^1,2S. R. Sutton,³A. J. Brearley,^3,4E. DobricĂ,¹A. Lanzirotti,¹M. Newville,⁵O. Tschauner
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13603]
¹Center for Advanced Radiation Sources, University of Chicago, Chicago, Illinois, 60637 USA
²Department of the Geophysical Sciences, University of Chicago, Chicago, Illinois, 60637 USA
³Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, 87131 USA
⁴Hawai’i Institute of Geophysics and Planetology, School of Ocean, Earth Science, and Technology, University of Hawai’i at Mānoa, Honolulu, Hawaii, 96822 USA
⁵Department of Geoscience, University of Nevada, Las Vegas, Nevada, 89154 USA
Published by arrangement with John Wiley & Sons

X‐ray absorption fine structure (XAFS) spectroscopy methods have been applied to focused ion beam (FIB) produced sections of olivine and pyroxene for determining the valence states of Ti, V, and Cr and inferring oxygen fugacities of formation for each element. High‐quality XAFS spectra were obtained for all three elements for analytical voxels of ~10 pg and usable spectra down to the pg level are achievable. The extraterrestrial samples studied here were olivine and pyroxene from chondrules in Semarkona (LL3.00), olivine from chondrules in Kainsaz (CO3.2), and an olivine and a pyroxene grain from two Antarctic micrometeorites (AMM). The general agreement between calculated thin section and FIB section valences strongly suggests that there is negligible alteration of Ti, V, and Cr valences during FIB sectioning. The inferred oxygen fugacities for the AMM olivine support an equilibrium igneous history similar to results seen for some achondrites. For the pyroxene, highly reduced Cr, coupled with relatively oxidized Ti, suggests an origin in a mildly metamorphosed chondritic parent body. These results demonstrate that this FIB and micro‐XAFS approach is promising for establishing the oxidation states of minute monomineralic grains of diverse extraterrestrial origins, including materials from sample‐return spacecraft, such as the Stardust, OSIRIS‐REx, Hayabusa, and Hayabusa2 missions.

¹Nicola J.Potts,^1,2Geoffrey D.Bromiley,³Richard A.Brooker
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.12.003]
¹School of GeoSciences, Grant Institute, University of Edinburgh, Edinburgh, UK
²Centre for Science at Extreme Conditions, University of Edinburgh, UK
³School of Earth Sciences, University of Bristol, Bristol, UK
Copyright Elsevier

It is believed that the Moon formed following collision of a large planetesimal with the early Earth. Over the ∼4 Gyr since this event the Moon has been considerably less processed by geological activity than the Earth, and may provide a better record of processes and conditions in the early Earth-Moon system. There have been many studies of magmatic volatiles such as H, F, Cl, S and C in lunar materials. However, our ability to interpret variable volatile contents in the lunar sample suite is dependent on our understanding of volatile behaviour in lunar systems. This is currently constrained by limited experimental data. Here, we present the first experimental mineral-melt partitioning coefficients for F, Cl and H2O in a model lunar system under appropriately reduced conditions (log fO2 to IW-2.1, i.e. oxygen fugacity down to 2.1 log units below the Fe-FeO buffer). Data are consistent with structural incorporation of F, Cl and OH- in silicate melt, olivine and pyroxene under conditions of the lunar mantle. Oxygen fugacity has a limited effect on H2O speciation, and partitioning of H2O, F and Cl is instead largely dependent on mineral chemistry and melt structure. Partition coefficients are broadly consistent with a mantle source region for lunar volcanic products that is significantly depleted in F, Cl and H2O, and depleted in Cl relative to F and H2O, compared to the terrestrial mantle. Partitioning data are also used to model volatile redistribution during lunar magma ocean (LMO) crystallisation. The volatile content of lunar mantle cumulates is dependent upon proportion of trapped liquid during LMO solidification. However, differences in mineral-melt partitioning during LMO solidification can result in significant enrichment on F relative to Cl, and F relative to H2O, in cumulate phases relative to original LMO composition. As such, Cl depletion in lunar volcanic products may in part be a result of LMO solidification.

¹Amar Agarwal,¹Satyendra Kumar,²Gaurav Joshi,²K. K. Agarwal
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13604]
¹Department of Earth Sciences, Indian Institute of Technology‐Kanpur, Kanpur, 208016 India
²Centre of Advanced Study in Geology, University of Lucknow, Lucknow, 226007 India
Published by arrangement with John Wiley & Sons

The central elevated area is a postimpact morphological landmark in the otherwise flat eroded remnant of the Dhala impact structure, India. Its base is the Bundelkhand granitic complex followed by beds of Dhala and Kaimur Formations. The beds of the Dhala and Kaimur Formation present typical sedimentary textures and structures such as cross‐bedding. The grains are angular, sorting is moderate to poor, and brittle–ductile deformation of the protolith is still preserved in some grains. This reveals a short distance of transport. Detailed microscopy and U‐stage measurements confirm planar deformational features (PDFs) oriented (0001) and {10–13} in few quartz grains. Based on these facts, it is suggested that the quartz with PDFs was shocked, ejected out of the crater, and deposited near the crater cavity. Reworking of the ejecta blanket redeposited these quartz grains to their present location. Relatively few shocked grains in the rocks favor a postimpact fluvial process over impact resurge.

¹J.D.P.Deshapriya et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.114252]
¹LESIA, Observatoire de Paris, Université PSL, CNRS, Université de Paris, Sorbonne Université, 5 place Jules Janssen, 92195 Meudon, France
Copyright Elsevier

Using data acquired by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) mission, we investigate spectral properties of craters on the near-Earth asteroid (101955) Bennu. We compare Bennu’s craters with its global average by means of four spectral parameters: (a) minimum position of the band at 2.7 μm, (b) depth of the hydrated phyllosilicate absorption band at 2.7 μm, (c) normalized spectral slope from 0.55 to 2.0 μm, and (d) reflectance factor at 0.55 μm. We examine 45 craters using spectral data obtained under various observing conditions. For 20 craters, we find a shortward shift of the 2.7-μm band minimum relative to the global 2.7-μm band minimum, which we attribute to the presence of relatively fresh (less space-weathered) material excavated from the sub-surface by crater-forming impacts. For three craters, we find an anti-correlation between spectral slopes and reflectance factor for a series of spectra acquired during a specific scan, where we observe that spectra become redder and darker towards the center of the crater. We attribute this to the presence of fine-particulate regolith. Localized spectral heterogeneities are apparent inside a prominent equatorial crater on Bennu, which is one of the asteroid’s oldest geological features. We propose that such local spectral heterogeneities could be used as a tracer of mass movement on Bennu. We show that younger craters are redder, brighter, and have deeper 2.7-μm bands. Comparing global average spectral values of Bennu and crater frequency distributions as a function of the chosen spectral parameters, we find that craters evolve to assume the global average spectral properties of Bennu. A positive correlation identified between the reflectance factor and 2.7-μm band depth suggests that brighter craters tend to be more hydrated. Finally, we put into context, the results from the Small Carry-on Impactor experiment by the Hayabusa2 spacecraft, which created an artificial crater on the near-Earth asteroid (162173) Ryugu.

¹Jeffrey R.Johnson,²William M.Grundy,³Mark T.Lemmon,⁴W.Liang,⁵James F.BellIII,⁶A.G.Hayes,⁷R.G.Deen
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.114261]
¹Johns Hopkins University Applied Physics Laboratory, Laurel, MD, United States of America
²Lowell Observatory, Flagstaff, AZ, United States of America
³Space Science Institute, Boulder, CO, United States of America
⁴Lunar and Planetary Laboratory, Tucson, AZ, United States of America
⁵Arizona State University, Tempe, AZ, United States of America
⁶Cornell University, Ithaca, NY, United States of America
⁷Jet Propulsion Laboratory, Pasadena, CA, United States of America
Copyright Elsevier

The last sets of panoramic camera (Pancam) visible/near-infrared (432–1009 nm) multispectral observations made under varying viewing and illumination geometries by the Mars exploration rovers Spirit and opportunity were examined using radiative transfer models to study the surface scattering and microphysical nature of rock and soil units at both sites. Nearly 12,000 individual measurements were collected for this study of soil, dust, and rock units over phase angles of ~0° to ~150°. Images were acquired on sols 1944–1946 (June 2009) at Troy, the final resting place of Spirit on the western side of home plate in Gusev crater, and by opportunity at three locations on the western rim of Endeavour crater in Meridiani Planum between sols 2785 (November 2011) and 3867 (December 2014). Sky models were developed from observations of atmospheric opacity, which enabled corrections for diffuse skylight when combined with surface facet orientations determined from stereo images. Model results were improved by removing data affected by scattered light evident in some high phase angle images (resulting from minor dust contamination on the camera windows). At Troy, relatively dust-free “gray” rock units exhibited narrow, forward scattering behaviors akin to previous analyses of similar gray rock units at Gusev crater. Soils and “red” rocks coated with greater amounts of dust were more backscattering. Red rocks exhibited higher single scattering albedo (w), macroscopic roughness (), and opposition effect width (h) parameters, indicative of rough, low-porosity surfaces perhaps with more uniform grain size distributions. At Meridiani Planum, rubbly soils near São Gabriel crater and Cape Tribulation exhibited w values typical of previous soil analyses. However, the large drift “dust” deposits found in depressions on the northern tip of Cape York near Turkey haven demonstrated elevated w values with a downturn toward 1009 nm, consistent with minor hydration of these materials. The dust deposits were modeled with the lowest values and highest h values of all soil units analyzed during the opportunity mission, indicative of a smooth surface with homogeneous grain size distribution and/or lower porosity than other units. The dust unit scattering function was dissimilar to those for atmospheric and airfall-deposited dusts, however, suggesting that the originally deposited materials had been modified, perhaps by hydration and ongoing aeolian effects. Analyses of phase curve ratios among the units studied here and from laboratory data of analog soils suggested that surface scattering is a major control on the peak phase angle position of the “arch” in phase curve ratios, alongside the effects of particle-scale roughness

¹Maria M. Costa (>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.2016326117]
¹Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, 1350 Copenhagen, Denmark

Combining U–Pb ages with Lu–Hf data in zircon provides insights into the magmatic history of rocky planets. The Northwest Africa (NWA) 7034/7533 meteorites are samples of the southern highlands of Mars containing zircon with ages as old as 4476.3 ± 0.9 Ma, interpreted to reflect reworking of the primordial Martian crust by impacts. We extracted a statistically significant zircon population (n = 57) from NWA 7533 that defines a temporal record spanning 4.2 Gyr. Ancient zircons record ages from 4485.5 ± 2.2 Ma to 4331.0 ± 1.4 Ma, defining a bimodal distribution with groupings at 4474 ± 10 Ma and 4442 ± 17 Ma. We interpret these to represent intense bombardment episodes at the planet’s surface, possibly triggered by the early migration of gas giant planets. The unradiogenic initial Hf-isotope composition of these zircons establishes that Mars’s igneous activity prior to ∼4.3 Ga was limited to impact-related reworking of a chemically enriched, primordial crust. A group of younger detrital zircons record ages from 1548.0 ± 8.8 Ma to 299.5 ± 0.6 Ma. The only plausible sources for these grains are the temporally associated Elysium and Tharsis volcanic provinces that are the expressions of deep-seated mantle plumes. The chondritic-like Hf-isotope compositions of these zircons require the existence of a primitive and convecting mantle reservoir, indicating that Mars has been in a stagnant-lid tectonic regime for most of its history. Our results imply that zircon is ubiquitous on the Martian surface, providing a faithful record of the planet’s magmatic history.

^1,2Jan Render,²Gregory A.Brennecka
Earth and Planetary Science Letters 555, 116705 Link to Article [https://doi.org/10.1016/j.epsl.2020.116705]
¹Institut für Planetologie, University of Münster, Wilhelm-Klemm-Straße 10, Münster, 48149, Germany
²Nuclear and Chemical Sciences Division, Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA, USA
Copyright Elsevier

The significant reorganization of the early Solar System due to giant planet migration has hampered our understanding of where planetary bodies formed. Previously employed proxies for reconstructing the primordial planetary architecture, such as water content or oxidation state, are complicated by post-accretionary processes. Here we investigate basaltic achondrites for their nucleosynthetic isotope signatures in the elements neodymium (Nd) and zirconium (Zr) and show that they are—similar to previously investigated chondritic meteorites—characterized by a relative deficit in isotopes produced by the s-process of nucleosynthesis. Importantly, these data are well correlated with nucleosynthetic signatures observed in other elements, demonstrating that s-process matter was heterogeneously distributed throughout the early Solar System. By comparing these isotopic signatures with potential proxies for Solar System reconstruction and computer modeling, we here argue that this isotopic heterogeneity in bulk meteoritic materials is linked to the original heliocentric distance of formation. Such scaling of nucleosynthetic signatures with heliocentric distance could permit reconstruction of the primordial architecture of the Solar System by ‘cosmolocating’ the accretion orbits of meteoritic parent bodies as a function of incorporated s-process matter.

^1,2Richter, W.A.,^3,9Brown, B.A.,^4,5Longland, R.,^3,9Wrede,C.,⁶Denissenkov, P.,³Fry, C.,^5,9Herwig, F.,⁷Kurtulgil, D.,^8,9,10Pignatari, M.,⁶Reifarth, R.
Physical Review C 102, 025801 Link to Article [DOI: 10.1103/PhysRevC.102.025801]
¹University of Stellenbosch, Stellenbosch, 7600, South Africa
²IThemba LABS, Somerset West, 7130, South Africa
³Department of Physics and Astronomy, National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824-1321, United States
⁴Department of Physics, North Carolina State University, Raleigh, NC 27695, United States
⁵Triangle Universities Nuclear Laboratory, Duke University, Durham, NC 27710, United States
⁶Department of Physics and Astronomy, University of Victoria, Victoria, BC V8W 2Y2, Canada
⁷Goethe University Frankfurt, Max-von-Laue-Strasse 1, Frankfurt am Main, 60438, Germany
⁸E.A. Milne Center for Astrophysics, Department of Physics and Mathematics, University of Hull, Hull, HU6 7RX, United Kingdom
⁹Konkoly Observatory, Research Center for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Konkoly Thege Miklos ut 15-17, Budapest, H-1121, Hungary
¹⁰Joint Institute for Nuclear Astrophysics, Center for the Evolution of the Elements, Michigan State University, East Lansing, MI 48824, United States

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Li, Y. et al. (>10)
Physical Review C 102 Link to Article [DOI: 10.1103/PhysRevC.102.025804]
¹China Institute of Atomic Energy, P. O. Box 275(10), Beijing, 102413, China

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Michael S.Bramble,¹Ralph E.Milliken,²William R.PattersonIII
Icarus (in Press) Link to Journal [https://doi.org/10.1016/j.icarus.2020.114251]
¹Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI, USA
²School of Engineering, Brown University, Providence, RI, USA
Copyright Elsevier

We investigate a suite of synthetic mineral mixtures designed to act as bulk mineralogical analogs to H, L, and LL ordinary chondrite meteorites in order to probe how the thermal emission characteristics of such materials change between ambient and simulated asteroid environmental conditions. Due to the parent body link with certain S-type asteroids, studying these analog mixtures in an environment that is relevant to actual asteroid surfaces advances our understanding of the thermal emission properties of one of the most common regolith types among the main-belt and near-Earth asteroid populations. The observed changes in spectral emissivity features due to cold, vacuum conditions are not as large as previously observed for single mineral (silicate) samples. We interpret this difference to be the result of metallic and opaque components weakening near-surface thermal gradients in the mixtures. As such, we predict that near-surface thermal gradients on ordinary chondrite parent bodies (e.g., S-type asteroids) are likely much weaker than would be inferred from cold, vacuum measurements of individual mineral components. We tested whether the increased spectral contrast observed in fine-grained (<25 μm) samples measured in a cold, vacuum environment increases the efficacy of least squares linear unmixing methods. It is found that the accuracy of such models does not improve relative to measurements made under ambient conditions, thus linear unmixing models are not expected to yield accurate estimates of the modal mineralogy of airless planetary surfaces if they are dominated by fine-grained regolith. Mixtures with coarse particle sizes (125–250 μm) that were modeled using the coarse particle size endmembers yielded results that were largely independent of the environmental conditions, but with larger errors in spectral fits for samples measured in a simulated asteroid environment. At simulated asteroid environmental conditions, the bulk silicate composition and metal content play a more important role in determining the thermal state and brightness temperature of the sample than at ambient conditions. Modest changes in metal content (10–25 wt%) lead to large differences in the brightness temperature of a sample. Under simulated asteroid conditions, an ~10 K increase in maximum brightness temperature that tracks with increased iron content is observed at fine particle sizes (<25 μm) between each of the analog ordinary chondrite groups. Based on these results, it may be difficult to distinguish H, L, and LL compositions of suspected ordinary chondrite parent bodies using only Earth- or space-based thermal emission spectra. This is inferred from the spectral similarity of the analog mixtures and the absence of significant variation in spectral emissivity associated with reported differences in bulk metal content for ordinary chondrites.