¹Roger C. Wiens et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113897]
¹Los Alamos National Laboratory, Los Alamos, NM, USA
Copyright Elsevier

Heterolithic, boulder-containing, pebble-strewn surfaces occur along the lower slopes of Aeolis Mons (“Mt. Sharp”) in Gale crater, Mars. They were observed in HiRISE images acquired from orbit prior to the landing of the Curiosity rover. The rover was used to investigate three of these units named Blackfoot, Brandberg, and Bimbe between sols 1099 and 1410. These unconsolidated units overlie the lower Murray formation that forms the base of Mt. Sharp, and consist of pebbles, cobbles and boulders. Blackfoot also overlies portions of the Stimson formation, which consists of eolian sandstone that is understood to significantly postdate the dominantly lacustrine deposition of the Murray formation. Blackfoot is elliptical in shape (62 × 26 m), while Brandberg is nearly circular (50 × 55 m), and Bimbe is irregular in shape, covering about ten times the area of the other two. The largest boulders are 1.5–2.5 m in size and are interpreted to be sandstones. As seen from orbit, some boulders are light-toned and others are dark-toned. Rover-based observations show that both have the same gray appearance from the ground and their apparently different albedos in orbital observations result from relatively flat sky-facing surfaces.

Chemical observations show that two clasts of fine sandstone at Bimbe have similar compositions and morphologies to nine ChemCam targets observed early in the mission, near Yellowknife Bay, including the Bathurst Inlet outcrop, and to at least one target (Pyramid Hills, Sol 692) and possibly a cap rock unit just north of Hidden Valley, locations that are several kilometers apart in distance and tens of meters in elevation. These findings may suggest the earlier existence of draping strata, like the Stimson formation, that would have overlain the current surface from Bimbe to Yellowknife Bay. Compositionally these extinct strata could be related to the Siccar Point group to which the Stimson formation belongs.

Dark, massive sandstone blocks at Bimbe are chemically distinct from blocks of similar morphology at Bradbury Rise, except for a single float block, Oscar (Sol 516). Conglomerates observed along a low, sinuous ridge at Bimbe consist of matrix and clasts with compositions similar to the Stimson formation, suggesting that stream beds likely existed nearly contemporaneously with the dunes that eventually formed the Stimson formation, or that they had the same source material. In either case, they represent a later pulse of fluvial activity relative to the lakes associated with the Murray formation.

These three units may be local remnants of infilled impact craters (especially circular-shaped Brandberg), decayed buttes, patches of unconsolidated fluvial deposits, or residual mass-movement debris. Their incorporation of Stimson and Murray rocks, the lack of lithification, and appearance of being erosional remnants suggest that they record erosion and deposition events that post-date the exposure of the Stimson formation.

¹Dominik Spahr et al (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113898]
¹Institute of Geosciences, Goethe University Frankfurt, Altenhöferallee 1, 60438 Frankfurt, Germany
Copyright Elsevier

The formation of chondrules in the solar nebula is still an enigmatic process. In order to reconstruct this process, we performed a chondrule formation experiment aboard the International Space Station (ISS), called EXCISS. The purpose of the EXCISS experiment is to acquire new insights in chondrule formation by “nebular lightnings”. During the experiment forsterite (MgSiO₄) particles were repeatedly exposed to arc discharges under long-term micro-gravity conditions. The purpose of this paper is to describe the experimental set-up and establish and benchmark approaches for the analysis of the samples once they are returned from the ISS. We produced aggregates of fused MgSiO₄ particles in our Earth-based experiment which we studied by SEM and X-ray microtomography. The results of our preliminary Earth-based experiments indicate that the chosen experimental parameters will likely lead to melting of MgSiO₄ particles and the formation of aggregates. The results from the first experiments aboard the ISS revealed that the EXCISS experiment is fully operational.

¹Jeff A.Berger,²Sherry L.Cady,³Victoria E.Hamilton
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113868]
¹NASA Johnson Space Center, Houston, TX, USA
²Pacific Northwest National Laboratory, USA
³Southwest Research Institute, Boulder, CO, USA
Copyright Elsevier

Surface roughness is known to decrease thermal infrared (TIR) absorption band intensity, but studies of the effect on geologically relevant samples are relatively limited. To determine the effect of surface roughness (with features smaller than ~2/3 of the wavelength) on TIR spectra, we investigated two glass compositions with prepared roughened surfaces: (1) high purity fused silica and (2) soda-lime glass (73 wt% SiO2). We roughened the surfaces of the glasses by sandblasting and polishing with grit paper. The surfaces were characterized with scanning electron microscopy and stylus profilometry. We then analyzed the roughened glasses with TIR emittance spectroscopy. Micrometer-scale roughness causes a decrease in TIR absorption band intensity, relative to a specular surface. No significant changes in band shape or shifts in wavelength were detected. As roughness increases, empirical results show a logarithmic decrease in TIR absorption band intensity. The logarithmic trends of the two glass compositions are different; empirical roughness calibrations do not translate across different compositions. A linear, least-squares spectral deconvolution using two endmembers, specular and blackbody, predicts model spectra of roughened glass surfaces with relatively low error. This is of consequence to orbital TIR measurements of poorly constrained targets, such as the Martian surface, because micrometer-scale roughness is adequately modeled by the addition of a blackbody spectrum to the deconvolution endmember matrix.

^1,2Jessica A.Watkins,^2,3Bethany L.Ehlmann,¹An Yin
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113836]
¹Department of Earth, Planetary, and Space Sciences and Institute of Planets and Exoplanets (iPLEX), University of California, Los Angeles, CA 90095-1567, USA
²Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
³Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
Copyright Elsevier

Long-runout landslides with transport distances of >50 km are ubiquitous in Valles Marineris (VM), yet the transport mechanisms remain poorly understood. Four decades of studies reveal significant variation in landslide morphology and emplacement age, but how these variations are related to landslide transport mechanisms is not clear. In this study, we address this question by conducting systematic geological mapping and compositional analysis of VM long-runout landslides using high-resolution Mars Reconnaissance Orbiter imagery and spectral data. Our work shows that: (1) a two-zone morphological division (i.e., an inner zone characterized by rotated blocks and an outer zone expressed by a thin sheet with a nearly flat surface) characterizes all major VM landslides; (2) landslide mobility is broadly dependent on landslide mass; and (3) the maximum width of the outer zone and its transport distance are inversely related to the basal friction that was estimated from the surface slope angle of the outer zone. Our comprehensive Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) compositional analysis indicates that hydrated silicates are common in landslide outer zones and nearby trough-floor deposits. Furthermore, outer zones containing hydrated minerals are sometimes associated with longer runout and increased lateral spreading compared to those without detectable hydrated minerals. Finally, with one exception we find that hydrated minerals are absent in the inner zones of the investigated VM landslides. These results as whole suggest that hydrated minerals may have contributed to the magnitude of lateral spreading and long-distance forward transport of major VM landslides.

¹Jens Barosch,^1,2Dominik C. Hezel,³Yves Marrocchi,³Andrey Gurenko,^1,4Christoph Lenting
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13496]
¹Department of Geology and Mineralogy, University of Cologne, Zülpicher Str. 49b, 50674 Köln, Germany
²Department of Mineralogy, Natural History Museum, Cromwell Road, London, SW7 5BD UK
³CRPG, CNRS, Université de Lorraine, UMR 7358, Vandoeuvre‐lès‐Nancy, 54501 France
⁴Institute of Geoscience, University of Bonn, Meckenheimer Allee 169, 53111 Bonn, Germany
Published by arrangement with John Wiley & Sons

We found a large (~2 mm) compound object in the primitive Yamato 793408 (H3.2‐an) chondrite. It consists mostly of microcrystalline material, similar to chondrule mesostasis, that hosts an intact barred olivine (BO) chondrule. The object contains euhedral pyroxene and large individual olivine grains. Some olivine cores are indicative of refractory forsterites with very low Fe‐ and high Ca, Al‐concentrations, although no ¹⁶O enrichment. The entire object is most likely a new and unique type, as no similar compound object has been described so far. We propose that it represents an intermediate stage between compound chondrules and macrochondrules, and formed from the collision between chondrules at low velocities (below 1 m s⁻¹) at high temperatures (around 1550 °C). The macrochondrule also trapped and preserved a smaller BO chondrule. This object appears to be the first direct evidence for a genetic link between compound chondrules and macrochondrules. In accordance with previous suggestions and studies, compound chondrules and macrochondrules likely formed by the same mechanism of chondrule collisions, and each represents different formation conditions, such as ambient temperature and collision speed.

^1,2T.V.Kizovski et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.05.030]
¹Centre for Applied Planetary Mineralogy, Department of Natural History, Royal Ontario Museum, 100 Queen’s Park, Toronto, Ontario, M5S 2C6, Canada
²Department of Earth Sciences, University of Toronto, 22 Russell Street, Toronto, Ontario, M5S 3B1, Canada
Copyright Elsevier

Northwest Africa (NWA) 7042 is an intermediate, permafic shergottite consisting of two generations of olivine (early zoned olivine Fo41-76, and late-stage fayalitic olivine Fo46-56), complexly zoned pyroxene (En35-64Fs22-46Wo5-34), shock-melted or maskelynitized feldspar (An5-30Ab16-61Or1-47), and accessory merrillite, apatite, ilmenite, titanomagnetite, Fe-Cr-Ti spinels, pyrrhotite, and baddeleyite. The zoned olivine grains have been pervasively modified, containing conspicuous brown Mg-rich cores surrounded by colorless, unaltered Fe-rich overgrowth rims. This textural relationship suggests that the cores were altered at magmatic temperatures prior to crystallization of the rims on Mars. Launch-generated shock veins in NWA 7042 also crosscut and displace several of the altered olivine grains indicating that alteration occurred before ejection of the meteorite. While this type of olivine alteration is rare in shergottites, it is similar to deuterically altered olivine in basalts and gabbros on Earth, caused by residual water-rich magmatic fluids. Transmission electron microscopy analysis of the olivine alteration did not reveal the high-temperature phases expected from this process; however, NWA 7042 has also been subjected to extensive terrestrial weathering which may explain their absence. The potential presence of deuterically altered olivine in NWA 7042 has significant implications, as it is the third martian meteorite where deuteric alteration of olivine has been observed (the others being NWA 10416, and ALH 77005). The different mantle sources for the parental melts of these three meteorites would suggest many, if not all martian mantle reservoirs have the potential to produce water-rich magmas.

¹Mare, E.R.,¹O’Neill, H.S.C.,¹Berry, A.J.,²Glover, C.J.
Chemical Geology 532, 119306 Link to Article [DOI: 10.1016/j.chemgeo.2019.119306]
¹Research School of Earth Sciences, Australian National University, Canberra, ACT 2601, Australia
²Australian Synchrotron, 800 Blackburn Rd, Clayton, VIC 3168, Australia

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

¹Bahadoran, M.,^2,3Amiri, I.S.
European Physical Journal Plus 135, 205 Link to Article [DOI: 10.1140/epjp/s13360-020-00107-2]
¹Department of Physics, Shiraz University of Technology, Shiraz, Fars 31371555, Iran
²Computational Optics Research Group, Advanced Institute of Materials Science, Ton Duc Thang University, District 7, Ho Chi Minh City, 700000, Viet Nam
³Faculty of Applied Sciences, Ton Duc Thang University, District 7, Ho Chi Minh City, 700000, Viet Nam

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

¹William Abbey et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113885]
¹Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, United States of America
Copyright Elsevier

The Mars Science Laboratory (MSL) rover, Curiosity, completed its second Martian year, 1337 sols (1374 Earth days), of operation on May 11, 2016, and its third Martian year, 2006 sols (2061 Earth days), of operation on March 28, 2018. During this time the rover successfully drilled twelve full depth drill holes into the Martian surface and analyzed the recovered material using onboard instruments, giving us new insights into the potential habitability and geologic diversity of ancient Mars. During the second Martian year, four holes were drilled into the mudstones of the Murray formation: ‘Confidence Hills’ (Sol 759), ‘Mojave 2’ (Sol 882), ‘Telegraph Peak’ (908) & ‘Buckskin’ (Sol 1060); while four more holes were drilled into the sandstones of the Stimson formation: ‘Big Sky’ (Sol 1119), ‘Greenhorn’ (Sol 1137), ‘Lubango’ (Sol 1320) & ‘Okoruso’ (Sol 1332). During the third Martian year, four additional holes were drilled into the Murray formation: ‘Oudam’ (Sol 1361), ‘Marimba’ (Sol 1422), ‘Quela’ (Sol 1464) & ‘Sebina’ (Sol 1495). In this paper, we will give a brief overview of the rover sampling hardware and nominal drilling protocols, followed by a discussion of how these protocols were refined and altered early during the course of Curiosity’s second year on Mars. In addition, we will describe the ‘Bonanza King’ (Sol 724) drill campaign, the mission’s first ‘successful failure’, and how it influenced these changes. We will also briefly discuss the events leading up to the drill feed fault on Sol 1536, which resulted in suspension of all drill activities for the remainder of the third Martian year. Finally, we will present scientific highlights obtained from each drill site utilizing MSL’s onboard instrumentation (SAM & CheMin), results enabled by the drill’s ability to excavate sample at depth and transfer it to these instruments.

¹Lidia Pittarello,¹Ludovic Ferrière,¹Jean‐Guillaume Feignon,¹Gordon R. Osinski,¹Christian Koeberl
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13490]
¹Natural History Museum Vienna, Burgring 7, A‐1010 Vienna, Austria
²Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A‐1090 Vienna, Austria
Published by arrangement with John Wiley & Sons

Shocked quartz and feldspar grains commonly exhibit planar microstructures, such as planar fractures, planar deformation features, and possibly microtwins, which are considered to have formed by shock metamorphism. Their orientation and frequency are typically reported to be randomly distributed across a sample. The goal of this study is to investigate whether such microstructures are completely random within a given sample, or whether their orientation might also retain information on the direction of the local shock wave propagation. For this work, we selected samples of shatter cones, which were cut normal to the striated surface and the striation direction, from three impact structures (Keurusselkä, Finland, and Charlevoix and Manicouagan, Canada). These samples show different stages of pre‐impact tectonic deformation. Additionally, we investigated several shocked granite samples, selected at different depths along the drill core recovered during the joint IODP‐ICDP Chicxulub Expedition 364 (Mexico). In this case, thin sections were cut along two orthogonal directions, one parallel and one normal to the drill core axis. All the results refer to optical microscopy and universal‐stage analyses performed on petrographic thin sections. Our results show that such shock‐related microstructures do have a preferred orientation, but also that relating their orientation with the possible shock wave propagation is quite challenging and potentially impossible. This is largely due to the lack of dedicated experiments to provide a key to interpret the observed preferred orientation and to the lack of information on postimpact orientation modifications, especially in the case of the drill core samples.