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  • 1
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    Estimating rock compressive strength from Rock Abrasion Tool (RAT) grinds (2013)
    Wiley
    Details
    Publication Date: 2013-02-13
    Description: [1]  Each Mars Exploration Rover carries a Rock Abrasion Tool (RAT) whose intended use was to abrade the outer surfaces of rocks to expose more pristine material. Motor currents drawn by the RAT motors are related to strength and hardness of rock surfaces undergoing abrasion, and this data can be usedto infer more about a target rock's physical properties. However, no calibration of the RAT exists. Here, we attempt to derive an empirical correlationusing an assemblage of terrestrial rocks and apply this correlationto data returned by the rover Spirit. The results demonstrate a positive correlation between rock strength and RAT grind energy for rocks with compressive strengths less than about 150 MPa, a category that includes all but the strongest intact rocks. Applying this correlationto rocks abraded by Spirit's RAT, the results indicate a large divide in strength between more competent basaltic rocks encountered in the plains of Gusev crater (Adirondack Class rocks) and the weaker variety of rock types measured in the Columbia Hills. Adirondack Class rocks have estimated compressive strengths in the range of 110-160 MPa and are significantly less strong than fresh terrestrial basalts; this may be indicative of a degree of weathering-induced weakening. Rock types in the Columbia Hills (Wishstone, Watchtower, Clovis, and Peace class) all have compressive strengths 〈 50 MPa and are consistent with impactites or volcanoclastic materials.In general, when considered alongside chemical, spectral, and rock textural data, these inferred compressive strength results help inform our understanding of rock origins and modification history.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Higher-than-predicted saltation threshold wind speeds on Titan (2014)
    Nature Publishing Group (NPG)
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    Publication Date: 2014-12-10
    Description: Titan, the largest satellite of Saturn, exhibits extensive aeolian, that is, wind-formed, dunes, features previously identified exclusively on Earth, Mars and Venus. Wind tunnel data collected under ambient and planetary-analogue conditions inform our models of aeolian processes on the terrestrial planets. However, the accuracy of these widely used formulations in predicting the threshold wind speeds required to move sand by saltation, or by short bounces, has not been tested under conditions relevant for non-terrestrial planets. Here we derive saltation threshold wind speeds under the thick-atmosphere, low-gravity and low-sediment-density conditions on Titan, using a high-pressure wind tunnel refurbished to simulate the appropriate kinematic viscosity for the near-surface atmosphere of Titan. The experimentally derived saltation threshold wind speeds are higher than those predicted by models based on terrestrial-analogue experiments, indicating the limitations of these models for such extreme conditions. The models can be reconciled with the experimental results by inclusion of the extremely low ratio of particle density to fluid density on Titan. Whereas the density ratio term enables accurate modelling of aeolian entrainment in thick atmospheres, such as those inferred for some extrasolar planets, our results also indicate that for environments with high density ratios, such as in jets on icy satellites or in tenuous atmospheres or exospheres, the correction for low-density-ratio conditions is not required.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Burr, Devon M -- Bridges, Nathan T -- Marshall, John R -- Smith, James K -- White, Bruce R -- Emery, Joshua P -- England -- Nature. 2015 Jan 1;517(7532):60-3. doi: 10.1038/nature14088. Epub 2014 Dec 8.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Earth and Planetary Sciences Department, University of Tennessee-Knoxville, 306 EPS Building, 1412 Circle Drive, Knoxville, Tennessee 37996, USA. ; Space Department, Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland 20723, USA. ; SETI Institute, 189 Bernardo Avenue, Suite 100, Mountain View, California 94043, USA. ; Arizona State University, Tempe, Arizona 85287-1404, USA. ; Department of Mechanical Engineering, University of California Davis, California 95616, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25487154" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 3
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    Results from the Mars Pathfinder camera (1997)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 1997
    Description: Images of the martian surface returned by the Imager for Mars Pathfinder (IMP) show a complex surface of ridges and troughs covered by rocks that have been transported and modified by fluvial, aeolian, and impact processes. Analysis of the spectral signatures in the scene (at 440- to 1000-nanometer wavelength) reveal three types of rock and four classes of soil. Upward-looking IMP images of the predawn sky show thin, bluish clouds that probably represent water ice forming on local atmospheric haze (opacity approximately 0.5). Haze particles are about 1 micrometer in radius and the water vapor column abundance is about 10 precipitable micrometers.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Smith, P H -- Bell, J F 3rd -- Bridges, N T -- Britt, D T -- Gaddis, L -- Greeley, R -- Keller, H U -- Herkenhoff, K E -- Jaumann, R -- Johnson, J R -- Kirk, R L -- Lemmon, M -- Maki, J N -- Malin, M C -- Murchie, S L -- Oberst, J -- Parker, T J -- Reid, R J -- Sablotny, R -- Soderblom, L A -- Stoker, C -- Sullivan, R -- Thomas, N -- Tomasko, M G -- Wegryn, E -- New York, N.Y. -- Science. 1997 Dec 5;278(5344):1758-65.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA. psmith@lpl.arizona.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9388170" target="_blank"〉PubMed〈/a〉
    Keywords: Atmosphere ; *Extraterrestrial Environment ; Ice ; *Mars ; Minerals ; *Water ; Wind
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    Earth-like sand fluxes on Mars (2012)
    Nature Publishing Group (NPG)
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    Publication Date: 2012-05-19
    Description: Strong and sustained winds on Mars have been considered rare, on the basis of surface meteorology measurements and global circulation models, raising the question of whether the abundant dunes and evidence for wind erosion seen on the planet are a current process. Recent studies showed sand activity, but could not determine whether entire dunes were moving--implying large sand fluxes--or whether more localized and surficial changes had occurred. Here we present measurements of the migration rate of sand ripples and dune lee fronts at the Nili Patera dune field. We show that the dunes are near steady state, with their entire volumes composed of mobile sand. The dunes have unexpectedly high sand fluxes, similar, for example, to those in Victoria Valley, Antarctica, implying that rates of landscape modification on Mars and Earth are similar.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Bridges, N T -- Ayoub, F -- Avouac, J-P -- Leprince, S -- Lucas, A -- Mattson, S -- England -- Nature. 2012 May 9;485(7398):339-42. doi: 10.1038/nature11022.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Space Department, Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland 20723, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22596156" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 5
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    A closer look at water-related geologic activity on Mars (2007)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2007-09-22
    Description: Water has supposedly marked the surface of Mars and produced characteristic landforms. To understand the history of water on Mars, we take a close look at key locations with the High-Resolution Imaging Science Experiment on board the Mars Reconnaissance Orbiter, reaching fine spatial scales of 25 to 32 centimeters per pixel. Boulders ranging up to approximately 2 meters in diameter are ubiquitous in the middle to high latitudes, which include deposits previously interpreted as finegrained ocean sediments or dusty snow. Bright gully deposits identify six locations with very recent activity, but these lie on steep (20 degrees to 35 degrees) slopes where dry mass wasting could occur. Thus, we cannot confirm the reality of ancient oceans or water in active gullies but do see evidence of fluvial modification of geologically recent mid-latitude gullies and equatorial impact craters.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉McEwen, A S -- Hansen, C J -- Delamere, W A -- Eliason, E M -- Herkenhoff, K E -- Keszthelyi, L -- Gulick, V C -- Kirk, R L -- Mellon, M T -- Grant, J A -- Thomas, N -- Weitz, C M -- Squyres, S W -- Bridges, N T -- Murchie, S L -- Seelos, F -- Seelos, K -- Okubo, C H -- Milazzo, M P -- Tornabene, L L -- Jaeger, W L -- Byrne, S -- Russell, P S -- Griffes, J L -- Martinez-Alonso, S -- Davatzes, A -- Chuang, F C -- Thomson, B J -- Fishbaugh, K E -- Dundas, C M -- Kolb, K J -- Banks, M E -- Wray, J J -- New York, N.Y. -- Science. 2007 Sep 21;317(5845):1706-9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA. mcewen@lpl.arizona.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17885125" target="_blank"〉PubMed〈/a〉
    Keywords: Extraterrestrial Environment ; Geological Phenomena ; Geology ; *Mars ; *Water
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 6
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    Seasonal erosion and restoration of Mars' northern polar dunes (2011)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2011-02-05
    Description: Despite radically different environmental conditions, terrestrial and martian dunes bear a strong resemblance, indicating that the basic processes of saltation and grainfall (sand avalanching down the dune slipface) operate on both worlds. Here, we show that martian dunes are subject to an additional modification process not found on Earth: springtime sublimation of Mars' CO(2) seasonal polar caps. Numerous dunes in Mars' north polar region have experienced morphological changes within a Mars year, detected in images acquired by the High-Resolution Imaging Science Experiment on the Mars Reconnaissance Orbiter. Dunes show new alcoves, gullies, and dune apron extension. This is followed by remobilization of the fresh deposits by the wind, forming ripples and erasing gullies. The widespread nature of these rapid changes, and the pristine appearance of most dunes in the area, implicates active sand transport in the vast polar erg in Mars' current climate.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hansen, C J -- Bourke, M -- Bridges, N T -- Byrne, S -- Colon, C -- Diniega, S -- Dundas, C -- Herkenhoff, K -- McEwen, A -- Mellon, M -- Portyankina, G -- Thomas, N -- New York, N.Y. -- Science. 2011 Feb 4;331(6017):575-8. doi: 10.1126/science.1197636.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Planetary Science Institute, Tucson, AZ 85719, USA. cjhansen@psi.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21292976" target="_blank"〉PubMed〈/a〉
    Keywords: *Carbon Dioxide ; Dry Ice ; Extraterrestrial Environment ; *Mars
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 7
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    Chemistry, Mineralogy, and Grain Properties at Namib and High Dunes, Bagnold Dune Field, Gale Crater, Mars: A Synthesis of Curiosity Rover Observations (2017)
    Wiley
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    Publication Date: 2017-06-13
    Description: The Mars Science Laboratory Curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active Bagnold dune field. The Bagnold sands are rounded to subrounded, very fine- to medium- sized (~45-500 µm) with ≥6 distinct grain colors. In contrast to sands examined by Curiosity in a dust-covered, inactive bedform called Rocknest and soils at other landing sites, Bagnold sands are darker, less red, better sorted, have fewer silt-sized or smaller grains, and show no evidence for cohesion. Nevertheless, Bagnold mineralogy and Rocknest mineralogy are similar with plagioclase, olivine, and pyroxenes in similar proportions comprising 〉90% of crystalline phases, along with a substantial amorphous component (35% ± 15%). Yet, Bagnold and Rocknest bulk chemistry differ. Bagnold sands are Si-enriched relative to other soils at Gale crater, and H 2 O, S, and Cl are lower relative to all previously measured martian soils and most Gale crater rocks. Mg, Ni, Fe, and Mn are enriched in the coarse-sieved fraction of Bagnold sands, corroborated by VNIR spectra that suggest enrichment of olivine. Collectively, patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in martian soils: (1) amorphous components in the sand-sized fraction (represented by Bagnold) that are Si-enriched, hydroxylated alteration products and/or impact or volcanic glasses; and (2) amorphous components in the fine fraction (〈40 µm; represented by Rocknest and other bright soils) that are Fe-, S-, and Cl-enriched with low Si and adsorbed and structural H 2 O.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 8
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    Compositional Variations in Sands of the Bagnold Dunes, Gale Crater, Mars, from Visible-Shortwave Infrared Spectroscopy and Comparison to Ground-Truth from the Curiosity Rover (2017)
    Wiley
    Details
    Publication Date: 2017-04-15
    Description: During its ascent up Mount Sharp, the Mars Science Laboratory Curiosity rover traversed the Bagnold Dune Field. We model sand modal mineralogy and grain size at four locations near the rover traverse, using orbital shortwave infrared single scattering albedo spectra and a Markov-Chain Monte Carlo implementation of Hapke's radiative transfer theory to fully constrain uncertainties and permitted solutions. These predictions, evaluated against in situ measurements at one site from the Curiosity rover, show that XRD-measured mineralogy of the basaltic sands is within the 95% confidence interval of model predictions. However, predictions are relatively insensitive to grain size and are non-unique, especially when modeling the composition of minerals with solid solutions. We find an overall basaltic mineralogy and show subtle spatial variations in composition in and around the Bagnold dunes, consistent with a mafic enrichment of sands with cumulative transport distance by sorting of olivine, pyroxene, and plagioclase grains during aeolian saltation. Furthermore, the large variations in Fe and Mg abundances (~20 wt%) at the Bagnold Dunes suggest that compositional variability induced by wind sorting may be enhanced by local mixing with proximal sand sources. Our estimates demonstrate a method for orbital quantification of composition with rigorous uncertainty determination and provide key constraints for interpreting in situ measurements of compositional variability within martian aeolian sandstones.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 9
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    Martian Aeolian Activity at the Bagnold Dunes, Gale Crater: The View from the Surface and Orbit (2017)
    Wiley
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    Publication Date: 2017-05-31
    Description: The first in situ investigation of an active dune field on another planetary surface occurred in 2015-2016 when the MSL Curiosity rover investigated the Bagnold Dunes on Mars. HIRISE images show clear seasonal variations that are in good agreement with atmospheric model predictions of intra-annual sand flux and migration directions that together indicate that the campaign occurred during a period of low wind activity. Curiosity surface images show that limited changes nevertheless occurred, with movement of large grains, particularly on freshly exposed surfaces, two occurrences of secondary grain flow on the slip face of Namib Dune, and a slump on a freshly exposed surface of a large ripple. These changes are seen at sol-to-sol time scales. Grains on a rippled sand deposit and unconsolidated dump piles show limited movement of large grains over a few hours during which mean friction speeds are estimated at 0.3 - 0.4 m s -1 . Overall, the correlation between changes and peak REMS winds is moderate, with high wind events associated with changes in some cases, but not in others, suggesting that other factors are also at work. The distribution of REMS 1 Hz wind speeds show a tail up to the 20 m s -1 , showing that even higher speed winds occur. Non-aeolian triggering mechanisms are also possible. The low activity period at the dunes documented by Curiosity provides clues to processes that dominated in the Martian past under conditions of lower obliquity.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 10
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    “Sedimentary processes of the Bagnold Dunes: Implications for the eolian rock record of Mars” (2017)
    Wiley
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    Publication Date: 2017-07-07
    Description: The Mars Science Laboratory rover Curiosity visited two active wind-blown sand dunes within Gale crater, Mars, which provided the first ground-based opportunity to compare martian and terrestrial eolian dune sedimentary processes and study a modern analog for the martian eolian rock record. Orbital and rover images of these dunes reveal terrestrial-like and uniquely martian processes. The presence of grainfall, grainflow, and impact ripples resembled terrestrial dunes. Impact ripples were present on all dune slopes and had a size and shape similar to their terrestrial counterpart. Grainfall and grainflow occurred on dune and large ripple lee slopes. Lee slopes were ~29° where grainflows were present and ~33° where grainfall was present. These slopes are interpreted as the dynamic and static angles of repose, respectively. Grainsize measured on an undisturbed impact ripple ranges between 50 μm and 350 μm with an intermediate axis mean size of 113 μm (median: 103 μm). Dissimilar to dune eolian processes on Earth, large, meter-scale ripples were present on all dune slopes. Large ripples had nearly symmetric to strongly asymmetric topographic profiles and heights ranging between 12 cm and 28 cm. The composite observations of the modern sedimentary processes highlight that the martian eolian rock record is likely different from its terrestrial counterpart because of the large ripples, which are expected to engender a unique scale of cross-stratification. More broadly, however, in the Bagnold Dune Field as on Earth, dune-field pattern dynamics and basin-scale boundary conditions will dictate the style and distribution of sedimentary processes.
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    Topics: Geosciences , Physics
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