^1,2Jan L. Hellmann,^1,3Jonas M. Schneider,^1,3Elias Wölfer,³Joanna Drążkowska,¹Christian A. Jansen,^1,3Timo Hopp,^1,3Christoph Burkhardt,^1,3Thorsten Kleine
The Astrophysical Journal 946, L34 Open Access Link to Article [DOI 10.3847/2041-8213/acc102]
¹Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, D-48149 Münster, Germany;
²Department of Geology, University of Maryland, 8000 Regents Drive, College Park, MD 20742, USA
³Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, D-37077 Göttingen, Germany

Carbonaceous chondrites are some of the most primitive meteorites and derive from planetesimals that formed a few million years after the beginning of the solar system. Here, using new and previously published Cr, Ti, and Te isotopic data, we show that carbonaceous chondrites exhibit correlated isotopic variations that can be accounted for by mixing among three major constituents having distinct isotopic compositions, namely refractory inclusions, chondrules, and CI chondrite-like matrix. The abundances of refractory inclusions and chondrules are coupled and systematically decrease with increasing amount of matrix. We propose that these correlated abundance variations reflect trapping of chondrule precursors, including refractory inclusions, in a pressure maximum in the disk, which is likely related to the water ice line and the ultimate formation location of Jupiter. The variable abundance of refractory inclusions/chondrules relative to matrix is the result of their distinct aerodynamical properties resulting in differential delivery rates and their preferential incorporation into chondrite parent bodies during the streaming instability, consistent with the early formation of matrix-poor and the later accretion of matrix-rich carbonaceous chondrites. Our results suggest that chondrules formed locally from isotopically heterogeneous dust aggregates, which themselves derive from a wide area of the disk, implying that dust enrichment in a pressure trap was an important step to facilitate the accretion of carbonaceous chondrite parent bodies or, more generally, planetesimals in the outer solar system.

¹Ryan C. Ogliore
Geochemistry (Chemie der Erde) (in Press) Link to Article [https://doi.org/10.1016/j.chemer.2023.126046]
¹McDonnell Center for the Space Sciences, Washington University in St. Louis, 1 Brookings Dr., St. Louis 63130, MO, USA
Copyright Elsevier

NASA’s Stardust mission returned rocky material from the coma of comet 81P/Wild 2 (pronounced “Vilt 2”) to Earth for laboratory study on January 15, 2006. Comet Wild 2 contains volatile ices and likely accreted beyond the orbit of Neptune. It was expected that the Wild 2 samples would contain abundant primordial molecular cloud material—interstellar and circumstellar grains. Instead, the interstellar component of Wild 2 was found to be very minor, and nearly all of the returned particles formed in broad and diverse regions of the solar nebula. While some characteristics of the Wild 2 material are similar to primitive chondrites, its compositional diversity testifies to a very different origin and evolution history than asteroids. Comet Wild 2 does not exist on a continuum with known asteroids. Collisional debris from asteroids is mostly absent in Wild 2, and it likely accreted dust from the outer and inner Solar System (across the putative gap created by a forming Jupiter) before dispersal of the solar nebula. Comets are a diverse set of bodies, and Wild 2 may represent a type of comet that accreted a high fraction of dust processed in the young Solar System.

^1,2Christian J. Renggli,³Aleksandra N. Stojic,³Andreas Morlok,¹Jasper Berndt,³Iris Weber,¹Stephan Klemme,³Harald Hiesinger
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2023JE007895]
¹Institut für Mineralogie, Universität Münster, Münster, Deutschland
²Max Planck Institut für Sonnensystemforschung, Göttingen, Deutschland
³Institut für Planetologie, Universität Münster, Münster, Deutschland
Published by arrangement with John Wiley & Sons

We propose that the observed enrichment of sulfur at the surface of Mercury (up to 4 wt.%) is the product of silicate sulfidation reactions with a S-rich reduced volcanogenic gas phase. Here, we present new experiments on the sulfidation behavior of olivine, diopside, and anorthite. We investigate these reaction products, and those of sulfidized glasses with Mercury compositions previously reported, by mid-IR reflectance spectroscopy. We investigate both the reacted bulk materials as powders as well as cross-sections of the reaction products by in situ micro-IR spectroscopy. The mid-IR spectra confirm the presence of predicted reaction products including quartz. The mid-IR reflectance of sulfide reaction products, such as CaS (oldhamite) or MgS (niningerite), is insufficient to be observed in the complex run products. However, the ESA/JAXA BepiColombo mission to Mercury will be able to test our hypothesis by investigating the correlated abundances of sulfides with other reaction products such as quartz.

¹Jiawei Zhao et al. (>10)
Earth and Planetary Science Letters 626, 118507 Link to Article [https://doi.org/10.1016/j.epsl.2023.118507]
¹State Key Laboratory of Geological Processes and Mineral Resources, Planetary Science Institute, School of Earth Sciences, China University of Geosciences, Wuhan, 430074, China
²Space Science and Technology Centre, The Institute for Geoscience Research, School of Earth and Planetary Science, Curtin University, GPO Box U1987, Perth, WA 6845, Australia
Copyright Elsevier

Zircon with granular texture from hypervelocity impact structures can be used to estimate the thermodynamic conditions of impact processes, including pressure and temperature, and in some cases the timing of impact events via U-Pb geochronology. However, two disparate formation models have been proposed to explain the occurrence of zircon neoblasts that preserve systematic orientation relations; one involves zircon-reidite phase transformations (FRIGN zircon), whereas the other features melting and thermal dissociation of zircon in the absence of reidite. Distinguishing between these models is hampered by the lack of observational constraints on the intermediate transformation steps at nanoscale, and what processes give rise to observed systematic orientation relations among zircon neoblasts. Here we report new analyses of reidite-bearing and granular zircons from peak ring core samples of the Chicxulub impact structure using nanoscale methods. We describe lamellar and lense-like reidite habits associated with reidite twins in shocked zircon from impact melt-bearing breccia, along with the first observation of nanoscale zircon granules forming locally within preserved reidite lamellae. The crystallographic orientation of the zircon nano-granules matches the orientations predicted by the FRIGN zircon model, confirming they formed directly by solid-state reversion of reidite to zircon, and represent the earliest stages of the formation of granular zircon. Minor occurrences of baddeleyite at the interface of reidite and neoblastic zircon domains suggest that the reversion of reidite to zircon can occur together with local ZrSiO4 dissociation driven either by the loss of SiO2, which creates excess zirconia, or by local thermal dissociation of reidite. Other partially- and fully-granular zircon grains from the same impact melt-bearing breccia also preserve systematic orientation relationships among zircon neoblasts, consistent with having transformed directly from reidite. The observation that zircon neoblasts maintain systematic orientations from nanoscale to microscale in granular zircon supports the idea that neoblast orientations are encoded at the nucleation stage via solid state phase transformation. Observations in this study provide direct evidence to explain the nature of systematic high-pressure phase transitions involving zircon and have implications for unraveling the pressure-temperature history of zircon phase transitions in large impacts on Earth or other planetary bodies.

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.