¹Christopher J. Cline II,²Mark J. Cintala
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13886]
¹Jacobs Technology, NASA Johnson Space Center, Astromaterials Research and Exploration Science, Mail Code X13, 2101 NASA Parkway, Houston, Texas, 77058 USA
²NASA Johnson Space Center, Astromaterials Research and Exploration Science, Mail Code X13, 2101 NASA Parkway, Houston, Texas, 77058 USA
Published by arrangement with John Wiley & Sons

The dimensions of relatively small-scale impact craters are undoubtedly sensitive to the physical properties of the target. Studying gravity-controlled crater formation at the laboratory scale often relies on cohesionless, granular materials, which, by their nature, make it difficult to separate the individual contributions to this process from all of the relevant target properties. Here, we conduct a suite of impact experiments to isolate and evaluate the effects of density, porosity, and internal friction on impact crater morphometry. Each made from one of four different granular materials, targets were impacted vertically with 4.76 mm aluminum projectiles at an average speed of ~1.55 km s−1. Two different methods were used to load these materials into the target bucket (pouring and sieving), resulting in targets that varied in bulk density and internal friction. The experimental results indicate that depth–diameter ratios of the craters are largely influenced by the loading method of the target material and are sensitive to the friction and porosity of the targets. Sieved targets (relatively higher density, lower porosity, and higher friction angle) produce craters that are markedly shallower, have notably smaller volumes, and exhibit a flat-floored morphology, with some possessing small central mounds. Flat-floored craters are typically attributed to a strength-layered target; in these experiments, however, they were produced in cohesionless targets. This study demonstrates that a flat floor is not necessarily diagnostic of strength layering in a target and, in some instances, might be the consequence of greater shear strengths in granular materials with high coefficients of static friction.

Marion Auxerre, François Faure, and Delphine Lequin
Meteoritics & Plaentary Science (in Press)
Link to Article [https://doi.org/10.1111/maps.13830]
CNRS, CRPG, UMR 7358, 15 rue Notre Dame des Pauvres F-54501 Vandoeuvre-lès-Nancy France
Published by arrangement with John Wiley & Sons

Chondrules, the major constituent of chondrites, are millimeter-sized igneous objects resulting from the crystallization of silicate liquids produced by the partial or complete melting of chondritic precursors, whose exact nature remains disputed. Various chondrule textures are observed as a function of the extent of the initial melting event. Here, we report dynamic crystallization experiments performed with a broad range of cooling rates (2–750 °C h⁻¹) from superliquidus or subliquidus initial conditions to demonstrate the control of nucleation on the final chondrule texture. Classical crypto-porphyritic, micro-porphyritic, and porphyritic olivine textures were reproduced in subliquidus experiments in which heterogeneous nucleation dominates. In contrast, we were unable to reproduce barred olivine textures, regardless of the cooling rates investigated from superliquidus conditions; instead, macro-porphyritic textures were systematically obtained at low cooling rates (<10 °C h⁻¹). The small number and large size of crystals in the macro-porphyritic texture are consistent with the initial step of superheating and the presence of long embayments that indicate an initial episode of rapid growth due to delayed nucleation. Crystals then acquired polyhedral shapes during a subsequent episode of slow growth. When the growth rate is too slow to decrease the degree of supersaturation in the liquid, a new episode of rapid growth produces a new generation of melt inclusions.

David J. Lawrence¹, Patrick N. Peplowski¹, Jack T. Wilson¹, and Richard C. Elphic²
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2022JE007197]
¹Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland
²NASA Ames Spaceflight Center, Moffett Field, California
Published by arrangement with John Wiley & Sons

A global map of bulk hydrogen abundances on the Moon is presented. This map was generated using data from the Lunar Prospector Neutron Spectrometer. This map required corrections for variations due to rare-earth elements, and was calibrated to Apollo sample hydrogen abundances. Since neutron-derived measurements sample hydrogen content to a depth of tens of cm, these results provide complementary insights to those provided by studies using spectral reflectance data, which sample depths of order μm. Comparison of these abundances to Apollo sample values suggest that the samples reflect actual hydrogen content on the lunar surface, not dominantly from non-lunar contamination. The average lunar hydrogen abundance is 47 ppm with a systematic uncertainty of ∼10 ppm. This is consistent with bulk hydrogen from solar wind emplacement. A bulk hydrogen enhancement (50–68 ppm) has been identified at the Moon’s largest pyroclastic deposit (Aristarchus Plateau), which corroborates prior observations that hydrogen and/or water plays a role in lunar magmatic events. Global data show a correlation between hydrogen and evolved materials rich in incompatible trace elements (i.e., KREEP type rocks), with a hydrogen excess of 14–36 ppm in these materials. Based on this hydrogen enhancement, we estimate a lower-limit water abundance within urKREEP materials (i.e., the final ∼2% of the lunar magma ocean) of 320–820 ppm H₂O. This observation implies that water played a role in the original magma-ocean formation and solidification with a lower-limit water content in the original lunar magma ocean of 7–16 ppm or higher.

Paolo A. Sossi¹, Anat Shahar²
Elements – Link to Article [https://doi.org/10.2138/gselements.17.6.407]
¹ETH Zürich, Institute of Geochemistry and Petrology, Zürich, CH-8092, Switzerland
²Carnegie Institution for Science, Earth and Planets Laboratory, Washington, DC, 20015-1305, USA
Copyright Elsevier

Evaporation of magma oceans exposed to space may have played a role in the chemical and isotopic compositions of rocky planets in our Solar System (e.g., Earth, Moon, Mars) and their protoplanetary antecedents. Chemical depletion of moderately volatile elements and the enrichment of these elements’ heavier isotopes in the Moon and Vesta relative to chondrites are clear examples. Evaporation is also thought to be an important process in some exoplanetary systems. Identification of evaporation signatures among the rock-forming elements could elucidate important reactions between melts and vapors during planet formation in general, but the process is more complicated than is often assumed.

Haolan Tang, Edward D. Young
Elements – Link to Article [https://doi.org/10.2138/gselements.17.6.401]
University of California, Los Angeles Department of Earth, Planetary, and Space Sciences, 595 Charles E. Young Dr. East, Los Angeles, CA, 90095, USA
Copyright Elsevier

Evaporation of magma oceans exposed to space may have played a role in the chemical and isotopic compositions of rocky planets in our Solar System (e.g., Earth, Moon, Mars) and their protoplanetary antecedents. Chemical depletion of moderately volatile elements and the enrichment of these elements’ heavier isotopes in the Moon and Vesta relative to chondrites are clear examples. Evaporation is also thought to be an important process in some exoplanetary systems. Identification of evaporation signatures among the rock-forming elements could elucidate important reactions between melts and vapors during planet formation in general, but the process is more complicated than is often assumed.

Christoph Burkhardt
Elements – Link to Article [https://doi.org/10.2138/gselements.17.6.395]
University of Münster, Institut für Planetologie, Wilhelm-Klemm-Straße 10, D-48149 Münster, Germany
Copyright Elsevier

The detection of exoplanets and accretion disks around newborn stars has spawned new ideas and models of how our Solar System formed and evolved. Meteorites as probes of geologic deep time can provide ground truth to these models. In particular, stable isotope anomalies in meteorites have recently emerged as key tracers of material flow in the early Solar System, allowing cosmochemists to establish a “planetary isotopic genealogy”. Although not complete, this concept has substantially advanced our understanding of Solar System evolution, from the collapse of the Sun’s parental molecular cloud to the accretion of the planets.

Marianna Marchini¹, Massimo Gandolfi¹, Lucia Maini¹, Lucia Raggetti², and Matteo Martelli²
Proceedings of the National Academy of Science of the USA (PNAS) 119 (14) e2119194119 Link to Article [https://doi.org/10.1073/pnas.2123171119]
¹Department of Chemistry “Giacomo Ciamician”, University of Bologna, 40126, Bologna, Italy
²Department of Philosophy and Communication Studies, University of Bologna, 40126, Bologna, Italy

Sulfate aerosols have long been implicated as a primary forcing agent of climate change and mass extinction in the aftermath of the end-Cretaceous Chicxulub bolide impact. However, uncertainty remains regarding the quantity, residence time, and degree to which impact-derived sulfur transited the This paper explores the chemistry of mercury as described in ancient alchemical literature. Alchemy’s focus on the knowledge and manipulation of natural substances is not so different from modern chemistry’s purposes. The great divide between the two is marked by the way of conceptualizing and recording their practices. Our interdisciplinary research group, composed of chemists and historians of science, has set off to explore the cold and hot extraction of mercury from cinnabar. The ancient written records have been perused in order to devise laboratory experiments that could shed light on the material reality behind the alchemical narratives and interpret textual details in a unique perspective. In this way, it became possible to translate the technical lore of ancient alchemy into the modern language of chemistry. Thanks to the replication of alchemical practices, chemistry can regain its centuries-long history that has fallen into oblivion.

S. N. Ferguson, A. R. Rhoden, M. R. Kirchoff
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2022JE007204]
Soutwest Research Institute Boulder, CO, USA
Published by arrangement with John Wiley & Sons

Recent dynamical modeling of the formation and evolution of the Saturnian satellites suggests that the ages of the mid-sized inner moons (Mimas, Enceladus, Tethys, Dione, and Rhea) could be as young as 100 Myr. This estimate is in contrast to most previous modeling and observational work that suggest an age more contemporaneous with the formation of Saturn 4.5 Ga ago. Given the heritage of using craters to constrain surface ages, we examine the impact craters of Dione using imagery from NASA’s Cassini ISS camera and analyze their size-frequency distributions (SFDs) to understand impactor populations. We survey four areas across different geologic terrains and compare our crater counts to standard outer solar system production functions. In addition to crater counts, we study several crater types such as elliptical and polygonal to further examine the bombardment source for the craters. We find evidence for a Saturn-specific planetocentric impactor source, as none of the standard production functions fit the data. We compare our Dione data with our work on Tethys and find similarly shaped SFDs between the satellites. However, Dione’s surface has been extensively modified to remove smaller craters (D ∼< 5km) and has been bombarded by larger impactors, creating more D ∼> 20 km on Dione than Tethys. In contrast, Tethys more generally represents an ancient unmodified surface within the Saturn system. More complete observations and assessment of the cratering records on the satellites of Uranus and Neptune’s moon Triton would enable better constraints on the bombardment history of the Saturn system.

Cauê S. Borlina¹, Benjamin P. Weiss¹, James F. J. Bryson³, Philip J. Armitage^3,4
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2021JE007139]
¹Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
²Department of Earth Sciences, Oxford University, Oxford, UK
³Center for Computational Astrophysics, Flatiron Institute, 162 Fifth Avenue, New York, NY,USA
⁴Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY, USA
Published by arrangement with John Wiley & Sons

The evolution and lifetime of protoplanetary disks (PPDs) play a central role in the formation and architecture of planetary systems. Astronomical observations suggest that PPDs evolve in two timescales, accreting onto the star for up to several million years (Myr) followed by gas-dissipation within ≲1 Myr. Because solar nebula magnetic fields are sustained by the gas of the protoplanetary disk, we can use paleomagnetic measurements to infer the lifetime of the solar nebula. Here we use paleomagnetic measurements of meteorites to constrain this lifetime and investigate whether the solar nebula had a two-timescale evolution. We report on paleomagnetic measurements of bulk subsamples of two CO carbonaceous chondrites: Allan Hills A77307 and Dominion Range 08006. If magnetite in these meteorites can acquire a crystallization remanent magnetization that recorded the ambient field during aqueous alteration, our measurements suggest that the local magnetic field strength at the CO parent-body location was <0.9 µT at some time between 2.7-5.1 Myr after the formation of calcium-aluminum-rich inclusions. Coupled with previous paleomagnetic studies, we conclude that the dissipation of the solar nebula in the 3-7 AU region occurred <1.5 Myr after the dissipation of the nebula in the 1-3 AU region, suggesting that protoplanetary disks go through a two-timescale evolution in their lifetime consistent with dissipation by photoevaporation and/or magnetohydrodynamic winds. We also discuss future directions necessary to obtain robust records of solar nebula fields using bulk chondrites, including obtaining ages from meteorites and experimental work to determine how magnetite acquires magnetization during chondrite parent-body alteration.

Saverio Cambioni¹, Katherine de Kleer², Michael Shepard³
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2021JE007091]
¹Department of Planetology, Kobe University, Kobe, Department of Earth, Atmospheric & Planetary Sciences, Massachusetts Institute of Technology, 3Cambridge, MA, USA
²Division of Geological & Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
³Department of Environmental, Geographical & Geological Sciences, Bloomsburg University, Bloomsburg, PA, USA
Published by arrangement with John Wiley & Sons

Main-belt asteroid (16) Psyche is the largest M-type asteroid, a class of object classically thought to be the metal cores of differentiated planetesimals and the parent bodies of the iron meteorites. de Kleer, Cambioni, and Shepard (2021) presented new data from the Atacama Large Millimiter Array (ALMA), from which they derived a global best-fit thermal inertia and dielectric constant for Psyche, proxies for regolith particle size, porosity, and/or metal content, and observed thermal anomalies that could not be explained by surface albedo variations only. Motivated by this, here we fit a model to the same ALMA dataset that allows dielectric constant and thermal inertia to vary across the surface. We find that Psyche has a heterogeneous surface in both dielectric constant and thermal inertia but, intriguingly, we do not observe a direct correlation between these two properties over the surface. We explain the heterogeneity in dielectric constant as being due to variations in the relative abundance of metal and silicates. Furthermore, we observe that the lowlands of a large depression in Psyche’s shape have distinctly lower thermal inertia than the surrounding highlands. We propose that the latter could be explained by a thin mantle of fine regolith, fractured bedrock, and/or implanted silicate-rich materials covering an otherwise metal-rich surface. All these scenarios are indicative of a collisionally evolved world.