¹Eleanor K. Sanson et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13566]
¹School of Earth and Planetary Sciences, Curtin University, Bentley, Western Australia, 6102 Australia
Published by arrangement with John Wiley & Sons

On November 27, 2015, at 10:43:45.526 UTC, a fireball was observed across South Australia by 10 Desert Fireball Network observatories lasting 6.1 s. An ~37 kg meteoroid entered the atmosphere with a speed of 13.68 ± 0.09 km s−1 and was observed ablating from a height of 85 km down to 18 km, having slowed to 3.28 ± 0.21 km s−1. Despite the relatively steep 68.5° trajectory, strong atmospheric winds significantly influenced the darkflight phase and the predicted fall line, but the analysis put the fall site in the center of Kati Thanda–Lake Eyre South. Kati Thanda has meters‐deep mud under its salt‐encrusted surface. Reconnaissance of the area where the meteorite landed from a low‐flying aircraft revealed a 60 cm circular feature in the muddy lake, less than 50 m from the predicted fall line. After a short search, which again employed light aircraft, the meteorite was recovered on December 31, 2015 from a depth of 42 cm. Murrili is the first recovered observed fall by the digital Desert Fireball Network (DFN). In addition to its scientific value, connecting composition to solar system context via orbital data, the recovery demonstrates and validates the capabilities of the DFN, with its next generation remote observatories and automated data reduction pipeline.

^1,2Fabrizio Nestola et al. (>10)
Proceedings of the National Academy of Sciences of the United States of America (in Press) Link to Article [DOI:
https://doi.org/10.1073/pnas.1919067117]
¹Department of Geosciences, University of Padova, I-35131 Padova, Italy
²Geoscience Institute, Goethe University Frankfurt, 60323 Frankfurt, Germany

The origin of diamonds in ureilite meteorites is a timely topic in planetary geology as recent studies have proposed their formation at static pressures >20 GPa in a large planetary body, like diamonds formed deep within Earth’s mantle. We investigated fragments of three diamond-bearing ureilites (two from the Almahata Sitta polymict ureilite and one from the NWA 7983 main group ureilite). In NWA 7983 we found an intimate association of large monocrystalline diamonds (up to at least 100 µm), nanodiamonds, nanographite, and nanometric grains of metallic iron, cohenite, troilite, and likely schreibersite. The diamonds show a striking texture pseudomorphing inferred original graphite laths. The silicates in NWA 7983 record a high degree of shock metamorphism. The coexistence of large monocrystalline diamonds and nanodiamonds in a highly shocked ureilite can be explained by catalyzed transformation from graphite during an impact shock event characterized by peak pressures possibly as low as 15 GPa for relatively long duration (on the order of 4 to 5 s). The formation of “large” (as opposed to nano) diamond crystals could have been enhanced by the catalytic effect of metallic Fe-Ni-C liquid coexisting with graphite during this shock event. We found no evidence that formation of micrometer(s)-sized diamonds or associated Fe-S-P phases in ureilites require high static pressures and long growth times, which makes it unlikely that any of the diamonds in ureilites formed in bodies as large as Mars or Mercury.

¹Shaunna M. Morrison, ¹Robert M. Hazen
American Mineralogist 105, 1508-1535 Link to Article [http://www.minsocam.org/msa/ammin/toc/2020/Abstracts/AM105P1508.pdf]
¹Earth and Planets Laboratory, Carnegie Institution for Science, 5251 Broad Branch Road NW, Washington, D.C. 20015, U. S. A.
Copyright: The Mineralogical Society of America

The evolutionary system of mineralogy relies on varied physical and chemical attributes, including
trace elements, isotopes, solid and fluid inclusions, and other information-rich characteristics, to understand processes of mineral formation and to place natural condensed phases in the deep-time context
of planetary evolution. Part I of this system reviewed the earliest refractory phases that condense at T > 1000 K within the turbulent expanding and cooling atmospheres of highly evolved stars. Part II considers the subsequent formation of primary crystalline and amorphous phases by condensation in three distinct mineral-forming environments, each of which increased mineralogical diversity and distribution prior to the accretion of planetesimals >4.5 billion years ago.
(1) Interstellar molecular solids: Varied crystalline and amorphous molecular solids containing primarily H, C, O, and N are observed to condense in cold, dense molecular clouds in the interstellar medium (10 < T < 20 K; P < 10–13 atm). With the possible exception of some nanoscale organic condensates preserved in carbonaceous meteorites, the existence of these phases is documented primarily by telescopic observations of absorption and emission spectra of interstellar molecules in radio, microwave, or infrared wavelengths. (2) Nebular and circumstellar ice: Evidence from infrared observations and laboratory experiments suggest that cubic H2O (“cubic ice”) condenses as thin crystalline mantles on oxide and silicate dust grains in cool, distant nebular and circumstellar regions where T ~100 K. (3) Primary condensed phases of the inner solar nebula: The earliest phase of nebular mineralogy saw the formation of primary refractory minerals that solidified through high-temperature condensation (1100 < T < 1800 K; 10–6 < P < 10–2 atm) in the solar nebula more than 4.565 billion years ago. These earliest mineral phases originating in our solar system formed prior to the accretion of planetesimals and are preserved in calcium-aluminum-rich inclusions, ultra-refractory inclusions, and amoeboid olivine aggregates.

¹Dominik Talla,¹Madeleine Balla, Claudia Aicher,¹Christian L. Lengauer,¹Manfred Wildner
American Mineralogist 105, 1472-1489 Link to Article [http://www.minsocam.org/msa/ammin/toc/2020/Abstracts/AM105P1472.pdf]
¹Institut für Mineralogie und Kristallographie, Althanstrasse 14, 1090 Wien, Austria
Copyright: The Mineralogical Society of America

The investigation of the presence and role of sulfates in our solar system receives growing attention because these compounds play a crucial role in the water budget of planets such as Mars and significantly influence melting equilibria on the icy moons of Saturn and Jupiter, leading to the formation of subsurface oceans and even cryovolcanism. Despite the dominant presence of higher sulfate hydrates such as epsomite, MgSO4·7H2O, and mirabilite, Na2SO4·10H2O, on these moons’ surfaces, it is not excluded that lower-hydrated sulfates, such as kieserite, MgSO4·H2O, are also present, forming from higher hydrates under pressures relevant to the mantle of the icy moons. Given the composition of the
soluble fraction in C1 and C2 chondritic meteorites, which are high in Ni content and also considered to represent the composition of the rocky cores of the Jovian icy moons, the actual compositions of potentially present monohydrate sulfates likely lie at intermediate values along the solid-solution series between kieserite and transition-metal kieserite-group end-members, incorporating Ni in particular. Moderate Ni contents are also probable in kieserite on Mars due to the planet’s long-term accumulation
of meteoritic nickel, although likely to a much lesser extent than Fe.
Structural and spectroscopic differences between the pure Mg- and Ni-end-members have been previously documented in the literature, but no detailed crystal chemical and spectroscopic investigation along the Mg-Ni solid solution has been done yet. The present work proves the existence of
a continuous (Mg,Ni)SO4·H2O solid-solution series for the first time. It provides a detailed insight into the changes in lattice parameters, structural details, and positions of prominent bands in infrared
(transmission, attenuated total reflectance, diffuse reflectance) and Raman spectra in synthetic samples as the Ni/Mg ratio progresses, at both ambient as well as low temperatures relevant for the icy moons
and Mars. UV-Vis-NIR crystal field spectra of the Ni end-member also help to elucidate the influence of Ni2+-related bands on the overtone- and combination modes.
The (Mg,Ni)SO4·H2O solid-solution series shows Vegard-type behavior, i.e., lattice parameters as well as spectral band positions, change along linear trends with increasing Ni content. Infrared spectra reveal significant changes in the wavenumber positions of prominent bands, depending on the Ni/Mg ratio. We show that the temperature during measurement also has an influence on band position, mainly in the case of H2O-related bands. The changes observed for several absorption features in the
IR spectra enable rough estimation of the Ni/Mg ratio in the monohydrate sulfate, which is applicable to present and future remote sensing data, as well as in situ measurements on Mars or the icy moons.
The spectral features most diagnostic of composition are the vibrational stretching modes of the H2O molecule and a band unique to kieserite-group compounds at around 900 cm–1 in the IR spectra, as well as the pronounced ν3 and ν1 sulfate stretching modes visible in Raman spectra.

¹Michael E. Zolenksy et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13561]
¹ARES, NASA Johnson Space Center, Houston, Texas, 77058 USA
Published by arrangement with John Wiley and Sons

Cosmic ray exposure (CRE) ages of CM chondrites have been found to have multiple peaks (as many as four), in stark contrast to other groups of chondrites (Nishiizumi and Caffee 2012; Herzog and Caffee 2014). In this study, we sought correlations between the CRE ages and petrography of CM chondrites, and we conclude that the degree of aqueous alteration does appear to vary with the CRE ages—the CMs displaying the most aqueous alteration all have relatively short exposure ages. However, some CMs with low degrees of alteration also have short exposure ages—thus, this apparent correlation is not exclusive. We also found a definite inverse relation between the number of distinctive lithologies in a CM and its exposure age, which could indicate different responses of homogeneous and heterogeneous meteoroids to the space environment between their onset of exposure (exhumation and ejection from the parent body) and arrival at Earth. Breccias have more internal surfaces of lithologic discontinuity, possibly resulting in weaker meteoroids that disintegrate more readily than their more homogeneous counterparts. Our results suggest that CM chondrite regoliths consist of numerous genomict lithologies in a breccia with millimeter‐ to decimeter‐scale clasts, with varying degree of heating/metamorphism.

¹Jan L. Hellmann,^1,2Thomas S. Kruijer,¹Knut Metzler,¹Markus Patzek,³Andreas Pack,⁴Jasper Berndt,¹Thorsten Kleine
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13571]
¹Institut für Planetologie, University of Münster, Wilhelm‐Klemm‐Strasse 10, 48149 Münster, Germany
²Nuclear & Chemical Sciences Division, Lawrence Livermore National Laboratory, 7000 East Avenue L‐231, Livermore, California, 94550 USA
³Geowissenschaftliches Zentrum, University of Göttingen, Goldschmidtstr. 1‐3, 37077 Göttingen, Germany
⁴Institut für Mineralogie, University of Münster, Corrensstrasse 24, 48149 Münster, Germany
Published by arrangement with John Wiley & Sons

A large, igneous‐textured, and 2 cm‐sized spherical object from the L5/6 chondrite NWA 8192 was investigated for its chemical composition, petrography, O isotopic composition, and Hf‐W chronology. The petrography and chemical data indicate that this object closely resembles commonly found chondrules in ordinary chondrites and is therefore classified as a “macrochondrule.* As a result of metal loss during its formation, the macrochondrule exhibits elevated Hf/W, which makes it possible to date this object using the short‐lived 182Hf‐182W system. The Hf‐W data provide a two‐stage model age for metal–silicate fractionation of 1.4 ± 0.6 Ma after Ca‐Al‐rich inclusion (CAI) formation, indicating that the macrochondrule formed coevally to normal‐sized chondrules from ordinary chondrites. By contrast, Hf‐W data for metal from the host chondrite yield a younger model age of ~11 Ma after CAIs. This younger age agrees with Hf‐W ages of other type 5–6 ordinary chondrites, and corresponds to the time of cooling below the Hf‐W closure temperature during thermal metamorphism on the parent body. The Hf‐W model age difference between the macrochondrule and the host metal demonstrates that the Hf‐W systematics of the bulk macrochondrule were not disturbed during thermal metamorphism, and therefore, that the formation age of such objects can still be determined even in strongly metamorphosed samples. Collectively, this study illustrates that chondrule formation was not limited to mm‐size objects, implying that the rarity of macrochondrules reflects either that this process was very inefficient, that subsequent nebular size‐sorting decimated large chondrules, or that large precursors were rare.

¹L.Chimiak,²J.E.Elsila,¹B.Dallas,²J.P.Dworkin,^2,3J.C.Aponte,¹A.L.Sessions,¹J.M.Eiler
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.09.026]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, 91125, USA
²Solar System Exploration Division, Code 691, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
¹Department of Chemistry, Catholic University of America, Washington, D.C., 20064
Copyright Elsevier

Meteorites contain prebiotic, bio-relevant organic compounds including amino acids. Their syntheses could result from diverse sources and mechanisms and provide a window on the conditions and materials present in the early solar system. Here we constrain alanine’s synthetic history in the Murchison meteorite using site-specific 13C/12C measurements, reported relative to the VPDB standard. The δ13CVPDB values of –29 ± 10 ‰, 142 ± 20 ‰, and –36 ± 20 ‰ for the carboxyl, amine-bound, and methyl carbons, respectively, are consistent with Strecker synthesis of interstellar-medium-derived aldehydes, ammonia, and low-δ13C nebular or interstellar-medium-derived CN. We report experimentally measured isotope effects associated with Strecker synthesis, and use them to constrain the δ13C values of the alanine precursors, which we then use to construct a model that predicts the molecular-average δ13C values of 19 other organic compounds of prebiotic significance found in Murchison if they were made by our proposed synthetic network. Most of these predictions agree with previous measurements, suggesting that interstellar-medium-derived aldehydes and nebular and/or pre-solar CN could have served as substrates for synthesis of a wide range of prebiotic compounds in the early solar system.

¹C.Pilorget,²J.Fernando,³L.Riu,⁴K.Kitazato,^3,5T.Iwata
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.114126]
¹Institut d’Astrophysique Spatiale, CNRS/Université Paris-Saclay, UMR8617, Orsay 91405, France
²Independent scholar, Orsay 91400, France
³Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara 252-5210, Japan
⁴The University of Aizu, Fukushima, Japan
⁵Department of Space and Astronautical Science, The Graduate University for Advanced Studies, Sokendai, Hayama 240-0193, Japan
Copyright Elsevier

The type C asteroid Ryugu has been visited by the JAXA Hayabusa2 mission, a first for a primitive asteroid in the Solar System exploration. Samples have been collected at its surface by the spacecraft and are now on their way back to Earth. The surface of Ryugu has also been observed both in the visible and infrared wavelengths with the objective of characterizing its properties at a global scale. Here, we report on the albedo and spectro-photometric properties of Ryugu as derived from the NIRS3 IR spectrometer. Thanks to an innovative technique based on a Bayesian approach, we retrieved the Hapke photometric parameters from multi-geometric NIRS3 observations over the NIR spectral range and different areas of Ryugu, including the first collection site. Results reveal an overall spatial homogeneity of the photometric parameters, though some small variations can be highlighted. A new photometric correction was derived and applied to NIRS3 data. Reflectance spatial heterogeneity was quantitatively investigated, in particular by deriving and mapping the single scattering albedo (SSA) at various spatial scales. This parameter could be derived with confidence on about one fourth of Ryugu’s surface, especially around the equatorial region and the southern middle latitudes. Although Ryugu is to first order homogenous with a typical SSA of 0.045–0.050, we demonstrate with a local-scale photometric correction (1) the presence of a large “bright” area between E and E longitude around the equator and the southern middle latitudes, and (2) the presence of darker areas with a clear connection to geomorphological features. We show here that these darker regions tend to have a slightly deeper feature, at least compared to the surrounding areas, which can be explained by an enrichment of the top-surface in dark fines coupled to hydrated phases. Some spatial variability observed in the coupling between the SSA at and the feature also suggests that Ryugu exhibits some (slight) heterogeneity in its building blocks.

¹Arun M.Saranathan,¹Mario Parente
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.114107]
¹Department of Electrical and Computer Engineering, University of Massachusetts, Amherst, United States of America
Copyright Elsevier

The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) has proven instrumental in the mineralogical analysis of the Martian surface. An essential tool for mineral identification for this dataset has been the CRISM summary parameters–which use simple mathematical functions to measure the presence/absence of specific spectral features. While the CRISM summary parameters and browse products (combinations of specific summary parameters) have proven valuable in guiding manual analysis, these hand-crafted representations are not well suited for automated analysis, as CRISM spectral artifacts and noise negatively affect their performance, making these parameters prone to false alarms. We propose an unsupervised technique based on Generative Adversarial Networks (GANs) to learn a more discriminative representation from CRISM data, such that simple metrics in the representation space are sufficient to discriminate between the various mineral spectra present in the data. We describe a simple pipeline using GAN based representations to map mineral signatures of interest across the CRISM image database. We show that the features learned by the GAN are better suited to discriminate mineral signatures in the CRISM database compared to the summary parameters and classical similarity metrics. Finally, we validate the technique over a subset of CRISM images over the Jezero crater and NE Syrtis regions of Mars.

¹Jemma Davidson,²Meenakshi Wadhwa,²Richard L.Hervig,^1,2AliceStephant
Earth and Planetary Science Letters 552, 116597 Link to Article [https://doi.org/10.1016/j.epsl.2020.116597]
¹Center for Meteorite Studies, Arizona State University, 781 East Terrace Road, Tempe, AZ 85287-6004, USA
²School of Earth and Space Exploration, Arizona State University, 781 East Terrace Road, Tempe, AZ 85287-6004, USA
Copyright Elsevier

Determining the source of planetary water from the hydrogen isotope compositions of crustal samples is complicated by the overprinting of isotopically diverse source material by geologic and atmospheric processes. As Mars has no plate tectonics, crustal material, which may have isotopically exchanged with the martian atmosphere, is not recycled into the mantle keeping the water reservoirs in the mantle and atmosphere mostly isolated, buffered by the crust. As the only known martian samples that are regolith breccias with a composition representative of the average crust of Mars, Northwest Africa (NWA) 7034 and its paired stones provide an important opportunity to investigate the water content and hydrogen isotope composition of the martian crust. In particular, apatites in distinct clasts as well as the brecciated matrix of NWA 7034 record a complex history including magmatic and impact processes, and exchange with crustal fluids.