplanets with a mantle composition similar to HEX2. For adiabats that do intersect HEX2’s solidus, decompression melting initiates at pressures more than 4x greater than in the modern Earth’s undepleted mantle. The experimental partial melt compositions for these exoplanet mantle analogs are broadly similar to primitive terrestrial magmas but with higher CaO, and for the HEX2 composition, higher SiO2 for a given degree of melting.

This first of its kind exoplanetary experimental data can be used to calibrate future exoplanet petrologic models and predict volatile solubilities, volcanic degassing, and crust compositions for exoplanets with bulk compositions and ƒO2 similar to those explored herein.

^1,2Amanda A.Tosi,²Maria Elizabeth Zucolotto,³Wania Wolff,¹Julio C.Mendes,⁴Sergio Suárez,^5,6Pablo Daniel Pérez,⁷Diana P.P.Andrade
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2021.105250]
¹LABSONDA/IGEO/UFRJ, Instituto de Geociências, Universidade Federal do Rio de Janeiro, Av. Athos da Silveira Ramos, 274, Cidade Universitária, 21941-972, Rio de Janeiro, RJ, Brazil
²LABET/MN/UFRJ, Laboratório Extraterrestre, Departamento de Geologia e Paleontologia, Museu Nacional, Universidade Federal do Rio de Janeiro, Quinta da Boa Vista, São Cristóvão, 20940-040 Rio de Janeiro, RJ, Brazil
³Instituto de Física, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil
⁴Divisiones Atômicas, Centro Atomico Bariloche (CONICET), Av. Bustillo 10000, San Carlos de Bariloche, Argentina
⁵Departamento de Ciencias Físicas, Universidad de La Frontera (UFRO), Temuco, Chile
⁶Centro de Física e Ingeniería en Medicina (CFIM), Universidad La Frontera (UFRO), Temuco, Chile
⁷Observatório do Valongo, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil

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

^1,2E.J.Allender,¹C.R.Cousins,²M.D.Gunn,¹E.R.Mare
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114541]
¹University of St Andrews, School of Earth and Environmental Sciences, Irvine Building, St Andrews KY16 9AL, UK
²Aberystwyth University, Department of Physics, Penglais Campus, Aberystwyth SY23 3BZ, UK
Copyright Elsevier

A key goal of the ExoMars rover Rosalind Franklin is to analyze accessible hydrated mineral deposits using panoramic multiscale and multispectral imagery. We conducted a multiscale spectroscopic study on hydrothermally-altered basalt-hosted soils in the geothermal area of Námafjall in northern Iceland. Basaltic lavas here that have experienced first-order geochemical alteration produce a variety of cm-to-meter scale poorly-crystalline alteration patterns. The resulting unconsolidated sediments provide a natural analogue material to investigate intimately mixed soils comprising multiple poorly-crystalline hydrated phases. We use emulator instruments which replicate the capabilities of the ExoMars 2022 Panoramic Camera (PanCam), the Infrared Spectrometer for ExoMars (ISEM), and the CLose-UP Imager (CLUPI), alongside Raman, aerial, and X-Ray Fluorescence spectroscopic data to investigate how the detection of these mixed basalt-derived alteration phases varies as a function of spatial and spectral scale. We find soils at our study site to be comprised of unconsolidated sediments including Al-OH minerals, hydrated silica, and a variety of ferric oxides, all of which Rosalind Franklin will likely encounter along its traverse at Oxia Planum. We report on (i) the synergy and limitations between Mars rover instrument emulators as an integral part of mission preparation, (ii) how the mixed nature of these hydrothermally-altered soils affects resulting mineralogical interpretations at multiple scales, and (iii) geochemical inferences that can be made using ExoMars 2022 imaging emulators.

¹Marco Veneranda et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114542]
¹University of Valladolid, Ave. Francisco Vallés, 8, 47151 Valladolid, Spain
Copyright Elsevier

This work presents the latest chemometric tools developed by the RLS science team to optimize the scientific outcome of the Raman system onboard the ExoMars 2022 rover. Feldspar, pyroxene and olivine samples were first analyzed through the RLS ExoMars Simulator to determine the spectroscopic indicators to be used for a proper discrimination of mineral phases on Mars. Being the main components of Martian basaltic rocks, lepidocrocite, augite and forsterite were then used as mineral proxies to prepare binary mixtures. By emulating the operational constraints of the RLS, Raman datasets gathered from laboratory mixtures were used to build external calibration curves. Providing excellent coefficients of determination (R2 0.9942÷0.9997), binary curves were finally used to semi-quantify ternary mixtures of feldspar, pyroxene and olivine minerals. As Raman results are in good agreement with real concentration values, this work suggests the RLS could be effectively used to perform semi-quantitative mineralogical studies of the basaltic geological units found at Oxia Planum. As such, crucial information about the geological evolution of Martian Crust could be extrapolated. In light of the outstanding scientific impact this analytical method could have for the ExoMars mission, further methodological improvements to be discussed in a dedicated work are finally proposed.

^1,2K.L.Villalon,³K.K.Ohtaki,³J.P.Bradley,³H.A.Ishii,^1,2,4A.M.Davis,^1,2T.Stephan
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.05.041]
¹Department of the Geophysical Sciences, The University of Chicago, Chicago, IL, USA
²Chicago Center for Cosmochemistry, University of Hawai‘i at Mānoa, Honolulu, HI, USA
³Hawai‘i Institute of Geophysics & Planetology, University of Hawai‘i at Mānoa, Honolulu, HI, USA
⁴Enrico Fermi Institute, The University of Chicago, Chicago, IL, USA
Copyright Elsevier

Amorphous silicates containing abundant nano-inclusions have been reported in the Paris CM chondrite (Leroux et al., 2015). They have chemical and morphological similarities to glass with embedded metal and sulfides (GEMS) found in interplanetary dust particles (IDPs) and micrometeorites believed to originate from comets. We used scanning transmission electron microscopy (STEM) with energy-dispersive X-ray spectroscopy (EDS) and nanodiffraction to study the chemistry and mineralogy of these inclusions in order to understand the origin of the GEMS-like material in Paris and its possible relationships to other materials found in primitive chondritic materials including IDP GEMS. EDS and diffraction analyses indicate compositional and mineralogical differences between the nanophase inclusions in cometary GEMS and Paris GEMS-like material. Metal inclusions are notably absent within Paris amorphous silicate. Ni-rich sulfides, including pentlandite, are common in even the least altered matrix material of Paris, while they are absent in GEMS-bearing IDPs and Ultracarbonaceous Antarctic Micrometeorites (UCAMMs). From examination of the inclusions, we cannot yet confirm or refute the possibility that GEMS-like material in Paris is related to cometary GEMS. The distinct compositions and mineralogy of the Paris material may be due to aqueous alteration of cometary GEMS precursors, but they may also denote an independent origin for meteoritic GEMS-like assemblages.

^1,2Gavin G.Kenny,²Claire O.Harrigan,²Mark D.Schmitz,²James L.Crowley,²Corey J.Wall,³Marco A.G.Andreoli,³Roger L.Gibson,⁴Wolfgang D.Maier
Earth and Planetary Science Letters 567, 117013 Link to Article [https://doi.org/10.1016/j.epsl.2021.117013]
¹Department of Geosciences, Swedish Museum of Natural History, SE-104 05 Stockholm, Sweden
²Isotope Geology Laboratory, Department of Geosciences, Boise State University, 1910 University Drive, Boise, ID 83725, USA
³School of Geosciences, University of the Witwatersrand (WITS), Johannesburg, South Africa
⁴School of Earth and Ocean Sciences, Cardiff University, Park Place, Cardiff CF10 3AT, UK
Copyright Elsevier

Impact cratering was a fundamental geological process in the early Solar System and, thus, constraining the timescales over which large impact structures cool is critical to understanding the thermal evolution and habitability of early planetary crusts. Additionally, impacts can induce mass extinctions and establishing the precise timing of the largest impacts on Earth can shed light on their role in such events. Here we report a high-precision zircon U–Pb geochronology study of the Morokweng impact structure, South Africa, which appears to have a maximum present-day diameter of ∼80 km. Our work provides (i) constraints on the cooling of large impact melt sheets, and (ii) a high-precision age for one of Earth’s largest impact events, previously proposed to have overlapped the ca. 145 Ma Jurassic–Cretaceous (J–K) boundary. High-precision U–Pb geochronology was performed on unshocked, melt-grown zircon from five samples from a borehole through approximately 800 m of preserved impact melt rock. Weighted mean 206Pb/238U dates for the upper four samples are indistinguishable, with relative uncertainties (internal errors) of better than 20 ka, whereas the lowermost sample is distinguishably younger than the others. Thermal modeling suggests that the four indistinguishable dates are consistent with in situ conductive cooling of melt at this location within 30 kyr of the impact. The younger date from the lowest sample cannot be explained by in situ conductive cooling in line with the overlying samples, but the date is within the ∼65 kyr timeframe for melt-present conditions in footwall rocks below the impact melt sheet that is indicated by our thermal model. The Morokweng impact event is here constrained to 146.06 ± 0.16 Ma (2σ; full external uncertainty), which precedes current estimates of the age of the J–K boundary by several million years.

¹Laurette Piani,¹Yves Marrocchi,²Lionel G.Vacher,³Hisayoshi Yurimoto,⁴Martin Bizzarro
Earth and Planetary Science Letters 567, 117008 Link to Article [https://doi.org/10.1016/j.epsl.2021.117008]
¹Université de Lorraine, CNRS, CRPG, UMR 7358, Vandoeuvre les Nancy, France
²Laboratory for Space Sciences and the Department of Physics, Washington University in St. Louis, St. Louis, MO 63130, USA
³Department of Natural History Sciences, Faculty of Science, Hokkaido University, Sapporo, Japan
⁴StarPlan – Centre for Star and Planet Formation, GLOBE Institute, University of Copenhagen, Øster Voldgade 5-7, Copenhagen, DK-1350, Denmark
Copyright Elsevier

Chondrites are rocky fragments of asteroids that formed at different times and heliocentric distances in the early solar system. Most chondrite groups contain water-bearing minerals, attesting that both water-ice and dust were accreted on their parent asteroids. Nonetheless, the hydrogen isotopic composition (D/H) of water in the different chondrite groups remains poorly constrained, due to the intimate mixture of hydrated minerals and organic compounds, the other main H-bearing phase in chondrites. Building on our recent works using in situ secondary ion mass spectrometry analyses, we determined the H isotopic composition of water in a large set of chondritic samples (CI, CM, CO, CR, and C-ungrouped carbonaceous chondrites) and report that water in each group shows a distinct and unique D/H signature. Based on a comparison with literature data on bulk chondrites and their water and organics, our data do not support a preponderant role of parent-body processes in controlling the D/H variations among chondrites. Instead, we propose that the water and organic D/H signatures were mostly shaped by interactions between the protoplanetary disk and the molecular cloud that episodically fed the disk over several million years. Because the preservation of D-rich interstellar water and/or organics in chondritic materials is only possible below their respective sublimation temperatures (160 and 350–450 K), the H isotopic signatures of chondritic materials depend on both the timing and location at which their parent body formed.

¹Jakob Storz,²Thomas Ludwig,¹Addi Bischoff,²Winfried H.Schwarz,²Mario Trieloff
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.05.028]
¹Institut für Planetologie, WWU Münster, Wilhelm-Klemm-Str. 10, D-48149 Münster, Germany
²Institut für Geowissenschaften, Klaus-Tschira-Labor für Kosmochemie, Universität Heidelberg, Im Neuenheimer Feld 234-236, D-69120 Heidelberg, Germany
Copyright Elsevier

Carbon is of fundamental interest for constraining the volatile element inventory of terrestrial planets. In some meteorites, like ureilites and enstatite chondrites, graphite is the major carbon-carrier. Here, we report the in-situ analyses of graphite in 19 ureilites, 11 enstatite chondrites, and 3 graphite-bearing clasts in ordinary chondrites by secondary ion-mass spectrometry (SIMS). In coarse-grained ureilites the obtained carbon-compositions of graphite range from –9.2‰ to –0.1‰ (δ13C). The carbon-composition tends to be homogeneous within a sample and correlates with the Fa content in olivine. In contrast, fine-grained ureilites exhibit considerable intra-sample heterogeneity, and graphite tends towards 13C-enriched compositions (up to +10.4‰). Isotopic and petrographic differences are presumably a result of post-igneous shock processing, including annealing during impact smelting. Enstatite chondrites host a variety of graphite morphologies, occurring in two distinct assemblages: Silicate-associated graphite (SAG) and metal-associated graphite (MAG). These assemblages show diverging carbon-compositions: SAG consistently exhibits δ13C in a narrow range between –4‰ to 1‰, very similar to the bulk silicate Earth value. In contrast, diverse compositions from –19.7‰ to +13.7‰ were observed for MAG. These differences are likely pre-accretionary in origin and potentially point towards isotopically distinct precursors. If Earth accreted from enstatite-chondrite-like material, carbon potentially hosted by Earth́s core may have an isotopically light signature when compared to the mantle. Although graphite-bearing clasts in unequilibrated ordinary chondrites (UOCs) are extraordinarily rare, these clasts are of particular interest as they might represent materials, not corresponding to known meteorites. Graphite from these clasts show coinciding carbon-compositions with a mean δ13C close to

–1‰. Although the coinciding compositions might argue for a genetic relationship among the clasts, petrographic evidence suggests they have experienced distinct thermal histories.

¹YunhuavWu,²徐伟彪(Weibiao Hsu),³Qiu-Li Li,⁴Xiaochao Che,²Shiyong Liao
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.05.011]
¹Planetary Environmental and Astrobiological Research Laboratory, School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai 519082, China
²CAS Center for Excellence in Comparative Planetology, Purple Mountain Observatory, Nanjing 210034, China
³State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
⁴Beijing SHRIMP Center, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 102206, China
Copyright Elsevier

Shergottites were derived from mantle reservoirs through various magmatic processes, recording geochemical signatures of the martian mantle. But the U-Pb isotopic system of shergottites remains obscured including the geological significance of Pb isotope composition, the role of martian Pb contamination, and other factors. Here we present in situ U-Pb and/or Pb-Pb analyses on minerals of the basaltic shergottite Northwest Africa (NWA) 8653 after detailed petrological and mineralogical studies. The aims of the project are to evaluate the formation process, the crystallization age as well as the characteristic Pb isotope composition of NWA 8653. Texture, major and trace element composition plus geochemical modeling suggest that NWA 8653 is an enriched shergottite derived from mixing of depleted (e.g., fractionated Yamato 980459) and enriched components (e.g., NWA 1068) in the mantle, instead of crustal assimilation. U-Pb and Pb-Pb isotopes of baddeleyite reveal a young crystallization age (187.6 ± 8.0 Ma). Pb isotope compositions of maskelynite, feldspathic intergrowth, and the majority of phosphate cluster near the predicted initial Pb and a 4.1 Ga isochron. For these minerals, calculations suggest that mixing of Pb from different reservoirs with μ (238U/204Pb) varying from 1.4 to 4.7 could explain the apparent 4.1 Ga isochron in young shergottites. Variable extents of mixing among mantle sources could further increase the isotopic heterogeneity of shergottites. Our results demonstrate that NWA 8653 was derived from a heterogeneous mantle source in terms of trace element and isotope composition. Mixing of Pb from different reservoirs in the mantle plays an important role in shaping Pb in minerals with negligible U. This study provides additional geochemical evidence for a highly heterogeneous martian mantle.

¹Makiko K. Haba,²Keisuke Nagao
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13660]
¹Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Ookayama, Tokyo, 152-8551 Japan
²Korea Polar Research Institute, 26 Songdomirae-ro, Yeonsu-gu, Incheon, 21990 South Korea
Published by arrangement with John Wiley & Sons

Zirconium produces cosmogenic Kr through spallation reactions with cosmic rays. Meteoritic zircons (ZrSiO4) therefore possibly contain a significant amount of cosmogenic Kr in addition to other cosmogenic nuclides. Detection of cosmogenic nuclides from meteoritic zircons would make it possible to determine precise cosmic ray exposure (CRE) ages without knowing the whole rock chemistry because of the robust nature of zircons and limited target elements that produce cosmogenic nuclides in a zircon crystal. Herein, we report the noble gas compositions of zircons separated from the Estherville mesosiderite in addition to those of the silicate and metal parts. The zircons contain cosmogenic noble gas nuclides, and more importantly, cosmogenic 81Kr (t1/2 = 2.29 × 105 years) was successfully detected in the zircons. The 81Kr-Kr exposure age of the zircons was calculated to be 76 ± 5 million years (Ma). This age corresponds to the CRE ages obtained from cosmogenic 3He and 21Ne (82 ± 8 and 88 ± 9 Ma, respectively) of the silicate part and the previously reported 36Cl-36Ar age of the metal part (77 ± 9 Ma). The consistent CRE ages using different dating methods demonstrate that the 81Kr-Kr dating using meteoritic zircons is a new promising tool for determining the CRE age of meteorites. Moreover, based on the 81Kr-Kr age of the zircons, the production rates of cosmogenic 3He and 21Ne in a meteoritic zircon were estimated to be (15 ± 2) × 10−9 and (0.69 ± 0.04) × 10−9 cm3 STP g−1 Ma−1, respectively.