¹Libby D. Tunney,¹Patrick J. A. Hill,¹Christopher D. K. Herd,^1,2Robert W. Hilts,¹Miranda C. Holt
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13803]
¹Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3 Canada
²Department of Physical Sciences, MacEwan University, Edmonton, Alberta, T6J 4S2 Canada
Published by arrangement with John Wiley & Sons

Soluble organic matter analyses of astromaterials can provide valuable information on the chemistry of our solar system and the processes that occur within it. The surface of the Earth, however, is a significant source of organic compounds due to the presence of life; this environment represents a major source of potential contamination for recently fallen meteorites. Here, we analyze select stones of the CM2 Aguas Zarcas carbonaceous chondrite, which fell on April 23, 2019, in Aguas Zarcas, San Carlos county, Alajuela province, Costa Rica, with the goal of determining the complement of intrinsic and contaminant soluble organic matter. The specimens were collected pre- and post-rainfall, days to weeks after the stones fell on the Earth. Through gas chromatography-mass spectrometry analysis of soluble organic matter in dichloromethane and hot water extracts of meteorite powders, we differentiate between extraterrestrial and contaminant sources for each organic compound detected. In this study, N-tert-butyldimethylsilyl- N-methyltrifluoroacetamide (MTBSTFA) was used to derivatize the hot water extracts to test out its “one-pot” extraction capabilities. The majority of the detectable organic compounds are contaminants and can be explained as being sourced from the terrestrial surface onto which the meteorite fell. Our results have implications for how environmental factors, such as land use and rainfall events in this case, can impact the intrinsic organics in carbonaceous chondrites.

¹Randy G. Hopkins,¹John G. Spray
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13799]
¹Planetary and Space Science Centre, University of New Brunswick, 2 Bailey Drive, Fredericton, New Brunswick, E3B 5A3 Canada
Published by arrangement with John Wiley & Sons

Numerical computing software (via MathWorks MATLAB) has been developed to understand the relationship between shock wave passage in geological targets (i.e., heterogeneous media) and the formation of shock veins and associated high-pressure/temperature polymorphs. This approach takes into consideration the pressure due to the passage of the shock front, subsequent rarefaction unloading pressures, and associated heating and cooling rates. The model is applied to calculate pressure–temperature–time conditions for coesite- and stishovite-bearing shock veins within metaquartzites of the Vredefort impact structure of South Africa. To constrain the model, the position of the host metaquartzites at the time of impact is first reconstructed. The developed code then passes the appropriate shock conditions through the target to re-create the shock wave, while simultaneously forming and cooling the shock veins via 2-D steady-state conduction. We have found that (1) at the time of shock vein formation (2.4 s following the initial contact of the projectile), the shock front pressure was 13.8 GPa and the width of the shock wave was of 27 km; (2) the melt within the shock veins initially reached ~3000 °C, which corresponds to the melting temperature of the target rock at 13.8 GPa. Simulation results indicate that conditions reach the stishovite stability field within 2 ms of vein formation (~10–14 GPa; 2000–3000 °C), followed by coesite within 1.29 s (~3–10 GPa; 600–2000 °C). The dwell time of the modeled shock vein system is 4.35 s. The shock vein system is completely solidified 33.4 s after the initial shock front passage. The calculated P–T–t path of the model indicates that the polymorphs within the shock veins of the metaquartzites at Vredefort formed under their normal stability field conditions following rarefaction wave decompression.

^1,2Quinn R.Shollenberger,²Jan Render¹Michelle K.Jordan,¹Kaitlyn A.McCain,²Samuel Ebert,²Addi Bischoff,²Thorsten Kleine,¹Edward D.Young
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.03.001]
¹Department of Earth, Planetary, and Space Sciences, University of California Los Angeles, 595 Charles E Young Dr E, Los Angeles, CA 90095, USA
²Institut für Planetologie, University of Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany
Copyright Elsevier

Calcium-aluminum-rich inclusions (CAIs) are highly refractory objects found in different chondrite groups and represent some of the oldest known solids of the Solar System. As such, CAIs provide key information regarding the conditions prevailing in the solar protoplanetary disk as well as subsequent mixing and transport processes. Many studies have investigated CAIs for their isotopic compositions and reported nucleosynthetic isotope anomalies in numerous elements, which are typically explained by the variable incorporation of isotopically highly anomalous presolar phases. However, with the exception of 54Cr-enriched nanospinels, the exact presolar phases responsible for the isotopic heterogeneities are yet to be identified. To address this issue, we here present in-situ Ti isotopic analyses obtained on a diverse set of CAIs from various CV3 chondrites. The in-situ measurements were performed by targeting individual mineral phases of 15 CAIs with laser-ablation mass spectrometry and indicate significant inter- and intra-CAI isotopic heterogeneity in the neutron-rich isotope 50Ti. This is particularly pronounced for primitive fine-grained CAIs, whereas coarse-grained CAIs, which have been subject to melting, exhibit smaller degrees of Ti isotopic heterogeneity.

To further investigate this Ti isotopic heterogeneity, we additionally obtained Ti isotopic compositions of sequential acid leachates from two fine-grained and two coarse-grained CAIs derived from CV3 chondrites. In contrast to potential expectations from the first part of the study, we do not observe any significant intra-CAI Ti isotopic heterogeneity between the different leaching steps. The lack of intra-CAI Ti isotopic heterogeneity in the acid leachate samples of this study likely reflects that the leaching procedure is unable to efficiently separate the carriers of isotopically anomalous Ti in CAIs. By comparing the bulk CAI Ti isotope compositions with Ti isotope data for hibonite-rich objects from the literature, we find that the range of Ti isotope compositions recorded by CAIs from various chondrite groups can be accounted for by the averaging of hibonite grains. In turn, the variable Ti isotope compositions of hibonite grains can be explained by the averaging of isotopically diverse presolar grains present in the Sun’s parental molecular cloud. This effect of averaging is statistically supported by the central limit theorem, and the concept has the potential to be useful for other isotopic systems.

¹Thomas S.Kruijer,²Christoph Burkhardt,¹Lars E.Borg,^2,3Thorsten Kleine
Eaerth and Planetary Science Letters 584, 117440 Link to Article [https://doi.org/10.1016/j.epsl.2022.117440]
¹Nuclear and Chemical Sciences Division, Lawrence Livermore National Laboratory, 7000 East Avenue (L-231), Livermore, CA 94550, USA
²Institut für Planetologie, University of Münster, Wilhelm-Klemm-Strasse 10, 48149, Münster, Germany
³Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
Copyright Elsevier

The origin of pallasites—stony-iron meteorites mainly composed of olivine and Fe-Ni metal—is debated and proposed formation scenarios broadly range from models that explain pallasite formation by internal processes in the mantle of a differentiated planetesimal to those that involve impact–induced mixing of core and mantle materials. Here, the origin of pallasites is examined by studying the nebular source regions of their precursor material using Mo isotopes and their history of metal-silicate segregation using Hf-W chronometry. We report new Mo and W isotopic data for a large suite of pallasite metal samples, alongside Pt isotope data to quantify superimposed cosmic ray exposure effects. Most main-group pallasites exhibit uniform pre-exposure 182W and Mo isotopic compositions that bear an excellent similarity to those of IIIAB iron meteorites. Four main-group pallasites and the IIIAB iron Thunda have more radiogenic pre-exposure 182W compositions, but display the same Mo isotopic composition as other main-group pallasites and IIIAB irons. This strong chronological and genetic link strongly suggests that main-group pallasite metal originated in the IIIAB parent body core. This, combined with prior Pd-Ag chronometric evidence for an early collisional disruption of the IIIAB parent body, implies that main-group pallasites formed by impact–induced mixing of metal and silicates rather than by an internal process on the IIIAB parent body. This mixing led to elevated 182W compositions in some pallasites, which are best accounted for by partial re-equilibration of IIIAB metal with radiogenic 182W from the colliding body. Collectively, our results support models that explain main-group pallasite formation by injection of pallasite metal into the mantle of another differentiated body, implying that pallasite silicates did not primarily derive from the IIIAB mantle, but instead from that of the colliding body.

¹Ariel N.Deutsch,²Joseph S.Levy,^1,3James L.Dickson,¹James W.Head
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.114990]
¹Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, USA
²Department of Geology, Colgate University, Hamilton, NY 13346, USA
³Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
Copyright Elsevier

Soil salt deliquescence and soil porewater solution growth are key processes that generate potentially habitable conditions in hyperarid environments on Earth and could form near-surface pore waters on Mars. However, direct detection of soils darkened by saline porewater solutions on Mars has proven difficult owing to the limited number of imaging opportunities over potential brine-bearing sites, the limited diel temporal coverage of orbital sensors, and the diversity of spectroscopic properties of potentially brine-bearing substrates that limits direct detection of hydrated mineral phases. Here, we explore how these observational limitations would affect the interpretation of highly dynamic soil salt patches observed in the McMurdo Dry Valleys, Antarctica. These salt patches show daily and seasonal albedo change, darkening and brightening over timescales of minutes. Fully darkened conditions occur at a median surface relative humidity of 67.9 ± 10.7%, while bright conditions occur at lower median surface relative humidity of 38.9 ± 14.5%, leading to the interpretation that the albedo changes are caused by soil salt deliquescence and brine droplet growth. These humidity thresholds and the daily hysteresis between deliquesced and effloresced conditions are consistent with the properties of sulfate and chloride salts found at the site, but occur on timescales much faster than those observed under laboratory conditions (minutes vs. hours–days). Darkened soil patch conditions are most common between 21:00 and 06:00 local time, and are not detected during 78% of afternoon imaging opportunities, suggesting that episodic, afternoon satellite imaging would not be effective in resolving rapid albedo changes on similar planetary landscapes such as Mars. Instead, synoptic, high-cadence imaging is a more suitable remote sensing tool for evaluating albedo changes driven by surface salt deliquescence and efflorescence.

Francesca E.DeMeo et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.114971]
¹Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
Copyright Elsevier

In this work we identify spectral similarities between asteroids and meteorites. Using spectral features such as absorption bands and spectral curvature, we identify spectral matches between 500 asteroid spectra and over 1,000 samples of RELAB meteorite spectra over visible plus near-infrared wavelengths (0.45–). We reproduce and confirm many major and previously known meteorite-asteroid connections and find possible new, more rare or less-established connections. Well-established connections include: ordinary chondrites with S-complex asteroids; pristine CM carbonaceous chondrites with Ch-type asteroids and heated CMs with C-type asteroids ; HED meteorites with V-types; enstatite chondrites with Xc-type asteroids; CV meteorites with K-type asteroids; Brachinites, Pallasites and R chondrites with olivine-dominated A-type asteroids.

In addition to the link between ordinary chondrite meteorites with S-complex asteroids, we find a trend from Q, Sq, S, Sr to Sv correlates with LL to H, with Q-types matching predominately to L and LL ordinary chondrites, and Sr and Sv matching predominantly with L and H ordinary chondrites. We find ordinary chondrite samples that match to the X-complex. These are measurements of slabs and many are labeled as dark or black (shocked) ordinary chondrites. We find carbonaceous chondrite samples having spectral slopes large enough to match D-type asteroid spectra.

We find in many cases the asteroid type to meteorite type links are not unique, for classes with and without distinct spectral features. While there are examples of dominant matches between an asteroid class and meteorite class that are well established, there are less common but still spectrally compatible matches between many asteroid types and meteorite types. This result emphasizes the diversity of asteroid and meteorite compositions and highlights the degeneracy of classification by spectral features alone requiring additional measurements to firmly establish asteroid-meteorite links. Recent and upcoming spacecraft missions will shed light on the compositions of many of the asteroid classes, particularly those without diagnostic features, (C-, B-, X-, and D-types), with measurements of C-type Ceres, C-type Ryugu, B-type Bennu, M-type Psyche, and C-, P-, and D-types as part of the Lucy mission.

^1,2Erbin Shi,²Alian Wang,³Huafang Li,²Ryan Ogliore,¹Zongcheng Lin
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2021JE007108]
¹School of Space Science and Physics, Shandong Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, Shandong, 264209 China
²Department of Earth & Planetary Sciences and McDonnell Center for the Space Sciences Washington University in St. Louis, MO, 63130 USA
³The Institute of Materials Science & Engineering, Washington University in St. Louis, MO, 63130 USA
Published by arrangement with John Wiley & Sons

Ordinary γ-CaSO₄ is a metastable calcium sulfate, while γ-CaSO₄ from the hyperarid region on Earth and from Mars has been found with abnormally high stability. In this study, we used multiple microanalyses to characterize the chemical and structural properties of two such γ-CaSO₄: one from Atacama soil (#10-d30) and the other from Martian meteorite MIL03346,168. Silicon was determined to be quasi-homogeneously distributed in Atacama γ-CaSO₄, while both silicon and phosphorus were detected in Martian γ-CaSO₄. We found the abnormally high stability of those γ-CaSO₄ from hyperarid environments was due to the chemical impurities which filled their structural tunnels and blocked the entrance of atmospheric H₂O, with non-detectable structural distortion. We propose that the γ-CaSO₄ with Si or Si and P impurities could have igneous origin or evaporative origin. Due to the extreme similarity in the structures of bassanite and γ-CaSO₄, their XRD patterns are almost non-distinguishable; thus some martian “bassanite” minerals identified by Curiosity’s CheMin instrument at Gale crater can actually be γ-CaSO₄. The structural tunnels in γ-CaSO₄ would allow ions and ionic groups to fill, thus providing meaningful insights about the geological and geochemical processes experienced by it during the formation and transformation. The Raman spectrometer carried by the Perseverance and by ExoMars rovers will help the selection of samples enriched in γ-CaSO₄ at Jezero Crater and Oxia Planum, which should be sampled for in-depth analysis on Mars and back to Earth.

¹Erwin Dehouck et al. (>10)
Journal of Geophysical Research, Planets (in Press) Open Access Link to Article [https://doi.org/10.1029/2021JE007103]
¹Univ Lyon, UCBL, ENSL, UJM, CNRS, LGL-TPE, F, 69622 Villeurbanne, France
Published by arrangement with John Wiley & Sons

Glen Torridon is a topographic trough located on the slope of Aeolis Mons, Gale crater, Mars. It corresponds to what was previously referred to as the “clay-bearing unit”, due to the relatively strong spectral signatures of clay minerals (mainly ferric smectites) detected from orbit. Starting in January 2019, the Curiosity rover explored Glen Torridon for more than 700 sols (Martian days). The objectives of this campaign included acquiring a detailed understanding of the geologic context in which the clay minerals were formed, and determining the intensity of aqueous alteration experienced by the sediments. Here, we present the major-element geochemistry of the bedrock as analyzed by the ChemCam instrument. Our results reveal that the two main types of bedrock exposures identified in the lower part of Glen Torridon are associated with distinct chemical compositions (K-rich and Mg-rich), for which we are able to propose mineralogical interpretations. Moreover, the topmost stratigraphic member exposed in the region displays a stronger diagenetic overprint, especially at two locations close to the unconformable contact with the overlying Stimson formation, where the bedrock composition significantly deviates from the rest of Glen Torridon. Overall, the values of the Chemical Index of Alteration determined with ChemCam are elevated by Martian standards, suggesting the formation of clay minerals through open-system weathering. However, there is no indication that the alteration was stronger than in some terrains previously visited by Curiosity, which in turn implies that the enhanced orbital signatures are mostly controlled by non-compositional factors.

¹Eric T. Parker,²Queenie H. S. Chan,³Daniel P. Glavin,⁴Jason P. Dworkin
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13794]
¹Astrobiology Analytical Laboratory, Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland, 20771 USA
²Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey, TW20 0EX UK
³School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA UK
Published by arrangement with John Wiley & Sons

Amino acid abundances in acid-hydrolyzed hot water extracts of gold foils containing five Category 3 (carbon-rich) Hayabusa particles were studied using liquid chromatography with tandem fluorescence and accurate mass detection. Initial particle analyses using field emission scanning electron microscopy with energy-dispersive X-ray spectrometry indicated that the particles were composed mainly of carbon. Prior to amino acid analysis, infrared and Raman microspectroscopy showed some grains possessed primitive organic carbon. Although trace terrestrial contamination, namely l-protein amino acids, was observed in all Hayabusa extracts, several terrestrially uncommon non-protein amino acids were also identified. Some Hayabusa particles contained racemic (d≈l) mixtures of the non-protein amino acids β-aminoisobutyric acid (β-AIB) and β-amino-n-butyric acid (β-ABA) at low abundances ranging from 0.09 to 0.31 nmol g⁻¹. Larger abundances of the non-protein amino acid β-alanine (9.2 nmol g⁻¹, ≈4.5 times greater than background levels) were measured in an extract of three Hayabusa particles. This β-alanine abundance was ≈6 times higher than that measured in an extract of a CM2 Murchison grain processed in parallel. The comparatively high β-alanine abundance is surprising as asteroid Itokawa is similar to amino acid-poor LL ordinary chondrites. Elevated β-alanine abundances and racemic β-AIB and β-ABA in Hayabusa grains suggested these compounds have non-biological and plausibly non-terrestrial origins. These results are the first evidence of plausibly extraterrestrial amino acids in asteroid material from a sample-return mission and demonstrate the capabilities of the analytical protocols used to study asteroid Ryugu and Bennu samples returned by the JAXA Hayabusa2 and NASA OSIRIS-REx missions, respectively.

^1,2Liam S.Morrissey,³D.Pratt,¹W.M.Farrell,¹O.J.Tucker,³S.Nakhla,¹R.M.Killen
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.114979]
¹NASA Goddard Space Flight Center, 20771 Greenbelt, MD, United States
²Catholic University /CRESST II, Washington, DC 20005, United States
³Department of Mechanical Engineering, Memorial University of Newfoundland, A1C 5S7 St. John’s, Newfoundland & Labrador, Canada
Copyright Elsevier

We use molecular dynamics (MD) simulations to better explain the movement of atomic hydrogen in amorphous silica and quantify the planetary science implications of these findings. Previous MD simulations had a large range of predicted values and did not agree well with experiment. Our simulations sample atomic motion for a longer duration and consider a wider range of temperatures than previous simulations. In contrast to constant atomic motion, the hydrogen atoms were shown to undergo random intermittent jumps from one oxygen atom to another, the number of which increase with temperature. Predicted diffusion coefficients had a better agreement to experimental values than previous MD simulations, suggesting the importance of longer simulation durations for better statistics. The low activation energy and jumps observed at lunar temperatures do not support the theory of diurnal variations in OH content for an undamaged amorphous silica surface. Instead, we conclude that energetic solar wind impacts can induce two competing atomic hydrogen motion processes in the exposed surface: A prompt effect that induces jumps in the temperature spike volume, but also a long-term effect of damage in the structure that traps atomic hydrogen. We then use SDTrimSP to quantify the damage created during exposure and MD to demonstrate the H retention and trapping near these defects. Damage was shown to be dependent on impact energy, with defects easily retaining implanted hydrogen. MD results like those presented herein on unweathered surfaces are therefore most relevant to magnetic anomalies. As a result, we demonstrate the importance of lunar volatile models to account for the damage state of the substrate when modelling hydrogen diffusion, retention, and subsequent OH/water production.