¹J.P.Mason et al. (>10)
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2023JE008002]
¹School of Physical Sciences, The Open University, Milton Keynes, UK
Published by arrangement with John Wiley & Sons

Spectroscopic measurements are a powerful tool to investigate the surface composition of airless bodies and provide clues of their origin. The composition and origin of Phobos and Deimos are still unknown and are currently widely debated. We present spectroscopic measurements of Phobos and Deimos at ultraviolet and visible wavelengths (250–650 nm) made by the NOMAD-Ultraviolet and Visible Spectrometer (UVIS) on the ExoMars TGO mission. These new spectra cover multiple areas on Phobos and Deimos, and are of generally higher spectral resolution and signal-to-noise than previous spectra, and extend to lower wavelengths than most previous measurements. The UVIS spectra confirm a red-sloped spectrum lacking any strong absorption features; however, we confirm the presence of a previously identified absorption feature near 0.65 μm and tentative absorption near 0.45 μm. The observed Phobos and Deimos spectra are similar to D- and T-type asteroids, adding weight to the captured asteroid hypothesis for the moons’ origins. We also find, however, that the UVIS Phobos reflectance spectra of Phobos’ red unit is a relatively close match to the olivine-rich, highly shocked Mars meteorite NWA 2737, with a low overall reflectance, a red-sloped spectrum, and lack of olivine-associated absorption bands in the UVIS spectral range. This meteorite, however, exhibits spectral features at longer wavelengths that not observed in the Martian moon spectra, indicating a need for further investigation at longer wavelengths to interpret whether this material could inform our understanding of Phobos’ origin.

¹David Nesvorný,²Nicolas Dauphas,³David Vokrouhlický,¹Rogerio Deienno,⁴Timo Hopp
Earth and Planetary Science Letters 626, 118521 Link to Article [https://doi.org/10.1016/j.epsl.2023.118521]
¹Department of Space Studies, Southwest Research Institute, 1050 Walnut St., Suite 300, Boulder, CO 80302, United States
²Origins Laboratory, Department of the Geophysical Sciences, The University of Chicago, 5734 S. Ellis Avenue, Chicago, IL 60637, United States
³Institute of Astronomy, Charles University, V Holešovičkách 2, CZ-18000 Prague 8, Czech Republic
⁴Max Planck Institute for Solar System Research, Planetary Science Department, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
Copyright Elsevier

Recent analyses of samples from asteroid (162173) Ryugu returned by JAXA’s Hayabusa2 mission suggest that Ryugu and CI chondrites formed in the same region of the protoplanetary disk, in a reservoir that was isolated from the source regions of other carbonaceous (C-type) asteroids. Here we conduct N-body simulations in which CI planetesimals are assumed to have formed in the Uranus/Neptune zone at ∼15–25 au from the Sun. We show that CI planetesimals are scattered by giant planets toward the asteroid belt where their orbits can be circularized by aerodynamic gas drag. We find that the dynamical implantation of CI asteroids from ∼15–25 au is very efficient with ∼5% of ∼100-km planetesimals reaching stable orbits in the asteroid belt by the end of the protoplanetary gas disk lifetime. The efficiency is reduced when planetesimal ablation is accounted for. The implanted population subsequently evolved by collisions and was depleted by dynamical instabilities. The model can explain why CIs are isotopically distinct from other C-type asteroids which presumably formed at ∼5–10 au.

^1,2Rachel A. Slank,¹Vincent F. Chevrier
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115914]
¹Arkansas Center for Space and Planetary Sciences, University of Arkansas, 346 Arkansas Ave, Fayetteville, AR 72701, USA
²Lunar and Planetary Institute, Universities Space Research Association, 3600 Bay Area Blvd., Houston, TX 77058, USA
Copyright Elsevier

The definition of habitability on Mars is intimately linked to the stability of liquid water on the surface or near sub-surface. Brines provide the best pathway to stabilize liquid water, and form through deliquescence where a solid salt crystal transitions into an aqueous solution when exposed to a humid atmosphere. In a typical brine controlled by temperature and water relative humidity, ternary mixtures represent the best potential liquid brines. Here we modeled the deliquescence relative humidity (DRH) and the eutonic relative humidity (RH) of ternary salt mixtures. Chloride, chlorate, and perchlorate were modeled with either calcium or magnesium as the cation at temperatures ranging from 223 to 273 K. For the calcium ternary mixtures, the main salt composition precipitating at the DRH was dominated by calcium chloride, and by magnesium perchlorate in the magnesium ternary system. The hydration state of the precipitating salts systematically increased as temperature decreased. The eutonic RH for the calcium mixtures ranged from 14.24% at 273 K and increased to 43.54% by the coldest temperature of 223 K. The eutonic RH for the magnesium mixtures was significantly higher than the calcium counterpart, at 49.76% at 273 K and increased to 53.09% by 223 K. Calcium perchlorate was the predominate eutonic precipitate for the calcium mixtures, and magnesium chlorate for the magnesium mixtures., This study shows that ternary mixtures bring a slight improvement to the stability of brines on Mars compared to single salts or binary mixtures.

¹Zachary A. Torrano et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14109]
¹Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC, USA
Published by arrangement with John Wiley & Sons

We report Nd and Sm isotopic compositions of four samples of Ryugu returned by the Hayabusa2 mission, including “A” (first touchdown) and “C” (second touchdown) samples, and several carbonaceous chondrites to evaluate potential genetic relationships between Ryugu and known chondrite groups and track the cosmic ray exposure history of Ryugu. We resolved Nd and Sm isotopic anomalies in small (<20 ng Nd and Sm) sample sizes via thermal ionization mass spectrometer using 1013 Ω amplifiers. Ryugu samples exhibit resolvable negative μ142Nd values consistent with carbonaceous chondrite values, suggesting that Ryugu is related to the parent bodies of carbonaceous chondrites. Ryugu’s negative μ149Sm values are the result of exposure to galactic cosmic rays, as demonstrated by the correlation between 150Sm/152Sm and 149Sm/152Sm ratios that fall along the expected neutron capture correlation line. The neutron fluence calculated in the “A” samples (2.75 ± 1.94 × 1015 n cm−2) is slightly higher compared to the “C” samples (0.95 ± 2.04 × 1015 n cm−2), though overlapping within measurement uncertainty. The Sm results for Ryugu, at this level of precision, thus are consistent with a well-mixed surface layer at least to the depths from which the “A” and “C” samples derive.

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.