¹Giampaolo P. Sighinolfi,^1,2Federico Lugli,¹Federica Piccione,³Vincenzo DE Michele,^1,4Anna Cipriani
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13550]
¹Department of Chemical and Geological Sciences, University of Modena and Reggio Emilia, Via Campi 103, Modena, 41225 Italy
²Department of Cultural Heritage, University of Bologna, Via degli Ariani 1, Ravenna, 48121 Italy
³Museo di Storia Naturale, Milan, 20121 Italy
⁴Lamont‐Doherty Earth Observatory, Columbia University, Palisades, New York, 10964 USA
Published by arrangement with john Wiley & Sons

Strontium isotopes and selected trace elements (Rb, Sr, REE, Zr, Hf, Th, and U) were measured on samples of Libyan Desert Glass (LDG) and a series of terrestrial materials (rocks, LDG‐bearing soils, eolic sand) collected over a large area of southwestern Egypt to identify the LDG terrestrial parent material and the site where impact melting occurred. Samples include Upper Cretaceous hypersilicic sandstones outcropping at or near the LDG strewn field and Lower Cretaceous to Silurian sandstones from the Gilf Kebir Plateau highlands. Strontium isotopes and partially Zr, Hf, Th, and U, possibly reflecting the composition of detrital zircon grains, are effective indicators of the geochemical affinity between terrestrial materials and LDG, unlike Rb, Sr, and REE abundances. The best geochemical affinity with LDG was found in LDG‐bearing soils collected at the base of intradunal corridors in the Great Sand Sea. Remarkably, abundances of the Zr group elements of the LDG Zr‐bearing phase are distinct from all terrestrial detrital zircons from the area. We suggest a mixture of weathering products from sandstones of different ages, including Devonian and Silurian rocks from the Gilf Kebir highlands, as the most likely source for LDG. A loose sedimentary formation exposed 29 Ma ago at the Earth’s surface, superimposed over hard bedrock, might have been the true terrestrial target of the impact, but because of its incoherent nature, it was rapidly destroyed, explaining the complete absence of any evidence of an impact structure.

^1,2James S. New,³Bahar Kazemi,²Mark C. Price,²Mike J. Cole,²Vassi Spathis,^1,3Richard A. Mathies,²Anna L. Butterworth
Meteoritics & Planetary Science (in Press) Link to Articie [https://doi.org/10.1111/maps.13554]
¹Space Sciences Laboratory, University of California, Berkeley, California, 94720 USA
²School of Physical Sciences, University of Kent, Canterbury, Kent, CT2 7NH UK
³Department of Chemistry, University of California, Berkeley, California, 94720 USA
Published by arrangement with John Wiley & Sons

Enceladus is a compelling destination for astrobiological analyses due to the presence of simple and complex organic constituents in cryovolcanic plumes that jet from its subsurface ocean. Enceladus plume capture during a flyby or orbiter mission is an appealing method for obtaining pristine ocean samples for scientific studies of this organic content because of the high science return, reduced planetary protection challenges, and lower risk and expense compared to a landed mission. However, this mission profile requires sufficient amounts of plume material for sensitive analysis. To explore the feasibility and optimization of the required capture systems, light gas gun experiments were carried out to study organic ice particle impacts on indium surfaces. An organic fluorescent tracer dye, Pacific Blue™, was dissolved in borate buffer and frozen into saline ice projectiles. During acceleration, the ice projectile breaks up in flight into micron‐sized particles that impact the target. Quantitative fluorescence microscopic analysis of the targets demonstrated that under certain impact conditions, 10–50% of the entrained organic molecules were captured in over 25% of the particle impacts. Optimal organic capture was observed for small particles (d ~ 5–15 µm) with velocities ranging from 1 to 2 km s−1. Our results reveal how organic capture efficiency depends on impact velocity and particle size; capture increases as particles get smaller and as velocity is reduced. These results demonstrate the feasibility of collecting unmodified organic molecules from the Enceladus ice plume for sensitive analysis with modern in situ instrumentation such as microfluidic capillary electrophoresis (CE) analysis with ppb organic sensitivity.

^1,2D. Ostrowski,^1,2K. Bryson
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13562]
¹NASA Ames Research Center, Mountain View, California, 94035 USA
²Bay Area Environmental Research Institute, NASA Ames Research Center, Mountain View, California, 94035 USA
Published by arrangement wit John Wiley & Sons

Meteorites provide vast amounts of information on the makeup and history of the solar system. The physical properties help to understand meteor behavior in the atmosphere, model characteristics of parent bodies, and determine methods to deflect potentially hazardous objects. Density and porosity are two of the most important physical properties. All the examined ordinary chondrite falls have bulk densities and porosities near their respected class averages. Most of the studied Antarctic ordinary chondrites have porosities around 12% or higher caused by weathering, placing them near the top of the range of values for chondritic falls. A trend is observed in acoustic velocity, where any meteorite with porosity over 10% has a longitudinal velocity near half the value of the class average. Low porosity meteorites such as Tenham, Chelyabinsk impact melt, and MIL07036 have velocities well above their class averages. Emissivities across all meteorites follow the trend of decreasing emissivity with increasing temperature.

^1,2P.Beck,¹B.Schmitt,¹S.Potin,³A.Pommerol,¹O.Brissaud
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.114066]
¹Institut de Planetologie et d’Astrophysique de Grenoble, UGA-CNRS, France
²Institut Universitaire de France, Paris, France
³Physikalisches Institute, Universität Bern, Sidlerstrasse 5, Bern CH-3012, Switzerland
Copyright Elsevier

Generally, the reflectance of a particulate surface depends on the phase angle at which it is observed. This is true for laboratory measurements on powders of natural materials as well as remote observations of Solar System surfaces. Here, we measured the dependences of reflectance spectra with phase angles, of a suite of 72 meteorites in the 400–2600 nm range. The 10–30° phase angle range is investigated in order to study the contribution of Shadow Hiding Opposition Effect (SHOE) to the phase behavior. The behavior is then extrapolated to phase angle of 0° using a polynomial fit, in order to provide grounds for comparison across meteorite groups (enabling to remove the contribution of shadows to reflectance) as well as to provide “equivalent albedo” values that should be comparable to geometric albedo values derived for small bodies. We find a general behavior of increasing strength of the SHOE with lower reflectance values (whether between samples or for a given samples with absorption features). This trend provides a first order way to correct any reflectance spectra of meteorite powders measured under standard conditions (g = 30°) from the contribution of shadows. The g = 0° calculated reflectance and equivalent albedos are then compared to typical values of albedos for main-belt asteroids. This reveals that among carbonaceous chondrites only Tagish Lake group, CI, and CM chondrites have equivalent albedo compatible with C- and D-type asteroids. On the other hand equivalent albedo derived with CO, CR and CK chondrites are compatible with L- and K-type asteroids. The equivalent albedo derived for ordinary chondrites is related to petrographic types, with low-grade petrographic type (type 3.6 and less) being generally darker that higher petrographic types. This works provides a framework for further understanding of the asteroids meteorite linkage in particular when combining with colors and spectroscopy.

¹Kevin Volk,^1,2G. C. Sloan,³Kathleen E. Kraemer
Astrophysics and Space Science 365, 88 Link to Article [DOI
https://doi.org/10.1007/s10509-020-03798-2]
¹Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218, USA
²Department of Physics and Astronomy, University of North Carolina, Chapel Hill, USA
³Boston College, Institute for Scientific Research, 140 Commonwealth Avenue, Chestnut Hill, MA, 02467, USA

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¹Andreas Morlok,¹Benjamin Schiller,¹Iris Weber,²Mohit Melwani Daswani,¹Aleksandra N.Stojic,¹Maximilian P.Reitze,¹Tim Gramse,³Stephen D.Wolters,¹Harald Hiesinger,³Monica M.Grady,⁴Joern Helbert
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2020.105078]
¹Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, 48149, Münster, Germany
²Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr, Pasadena, CA, 91109, USA
³School of Physical Sciences, Open University, Milton Keynes, MK76AA, UK
⁴Institute for Planetary Research, DLR, Rutherfordstrasse 2, 12489, Berlin, Germany

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¹Mason B.Gardner,¹Brent R.Westbrook,¹Ryan C.Fortenberry
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2020.105076]
¹University of Mississippi, Department of Chemistry & Biochemistry, University, MS, 38677, U.S.A

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¹Brandon P. Rasmussen,¹Wendy M. Calvin,^2,5Bethany L. Ehlmann,³Thomas F. Bristow,⁴Nicole Lautze,⁵Abigail A. Fraeman,¹Joel W. DesOrmeau
American Mineralogist105, 1306-1316 Link to Article [http://www.minsocam.org/msa/ammin/toc/2020/Abstracts/AM105P1306.pdf]
¹Department of Geological Sciences, University of Nevada, Reno, Nevada 89577, U.S.A.
²Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A.
³NASA Ames Research Center, Moffett Field, California 94035, U.S.A.
⁴School of Ocean and Earth Science and Technology, University of Hawaii at Manoa, Honolulu, Hawaii 96822, U.S.A.
⁵Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, U.S.A.
Copyright: The Mineralogical Society of America

We performed a multi-scale characterization of aqueous alteration of Mars analog basaltic rock from a Mauna Kea drill core using high-resolution visible and short-wave infrared (VIS-SWIR) spectral imaging, scanning electron microscopy, X‑ray diffraction, and point VIS‑SWIR spectra. Several types of smectites, zeolites, and primary minerals were identified. Mineral classes were mapped in cut sec-tions extracted from the drill core and used to represent the range of alteration products seen in field data collected over 1000 m depth (Calvin et al. 2020). Ten distinct spectral end‑members identified in the cut sections were used to map the field point spectra. Trioctahedral Fe‑ and Mg‑rich smectites were present toward the top of the zone of analysis (972 m below the surface) and increased in abundance toward the bottom of the drill core (1763 m depth). The mineralogy demonstrates a general trend of discontinuous alteration that increases in intensity with depth, with less pervasive phyllosilicate alteration at the top, several zones of different mixtures of zeolites toward the center, followed by more abundant phyllosilicates in the lowest sections. Distinctly absent are Fe‑Mg phyllosilicates other than smectites, as well as carbonates, sulfates, and Al phyllosilicates such as kaolinite or illite. Furthermore, hematite was only detected in two of 24 samples. The suite of assemblages points to aqueous alteration at low-to-moderate temperatures at neutral to basic pH in low-oxygen conditions, with little evidence of extensive surface interaction, presenting a possible analog for an early Mars subsurface environment. We also present a library of VIS-SWIR spectra of the analyzed cut sections, including both spatial averages (i.e., unweighted linear mixtures) of spectral images of each cut section and single point spectra of the cut sections. This will allow for consideration of nonlinear mixing ef-fects in point spectra of these assemblages from natural surfaces in future terrestrial or planetary work.

¹Wendy M. Calvin,²Nicole Lautze,³Joe Moore,²Donald Thomas,²Eric Haskins,¹Brandon P. Rasmussen
American Mineralogist 105, 1297–1305 Link to Article [http://www.minsocam.org/msa/ammin/toc/2020/Abstracts/AM105P1297.pdf]
¹Department of Geological Sciences, University of Nevada, Reno, Nevada 89577, U.S.A.
²Hawaii Institute of Geophysics and Planetology, University of Hawaii, Honolulu, Hawaii 96822, U.S.A.
³Energy and Geoscience Institute, University of Utah, Salt Lake City, Utah, 84108, U.S.A.
Copyright: The Mineralogical Society of America

Continuous rock core was collected for 1764 m (5786’) on the Pohakuloa Army Training base near the center of the big island of Hawaii. The core traverses basaltic lava flows from the volcano’s shield-building phase, and perched aquifers and higher temperature groundwaters were encountered. The collected samples record water-rock interactions of basaltic materials in a setting that may be a model for groundwater interactions on Mars. We collected visible and infrared point spectra of materials in the lowest portion of the core, where alteration was noted to become more prominent. We identi-fied three types of phyllosilicate spectral signatures and three types of zeolites. The phyllosilicates show similarity to those identified on Mars using data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). Based on the field survey, 25 depths were selected for sampling and petrographic analysis of thin sections. The spectral data and thin section work have a strong agreement in the types of materials identified by the two different techniques. Both the spectral and petrographic data indicate low to moderate temperature geothermal alteration occurred in the lower half of the core. The field spectra are a useful reconnaissance tool for selecting mineralogic diversity for subsequent higher resolution and more time-consuming laboratory analysis.

¹Ryuki Hyodo,²Hidenori Genda,²Ramon Brasser
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.114064]
¹ISAS, JAXA, Sagamihara, Japan
²Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo 152-8550, Japan
Copyright Elsevier

Late accretion is a process that strongly modulated surface geomorphic and geochemical features of Mercury. Yet, the fate of the impactors and their effects on Mercury’s surface through the bombardment epoch are not clear. Using Monte-Carlo and analytical approaches of cratering impacts, we investigate the physical and thermodynamical outcomes of late accretion on Mercury. Considering the uncertainties in late accretion, we develop scaling laws for the following parameters as a function of impact velocity and total mass of late accretion: (1) depth of crustal erosion, (2) the degree of resurfacing, and (3) mass accreted from impactor material. Existing dynamical models indicate that Mercury experienced an intense impact bombardment (a total mass of ∼8 × 1018 − 8 × 1020 kg with a typical impact velocity of 30 − 40 km s−1) after 4.5 Ga. For this parameter range, we find that late accretion could remove 50 m to 10 km of the early (post-formation) crust of Mercury, but the change to its core-to-mantle ratio is negligible. Alternatively, the mantles of putative differentiated planetesimals in the early solar system could be more easily removed by impact erosion and their respective core fraction increased, if Mercury ultimately accreted from such objects. Although the cratering is notable for erasing the older geological surface records on Mercury, we show that ∼40 − 50wt. % of the impactor’s exogenic materials, including the volatile-bearing materials, can be heterogeneously implanted on Mercury’s surface as a late veneer (at least 3 × 1018 − 1.6 × 1019 kg in total). About half of the accreted impactor’s materials are vaporized, and the rest is completely melted upon the impact. We expect that the further interplay between our theoretical results and forthcoming surface observations of Mercury, including the BepiColombo mission, will lead us to a better understanding of Mercury’s origin and evolution.