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.

¹C.Xiang,¹A.Carballido,¹L.S.Matthews,¹T.W.Hyde
Icarus (in Press) Linkto Article [https://doi.org/10.1016/j.icarus.2020.114053]
¹Center for Astrophysics, Space Physics, and Engineering Research, Baylor University, Waco, TX 76798-7316, USA
Copyright Elsevier

In order to characterize the early growth of fine-grained dust rims (FGRs) that commonly surround chondrules, we simulate the growth of FGRs through direct accretion of monomers of various sizes onto the chondrule surfaces. Dust becomes charged to varying degrees in the radiative plasma environment of the solar nebula (SN), and the resulting electrostatic force alters the trajectories of colliding dust grains, influencing the structure of the dust rim as well as the time scale of rim formation. We compare the growth of FGRs in protoplanetary disks (PPD) with different turbulence strengths and plasma conditions to previous models which assumed neutral dust grains (Xiang, C., Carballido, A., Hanna, R.D., Matthews, L.S., Hyde, T.W., 2019). We use a combination of a Monte Carlo method and an N-body code to simulate the collision of dust monomers of radii 0.5 – m with chondrules whose radii are between 500 and m: a Monte Carlo algorithm is used to randomly select dust particles that will collide with the chondrule as well as determine the elapsed time interval between collisions; at close approach, the detailed collision process is modeled using an N-body algorithm, Aggregate Builder (AB), to determine the collision outcome, as well as any restructuring of the chondrule rim. For computational expediency, we limit accretion of dust monomers to a small patch of the chondrule surface. The collisions are driven by Brownian motion and coupling to turbulent gas motion in the protoplanetary disk. The charge distribution of the dust rim is modeled, used to calculate the trajectories of dust grains, and then analyze the resulting morphology of the dust rim. In a weakly turbulent region, the decreased relative velocity between charged particles causes small grains to be repelled from the chondrule, causing dust rims to grow more slowly and be composed of larger monomers, which results in a more porous structure. In a highly turbulent region, the presence of charge mainly affects the porosity of the rim by causing dust particles to deviate from the extremities of the rim and reducing the amount of restructuring caused by high-velocity collisions.

¹Libby D. Tunney,¹Christopher D. K. Herd,^1,2Robert W. Hilts
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13551]
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

The study of organic compounds in astromaterials represents a unique window into organic matter in the interstellar medium, the solar nebula, and asteroid parent bodies, and insights into pathways that may relate organic matter in these diverse environments. Unfortunately, the Earth’s surface is awash in organic material, which forms a significant source of contamination, especially for specimens of meteorite falls. Here, we employ specimens of the Buzzard Coulee H4 ordinary chondrite, the fall of which in western Saskatchewan, Canada, on November 20, 2008 was widely documented, and from which meteorites were recovered starting shortly after the fall and continuing to over 10 years later. The low intrinsic organic matter content of these H4 specimens enables their use as “blanks” for terrestrial contamination. Using dichloromethane rinses of meteorite specimen exteriors, and analysis of organic compounds by gas chromatograph‐mass spectrometry, we document the sources of terrestrial contamination as a function of location, time of collection relative to the fall, and curation and handling since collection. We find numerous terrestrial organic compounds, most of which can be attributed to the terrestrial surface on which the meteorite specimens were collected, and we consider a variety of factors that may influence the degree of contamination. To determine the source of each contaminant more accurately, we advocate for the collection of terrestrial materials (e.g., soil, vegetation) alongside meteorites. Our results have implications for how specimens from meteorite falls—especially for meteorites expected to have high intrinsic organic content—are collected, documented, and curated.

¹Laurette Piani,¹Yves Marrocchi,¹Thomas Rigaudier,^1,2Lionel G. Vacher,¹Dorian Thomassin,¹Bernard Marty
Science 369, 1110-1113 Link to Article [DOI: 10.1126/science.aba1948
Article]
¹Centre de Recherches Pétrographiques et Géochimiques (CRPG), Centre National de Recherche Scientifique (CNRS)–Université de Lorraine, Vandoeuvre-les-Nancy, F-54500, France.
²Department of Physics, Washington University in St. Louis, St. Louis, MO 63130, USA.
Reprinted with permission from AAAS

The origin of Earth’s water remains unknown. Enstatite chondrite (EC) meteorites have similar isotopic composition to terrestrial rocks and thus may be representative of the material that formed Earth. ECs are presumed to be devoid of water because they formed in the inner Solar System. Earth’s water is therefore generally attributed to the late addition of a small fraction of hydrated materials, such as carbonaceous chondrite meteorites, which originated in the outer Solar System where water was more abundant. We show that EC meteorites contain sufficient hydrogen to have delivered to Earth at least three times the mass of water in its oceans. EC hydrogen and nitrogen isotopic compositions match those of Earth’s mantle, so EC-like asteroids might have contributed these volatile elements to Earth’s crust and mantle.

¹G.David et al. (>10)
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2019JE006314]
¹Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, UPS, CNRS, CNES, Toulouse, France
Published by arrangement with John Wiley & Sons

Curiosity investigated a topographic rise named Vera Rubin ridge (VRR) in Gale crater, for which a distinct hematite‐like signature was observed from orbit. However, the ChemCam and APXS instruments on board the rover did not record any significant iron enrichment in the bulk of the ridge compared to previous terrains. For this study, we have re‐verified ChemCam iron calibration at moderate abundances and developed more accurate calibrations at high‐iron abundances using iron oxide mixtures in a basaltic matrix in order to complete the ChemCam calibration database. The high‐iron calibration was first applied to the analysis of dark‐toned diagenetic features encountered at several locations on VRR, which showed that their chemical compositions are close to pure anhydrous iron oxides. Then, we tracked iron abundances in the VRR bedrock and demonstrated that although there is no overall iron enrichment in the bulk of the ridge (21.2±1.8 wt.% FeO_T) compared to underlying terrains, the iron content is more variable in its upper section with areas of enhanced iron abundances in the bedrock (up to 26.6±0.85 wt.% FeO_T). Since the observed variability in iron abundances does not conform to the stratigraphy, the involvement of diagenetic fluid circulation was likely. An in‐depth chemical study of these Fe‐rich rocks reveals that spatial gradients in redox potential (Eh) may have driven iron mobility and reactions that precipitated and accumulated iron oxides. We hypothesize that slightly reducing fluids were probably involved in transporting ferrous iron. Mobile Fe²⁺ could have precipitated as iron oxides in more oxidizing conditions.

¹Rebecca N. Greenberger,^1,2Bethany L. Ehlmann,^3,4Gordon R. Osinski,^3,4Livio L. Tornabene,²Robert O. Green
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2019JE006218]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
³Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada
⁴Institute for Earth and Space Exploration, University of Western Ontario, London, Ontario, Canada
Published by arrangement with John Wiley & Sons

Connecting the surface expression of impact crater‐related lithologies to planetary or regional subsurface compositions requires an understanding of material transport during crater formation. Here, we use imaging spectroscopy of 6 clast‐rich impact melt rock outcrops within the well‐preserved 23.5‐Ma, 23‐km diameter Haughton impact structure, Canada, to determine melt rock composition and spatial heterogeneity. We compare results from outcrop to outcrop, using clasts, groundmass, and integrated clast‐groundmass compositions as tracers of transport during crater‐fill melt rock formation and cooling. Supporting laboratory imaging spectroscopy analyses of 91 melt‐bearing breccia and clast samples and microscopic x‐ray fluorescence elemental mapping of cut samples paired with spectroscopy of identical surfaces validate outcrop‐scale lithological determinations. Results show different clast‐rich impact melt rock compositions at three sites kilometers apart and an inverse correlation between silica‐rich (sandstone, gneiss, and phyllosilicate‐rich shales) and gypsum‐rich rocks that suggests differences in source depth with location. In the target stratigraphy, gypsum is primarily sourced from ~1 km depth, while gneiss is from >1.8 km depth, sandstone from >1.3 km, and shales from ~1.6–1.7 km. Observed heterogeneities likely result from different excavation depths coupled with rapid quenching of the melt due to high content of cool clasts. Results provide quantitative constraints for numerical models of impact structure formation and give new details on melt rock heterogeneity important in interpreting mission data and planning sample return of impactites, particularly for bodies with impacts into sedimentary and volatile‐bearing targets, e.g., Mars and Ceres.

¹E.K.Kolesnikov,²A.G.Zelensky
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2020.105065]
¹St. Petersburg State University, St. Petersburg, 198504 Russia
²Moscow State Technical University of Civil Aviation, Moscow, 125493 Russia

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