¹J. Vaubaillon,¹N. Rambaux,²S. Loehle,³P. Matlovic,³J. Tóth,⁴J.F. Mariscal
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115906]
¹IMCCE, Observatoire de Paris, PSL, Sorbonne Université, 77 Av. Denfert Rochereau, Paris, 75014, France
²High Enthalpy Flow Diagnostics Group, Institute of Space Systems, University of Stuttgart, Pfaffenwaldring 29, 70569 Stuttgart, Germany
³Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia
⁴LATMOS, 11, boulevard D’Alembert, 78280 Guyancourt, France
Copyright Elsevier

The high energy of meteoroid entering the Earth atmosphere presumably results in UV radiation. However, ground-based observations are impaired by the atmospheric absorption below 400 nm. Artificial meteors are produced in a high enthalpy wind tunnel, and observed with a [200–400] nm fiber-fed spectrometer in order to analyse for the first time the UV emission of meteors. Similarly to visible observations, several atomic lines of Fe and Mg are detected. Contrary to observations in the visible wavelength range, Si is also clearly detected in all tested samples. Carbon is not detected in atomic lines. As the strongest emission lines are detected between 220 and 330 nm, we recommend that future meteor dedicated space-based UV instruments focus on this particular wavelength interval.

^1,2,3A.I. Sheen,¹C.D.K. Herd,^4,5L.G. Staddon,⁵J.R. Darling,⁶W.H. Schwarz,^2,3K.T. Tait
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2023.12.002]
¹Dept. of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Canada
²Dept. of Natural History, Royal Ontario Museum, Toronto, ON, Canada
³Dept. of Earth Sciences, University of Toronto, Toronto, ON, Canada
⁴School of Earth and Environmental Sciences, University of St Andrews, St Andrews, UK
⁵School of the Environment, Geography and Geoscience, University of Portsmouth, Portsmouth, UK
⁶Institute of Earth Sciences, Heidelberg Ion Probe, Heidelberg University, Heidelberg, Germany
Copyright Elsevier

Baddeleyite (monoclinic zirconia; m-ZrO2) occurs as a late-stage accessory mineral in shergottites and has been used to determine U–Pb igneous crystallization ages via in-situ secondary ion mass spectrometry (SIMS). During shergottite ejection from the surface of Mars, baddeleyite develops a range of microstructures primarily due to a series of shock-induced transformations to high pressure and temperature polymorphs. It remains poorly constrained to what extent U–Pb systematics in baddeleyite are sensitive to shock conditions experienced by shergottites. To investigate this, we examined baddeleyite in the enriched shergottites Jiddat al Harasis (JaH) 479, Northwest Africa (NWA) 10299, and NWA 12919, which bridge the gap in shock conditions represented in previous microstructural studies. Electron backscatter diffraction (EBSD) analysis reveals that although some baddeleyite grains retain magmatic microstructures (i.e. homogenous crystallographic orientations and twinning of igneous origin), there is widespread phase transformation to high-pressure orthogonal polymorphs (o-ZrO2) followed by reversion. JaH 479 contains more grains with preserved magmatic microstructures than the other two shergottites, suggesting that it experienced lower bulk shock pressures. Nanometer-scale reverted m-ZrO2 in NWA 10299 and NWA 12919 further points to insufficient post-shock temperatures; this contrasts with JaH 479 where greater variation in local temperature conditions enabled the development of µm-scale domains of reverted m-ZrO2. Individual grains that are separated into two distinct microstructural domains may reflect controls on shock propagation due to relative density contrast among the surrounding phases.

SIMS U–Pb baddeleyite analysis yields igneous crystallization ages of 210 ± 9 Ma (JaH 479), 196 ± 11 Ma (NWA 10299), and 188 ± 11 Ma (NWA 12919). At the SIMS resolution, we find no clear evidence for significant Pb loss in the surveyed baddeleyite grains, suggesting that temperatures during the formation of both nm-scale and µm-scale reverted m-ZrO2 in the three shergottites were insufficient to cause significant Pb diffusion. Given the robust baddeleyite U–Pb isotope systematics in the majority of shergottites dated by SIMS methods thus far, we argue that shock conditions experienced by the bulk of shergottites were insufficient to introduce significant U–Pb isotopic mobility, which is limited to grains showing microstructural evidence for extensive post-shock heating and recrystallization. Our findings place new constraints on baddeleyite microstructural response to shock conditions of shergottite ejection and demonstrate that microstructural observations are critical when using baddeleyite as a chronometer in shocked planetary materials.

^1,4R. Skartlien,¹J.B. Kihle,²J. Larsen,³J.K. Eager-Nash,⁴T.L. Palmer,³T. Boxer,⁵S.J. Daines,³N.J. Mayne
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2023.115908]
¹Institute for Energy Technology, Instituttveien 8, Kjeller, 2007, Norway
²University of Oslo, Project Stardust, Department of Geosciences, Sem Sælands vei 1, Oslo, 0371, Norway
³The University of Exeter, Department of Physics and Astronomy, Exeter, EX4 4SB, Devon, UK
⁴Venabo Analytics, Kirkeveien 96, Fetsund, 1900, Norway
⁵The University of Exeter, Exeter, EX4 4PY, Devon, UK
Copyright Elsevier

Micrometeorites (MM) that undergo low heating could have provided a source of organic material to the Earth during the Archean (4-2.5 Ga ago) before life emerged, given that the density of interplanetary dust and larger grains were much higher than today. Amino acids are destroyed on atmospheric entry if the temperature rises above the pyrolysis temperature of few hundred degrees Celsius, depending on type of amino acid. A numerical study was carried out to obtain temperature statistics along relatively rare grazing angle trajectories in the Quaternary (modern) and Archean atmospheres to determine the probability of “cold capture” below pyrolysis temperatures. Effects of the thermospheric temperature and density was considered for the Quaternary atmosphere, and an extended hydrogen/helium envelope remnant from the protosolar nebula was considered for the Archean atmosphere.

An important result for the Archean is an elevated “cold capture” probability (twice the capture probability in the modern atmosphere, up to 7%–8%) for low heating below 500 °C of small asteroidal grains around 20μm in diameter, and geocentric velocities in the range 3–5 km/s, provided that there was a remnant envelope. Cometary 20μm grains of higher geocentric velocities did not have such an elevated capture probability. If the Archean atmosphere did not have an envelope, it was found that these capture probabilities were lower than for the modern atmosphere for both cometary and asteroidal grains, due to smaller density scale height of the lower Archean atmosphere leading to faster heating rate. Radiative degradation of amino acids in these relatively small grains should be considered more closely since the X-ray and XUV-flux from the Sun was larger by a factor of about 5–10 in the Archean.

Very low maximum temperatures was found for 20μm asteroidal and cometary grains in the Quternary atmosphere, with temperatures in the range 150–200 °C, but with a very small capture probability in this range of typically less than 0.3%. All 300μm asteroidal grains were heated to temperatures above 500 °C for all atmosphere models. The probability of heating to temperatures < 500 °C of 100μm asteroidal grains, was estimated to 0.3% or less for all models. Most 100μm cometary grains were heated to temperatures > 500 °C for all models.

¹S. Narendranath,^1,2Netra S. Pillai,³M. Bhatt,¹K. Vadodariya,¹Radhakrishna Vatedka,^1,4Srikar P. Tadepalli,¹A. Sarwade,¹A. Tyagi,¹V. Sharan
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115898]
¹U R Rao Satellite Centre, ISRO., ISITE Campus, Bengaluru, 560035, India
²Centre for Earth Sciences, IISc, Bengaluru, Karnataka, India
³Physical Research Laboratory, Ahemadabad, Gujarat, India
⁴IIT, Banaras Hindu University, Varanasi, Uttar Pradesh, India
Copyright Elsevier

The distribution of Mg, Al, Si, Ca and Fe on the lunar surface are important to understand the petrological characteristics of the Moon and its geological evolution. We derived new elemental distribution maps using the Chandrayaan-2 Large Area Soft X-ray Spectrometer (CLASS) experiment onboard the Chandrayaan-2 Orbiter. These are the first set of maps derived from three years of CLASS data (2019-2022) at a spatial resolution of 150 km x 12.5 km. These maps are free of the topographic shadow effects and space weathering effects because the elemental abundances are derived only using X-ray spectra in the 0.5 to 20 keV energy range. CLASS derived abundances are compared to the elemental maps obtained using the Lunar Prospector Gamma Ray Spectrometer, with abundances of the lunar soil samples, and with XRF measurements of Chandrayaan-1 mission to establish its credibility. These maps derived using X-ray fluorescence spectroscopy are a new resource for lunar geochemical studies based on the most direct detection technique.

^1,2C. Royer,³S. Bernard,³O. Beyssac,³E. Balan,⁴O. Forni,³M. Gauthier,³M. Morand,³Y. Garino,³P. Rosier
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115894]
¹LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, Meudon, France
²Purdue University Earth, Atmospheric and Planetary Sciences department, West Lafayette, IN, USA
³Institut de Minéralogie, Physique des Matériaux et Cosmochimie, CNRS UMR 7590, Muséum National d’Histoire Naturelle, Sorbonne Université, Paris, France
⁴IRAP, CNRS, Université de Toulouse, UPS-OMP, Toulouse, France
Copyright Elsevier

Perseverance is on Mars, collecting samples which will inform about Martian paleoenvironmental conditions. However, the surface of Mars is continuously bombarded by ionizing radiation, including UVs, which may significantly alter hydrated mineral phases such as sulfates, phosphates and carbonates. To explore and constrain this effect, we experimentally exposed pellets of more or less hydrated minerals to UV radiation within a Martian chamber at a temperature relevant for the rocks at the surface of Mars. Results show that exposure to UV leads to a strong alteration of the Raman and IR signals of sulfates, phosphates and carbonates. The strong increase of the luminescence signals coupled to the decrease of the Raman signals relatively to the background and the clear attenuation of the IR signals are interpreted as caused by an increasing concentration of electronic defects. The present results have strong implications for the ongoing exploration of Mars: one should not expect to detect pristine materials, except over freshly excavated surfaces. Still, as a precaution, all the targets measured or collected on Mars should be considered as having been exposed to UV radiation to some extent.

¹D.L. Laczniak,¹M.S. Thompson,²R. Christoffersen,³C.A. Dukes,⁴R.V. Morris,⁴L.P. Keller
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115883]
¹Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN 47907, United States of America
²Jacobs, NASA Johnson Space Center, Mail Code X13, Houston, TX 77058, United States of America
³Laboratory for Astrophysics and Surface Physics, University of Virginia, 395 McCormick Road, Charlottesville, VA 22904, United States of America
⁴ARES, Mail Code X13, NASA Johnson Space Center, Houston, TX 77058, United States of America
Copyright Elsevier

We present results from a set of low and high flux 1 keV/amu H+ and He+ irradiation experiments performed on slabs of the Murchison CM2 carbonaceous chondrite. The low flux conditions for H+ and He+ irradiation were ~ 1–1.5 orders of magnitude lower than the high flux conditions, and each experiment was irradiated to a total fluence between ~3 × 1016 to ~6 × 1016 ions/cm2. Irradiation-induced changes in the surface chemistry and optical properties of the Murchison samples were evaluated using in situ X-ray photoelectron spectroscopy (XPS) and visible and near-infrared spectroscopy (VNIR). We characterized the microstructure and composition of ion damaged rims in focused ion beam (FIB) cross-sections extracted from olivine and matrix material in each irradiated Murchison slab using transmission electron microscopy (TEM). XPS results suggest that both low flux and high flux H+ and He+ irradiation cause minor sputtering of surface carbon as well as a reduction in the valence state of iron, from Fe3+ to Fe2+. Slope bluing is observed in VNIR spectra of the irradiated samples which may reflect carbonization and dehydrogenation of organic species and contrasts with reddening trends associated with npFe0 formation. Although we do not observe a strong flux-dependence on the crystallinity of ion-damaged olivine, TEM analyses reveal a variety of microstructures in all olivine FIB-sections, suggesting that crystallographic orientation affects amorphization efficiency. Analyses of matrix FIB-sections indicate that phyllosilicate alteration is mainly driven by He+ irradiation, where the higher incident flux leads to greater amorphization and the formation of more distinct ion-damaged layers, similar to smooth layers in returned Ryugu particles. TEM results also provide some evidence that higher ion flux leads to greater vesiculation, with He+ irradiation being more efficient at vesiculation than H+ irradiation, and that higher ion flux may promote the segregation of Mg and Si into laterally extensive lenses and layers in olivine samples. We discuss the implications of these findings for constraining the role that ion flux plays in the development of space weathering characteristics in silicate phases present in carbonaceous asteroidal regoliths. These results will be important for understanding the complexity of this process and how it operates on carbon-rich airless bodies like asteroids Bennu and Ryugu.

¹L. F. Adam,¹J. C. Bridges,²C. C. Bedford,¹J. M. C. Holt,³E. Rampe,⁴M. Thorpe,⁵K. Mason,⁵R. C. Ewing
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14105]
¹Space Park Leicester, School of Physics and Astronomy, University of Leicester, Leicester, UK
²Department of Earth, Atmospherics, and Planetary Sciences, Purdue University, West Lafayette, Indiana, USA
³NASA Johnson Space Center, Houston, Texas, USA
⁴NASA Goddard Space Flight Center, University of Maryland, Greenbelt, Maryland, USA
⁵Department of Geology and Geophysics, Texas A&M University, College Station, Texas, USA
Published by arrangement with John Wiley & Sons

The joint NASA-ESA Mars sample return campaign aims to return up to 31 sample tubes containing drilled sedimentary and igneous cores and regolith. The titanium alloy tubes will initially still be sealed when they are retrieved. Several types of measurement will be carried out on sealed samples in the pre-basic characterization phase of scientific investigation. We show that powder x-ray diffraction (XRD) analysis can be successfully carried out on sealed samples using an x-ray source at the I12 beamline of Diamond Light Source synchrotron. Our experiment used an analog sample tube and a Martian regolith analog (Icelandic basaltic sand). The titanium walls of the tube analog give strong but few diffraction peaks, making identification of the major constituent mineral phases feasible. A more significant constraint on quantification of mineral phase abundances by this XRD technique is likely to be the grain size of the sample. This technique opens up the possibility of initial mineralogical analysis of samples returned from Jezero crater without opening the sample tubes and the potential changes to the sample that entails.

¹Allan H. Treiman,²Julia Semprich
American Mineralogist 108, 2182-2192 Open Access Link to Article [http://www.minsocam.org/msa/ammin/toc/2023/open_access/AM108P2182.pdf]
¹Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, Texas 77058, U.S.A. 2
²AstrobiologyOU, School of Environment, Earth and Ecosystem Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, U.K.
Copyright: The Mineralogical Society of America

A centimeter-sized fragment of dunite, the first recognized fragment of Moon mantle material, has
been discovered in the lunar highlands breccia meteorite Northwest Africa (NWA) 11421. The dunite
consists of 95% olivine (Fo83), with low-Ca and high-Ca pyroxenes, plagioclase, and chrome spinel.
Mineral compositions vary little across the clast and are consistent with chemical equilibration. Mineral
thermobarometry implies that the dunite equilibrated at 980 ± 20 °C and 0.4 ± 0.1 gigapascal (GPa)
pressure. The pressure at the base of the Moon’s crust (density 2550 kg/m3) is 0.14–0.18 GPa, so the
dunite equilibrated well into the Moon’s upper mantle. Assuming a mantle density of 3400 kg/m3
, the dunite equilibrated at a depth of 88 ± 22 km. Its temperature and depth of equilibration are consistent with the calculated present-day selenotherm (i.e., lunar geotherm).
The dunite’s composition, calculated from mineral analyses and proportions, contains less Al, Ti,
etc., than chondritic material, implying that it is of a differentiated mantle (including cumulates from
a lunar magma ocean). The absence of phases containing P, Zr, etc., suggests minimal involvement
of a KREEP component, and the low proportion of Ti suggests minimal interaction with late melt
fractionates from a lunar magma ocean. The Mg/Fe ratio of the dunite (Fo83) is significantly lower
than models of an overturned unmixed mantle would suggest, but is consistent with estimates of the
bulk composition of the Moon’s mantle

¹J ZhangZhou,²Yuan Li,³Proteek Chowdhury,⁴Sayan Sen,^5,6Urmi Ghosh,²Zheng Xu,⁷Jingao Liu,⁸Zaicong Wang,⁹James M.D. Day
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2023.11.029]
¹Key Laboratory of Geoscience Big Data and Deep Resource of Zhejiang Province, School of Earth Sciences, Zhejiang University, Hangzhou, China
²State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
³Earth, Environment and Planetary Sciences, Rice University, TX 77005, USA
⁴Zuckerberg Institute for Water Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion 8499000, Israel
⁵Environmental and Biochemical Sciences, The James Hutton Institute, Craigiebuckler, Aberdeen AB15 8QH, UK
⁶Department of Geology and Geophysics, Indian Institute of Technology (IIT) Kharagpur, 721302 Kharagpur, India
⁷State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Beijing), Beijing, China
⁸State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China
⁹Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0244, USA
Copyright Elsevier

The sulfur content at sulfide saturation (SCSS) of a silicate melt can regulate the stability of sulfides and, therefore, chalcophile elements’ behaviors in planetary magma oceans. Many studies have reported high-pressure experiments to determine SCSS using either linear or exponential regressions to parameterize the thermodynamics of the system. Although these empirical equations describe the effects of different parameters on SCSS, they perform poorly when predicting laboratory measurements. Here, we compiled 542 published analyses of experiments performed on a range of sulfide and silicate compositions at varying P–T conditions (<24 GPa, <2673 K). Using empirical equations, linear regression, Random Forest algorithms, and a hybrid algorithm employing empirical fits to P–T conditions and the Random Forest algorithm for compositions, we developed several SCSS models and compared them to laboratory measurements. The Random Forest and hybrid models (R² = 0.82–0.91, mean average error [MAE] < 746 ppmw S, residual mean standard error [RMSE] < 972 ppmw S), significantly outperform previous empirical models (R² = 0.28–0.69, MAE = 622–1,170 ppmw S, RMSE = 1,070–1,744 ppmw S), whereas linear regression performs moderately well, i.e., between the classic and machine learning models. We applied our hybrid model to predict SCSS during magma ocean solidification on Earth, Mars, and the Moon, and we compared our model results to expected S contents in the residual magma oceans calculated by mass balance. Our results confirm that during early accretion, sulfides precipitated from magma oceans and into the outer cores of Earth and Mars, but not the Moon. Subsequently, once the respective magma oceans began precipitating minerals with increasingly FeO-rich and SiO₂-, Al₂O₃-, and MgO-depleted compositions, the increasing S concentration in the residual magma was offset by temperature and compositional effects on SCSS, preventing sulfide precipitation during intermediate stages of crystallization. Sulfides precipitated late during magma ocean crystallization, but failed to percolate through the underlying crystalline mantle, significantly contributing to the modern bulk-silicate sulfur abundances of Earth, Mars, and the Moon. Our calculations suggest that late-stage sulfide precipitation occurred at shallow depths of 120–220 km, 40–320 km, and <10 km in the magma oceans of Earth, Mars, and the Moon, respectively.

^1,2F. Jourdan,^1,2T. Kennedy,²L. Foreman,¹C. Mayers,³E. Eroglu,^4,5A. Yamaguchi
Geoochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2023.11.027]
¹Western Australian Argon Isotope Facility, John de Laeter Centre, TIGeR, Curtin University, Australia
²Space Science and Technology Centre, School of Earth and Planetary Sciences, Curtin University, Australia
³School of Molecular and Life Sciences, Curtin University, Australia
⁴National Institute of Polar Research, Tachikawa, Tokyo 190-8518, Japan
⁵Department of Polar Science, School of Multidisciplinary Science, SOKENDAI (The Graduate University for Advanced Studies), Tokyo 190-8518, Japan
Copyright Elsevier

In this study, we investigate the 40Ar/39Ar systematics of nineteen diogenites thought to come from deep crustal levels of asteroid 4 Vesta. We applied both Electron Backscattered Diffraction (EBSD) and 40Ar/39Ar and methods to the unbrecciated diogenite LAP 031381. We obtained three plateau ages resulting in a combined weighted mean age of 4441 ± 15 Ma (P = 0.16). The EBSD analyses suggest that LAP 031381 displays minimal evidence of shock and, when combined with petrography observations, diffusion modelling and 40Ar/39Ar data, these results suggest that the crustal volume that initially contained this diogenite, reached a temperature of ca. 630 °C at ∼ 4.44 Ga. This corresponds to a linear cooling rate of ∼ 5 °C / Ma for a crystallization age of 4550 Ma. Independent thermal models suggest that these conditions were present at a depth of 60 to 65 km at 4.44 Ga.

The other eighteen diogenites yielded 40Ar/39Ar results that indicate that they have been variously shocked by impact events and seven of them yielded plateau ages ranging from 2413 ± 189 Ma to 84 ± 162 Ma. We combined these results with 40Ar/39Ar ages from eucrites and howardites and propose that the HED (Howardite, Eucrite, Diogenite) meteorites recorded impact events at the surface of Vesta until ∼ 3.4 Ga when they were then ejected during a large collision. The eucrites, diogenites and howardites were then recombined into small rubble pile asteroids which probably make up a large part of the Vestoid family. After ejection, the K/Ar system in plagioclase crystals ceased in most cases to be fully reset by impact events as the temperature spikes reached during small impacts lack enough energy to trigger significant 40Ar* diffusion. On the other hand, ultra-transient and high-temperature – sensitive pyroxene crystals kept a more systematic record of small impacts until recent time. 38Arc cosmochron cosmogenic exposure ages on diogenites mostly range from 51 ± 7 Ma to 0 ± 1 Ma and when combined with other HED cosmochron ages, suggest that almost all the HED meteorites were continuously ejected from secondary rubble pile asteroids mostly between 50 Ma and present.