Publications (90)1079.2 Total impact
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Dataset: Overview
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Article: Ancient impact and aqueous processes at Endeavour Crater, Mars.
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ABSTRACT: The rover Opportunity has investigated the rim of Endeavour Crater, a large ancient impact crater on Mars. Basaltic breccias produced by the impact form the rim deposits, with stratigraphy similar to that observed at similar-sized craters on Earth. Highly localized zinc enrichments in some breccia materials suggest hydrothermal alteration of rim deposits. Gypsum-rich veins cut sedimentary rocks adjacent to the crater rim. The gypsum was precipitated from low-temperature aqueous fluids flowing upward from the ancient materials of the rim, leading temporarily to potentially habitable conditions and providing some of the waters involved in formation of the ubiquitous sulfate-rich sandstones of the Meridiani region.Science 05/2012; 336(6081):570-6. · 31.20 Impact Factor -
Article: Mars Exploration Rover Geologic traverse by the Spirit Rover in the Plains of Gusev Cater, Mars
Geology. 01/2010; 33:809-812. -
Article: Spirit Mars Rover Mission: Overview and selected results from the northern Home Plate Winter Haven to the side of Scamander crater
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ABSTRACT: 1] This paper summarizes Spirit Rover operations in the Columbia Hills, Gusev crater, from sol 1410 (start of the third winter campaign) to sol 2169 (when extrication attempts from Troy stopped to winterize the vehicle) and provides an overview of key scientific results. The third winter campaign took advantage of parking on the northern slope of Home Plate to tilt the vehicle to track the sun and thus survive the winter season. With the onset of the spring season, Spirit began circumnavigating Home Plate on the way to volcanic constructs located to the south. Silica‐rich nodular rocks were discovered in the valley to the north of Home Plate. The inoperative right front wheel drive actuator made climbing soil‐covered slopes problematical and led to high slip conditions and extensive excavation of subsurface soils. This situation led to embedding of Spirit on the side of a shallow, 8 m wide crater in Troy, located in the valley to the west of Home Plate. Examination of the materials exposed during embedding showed that Spirit broke through a thin sulfate‐rich soil crust and became embedded in an underlying mix of sulfate and basaltic sands. The nature of the crust is consistent with dissolution and precipitation in the presence of soil water within a few centimeters of the surface. The observation that sulfate‐rich deposits in Troy and elsewhere in the Columbia Hills are just beneath the surface implies that these processes have operated on a continuing basis on Mars as landforms have been shaped by erosion and deposition.Journal of Geophysical Research 01/2010; 115. · 3.02 Impact Factor -
Article: Exploration of Victoria crater by the Mars rover Opportunity.
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ABSTRACT: The Mars rover Opportunity has explored Victoria crater, an approximately 750-meter eroded impact crater formed in sulfate-rich sedimentary rocks. Impact-related stratigraphy is preserved in the crater walls, and meteoritic debris is present near the crater rim. The size of hematite-rich concretions decreases up-section, documenting variation in the intensity of groundwater processes. Layering in the crater walls preserves evidence of ancient wind-blown dunes. Compositional variations with depth mimic those approximately 6 kilometers to the north and demonstrate that water-induced alteration at Meridiani Planum was regional in scope.Science 06/2009; 324(5930):1058-61. · 31.20 Impact Factor -
Article: High-Silica Rocks and Soils at Gusev Crater, Mars: Distribution, Spectra, and Implications for Past Hydrothermal Activity
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ABSTRACT: The Mars Exploration Rover (MER) Spirit has discovered surprisingly high concentrations of amorphous silica in the Inner Basin of the Columbia Hills. As described by Squyres et al. (2008, Science, 320, 1063), within a topographic lowland called Eastern Valley, Spirit's Alpha Particle X-Ray Spectrometer (APXS) measured a composition of >90 wt.% silica at the soil feature "Gertrude Weise", a record high for Mars. The Mössbauer spectrum of this target is featureless. APXS measurements of light-toned nodular outcrops also show high silica concentrations (up to ~72 wt.%), which in some locations co-exist with sulfur-rich soils. Miniature Thermal Emission Spectrometer (Mini-TES) results from the soils and nodules are consistent with opal-A. These deposits have been found adjacent to "Home Plate", a layered plateau interpreted as the product of explosive volcanism. The silica-rich soils and nodules are consistent with sinters and/or residues formed in a hydrothermal system, and may be related to the same hydrovolcanic activity that produced Home Plate. We have begun to map the distribution of high-silica materials in Gusev Crater more extensively using remote sensing, in order to understand the regional extent of possible hydrothermal activity. Spirit's Pancam instrument has collected visible to near-infrared relative reflectance spectra of the region in 11 unique wavelengths. We find that a distinct absorption feature at the longest Pancam wavelength (1009 nm) appears to be characteristic of the high-silica soils and nodules. By mapping the occurrence of this feature with other spectral parameters in Pancam images, we can remotely identify potential amorphous silica deposits elsewhere in the Columbia Hills. Here we present a map with our proposed regional distribution of silica-rich materials within the rover's Gusev Crater traverse area. The mineralogic origin of the 1009nm feature is enigmatic; reflectance spectra of amorphous silica are typically featureless in near-infrared wavelengths (as are spectra of TiO2, which was also detected by the MER team in APXS data of the Gusev high-silica soils). For comparison, we have performed laboratory analyses of silica sinters and residues from hydrothermal sites at Wairakei, New Zealand and Geysir, Iceland. Based on spectral mixing models with these and other mineral spectra from digital spectral libraries, we hypothesize that the presence of water or OH, either free (trapped in pore spaces) or bound in a mineral structure (perhaps from a minor species produced together with the high-silica materials), is responsible for the spectral feature observed by Pancam.AGU Fall Meeting Abstracts. 11/2008; -1:1437. -
Article: Detection of silica-rich deposits on Mars.
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ABSTRACT: Mineral deposits on the martian surface can elucidate ancient environmental conditions on the planet. Opaline silica deposits (as much as 91 weight percent SiO2) have been found in association with volcanic materials by the Mars rover Spirit. The deposits are present both as light-toned soils and as bedrock. We interpret these materials to have formed under hydrothermal conditions and therefore to be strong indicators of a former aqueous environment. This discovery is important for understanding the past habitability of Mars because hydrothermal environments on Earth support thriving microbial ecosystems.Science 06/2008; 320(5879):1063-7. · 31.20 Impact Factor -
Article: Surface albedo observations at Gusev Crater and Meridiani Planum, Mars
Journal of Geophysical Research (Planets). 05/2008; 113(E12):6. -
Article: Spectral Stratigraphy of Victoria Crater, Meridiani Planum, Mars
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ABSTRACT: A set of consistent spectrostratigraphic units have been observed within the rim of Victoria Crater by Opportunity's Pancam. Spectral and textural characteristics of these units are described and placed in a geologic context.LPI Contributions. 06/2007; 1353:3250. -
Article: Two years at Meridiani Planum: results from the Opportunity Rover.
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ABSTRACT: The Mars Exploration Rover Opportunity has spent more than 2 years exploring Meridiani Planum, traveling approximately 8 kilometers and detecting features that reveal ancient environmental conditions. These include well-developed festoon (trough) cross-lamination formed in flowing liquid water, strata with smaller and more abundant hematite-rich concretions than those seen previously, possible relict "hopper crystals" that might reflect the formation of halite, thick weathering rinds on rock surfaces, resistant fracture fills, and networks of polygonal fractures likely caused by dehydration of sulfate salts. Chemical variations with depth show that the siliciclastic fraction of outcrop rock has undergone substantial chemical alteration from a precursor basaltic composition. Observations from microscopic to orbital scales indicate that ancient Meridiani once had abundant acidic groundwater, arid and oxidizing surface conditions, and occasional liquid flow on the surface.Science 10/2006; 313(5792):1403-7. · 31.20 Impact Factor -
Article: Planetary science: bedrock formation at Meridiani Planum.
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ABSTRACT: The Mars Exploration Rover Opportunity discovered sulphate-rich sedimentary rocks at Meridiani Planum on Mars, which are interpreted by McCollom and Hynek as altered volcanic rocks. However, their conclusions are derived from an incorrect representation of our depositional model, which is upheld by more recent Rover data. We contend that all the available data still support an aeolian and aqueous sedimentary origin for Meridiani bedrock.Nature 10/2006; 443(7107):E1-2; discussion E2. · 36.28 Impact Factor -
Article: Overview of the Microscopic Imager Investigation during Spirit's first 450 sols in Gusev crater
Journal of Geophysical Research 02/2006; 111:2. · 3.02 Impact Factor -
Article: Overview of the Spirit Mars Exploration Rover Mission to Gusev Crater: Landing site to Backstay Rock in the Columbia Hills
Journal of Geophysical Research 01/2006; · 3.02 Impact Factor -
Article: Overview of the Opportunity Mars Exploration Rover mission to Meridiani Planum: Eagle crater to Purgatory ripple
Journal of Geophysical Research 01/2006; · 3.02 Impact Factor -
Article: Overview of the Spirit Mars Exploration Rover Mission to Gusev Crater: Landing site to Backstay Rock in the Columbia Hills
Journal of Geophysical Research 01/2006; · 3.02 Impact Factor -
Article: Overview of the Opportunity Mars Exploration Rover mission to Meridiani Planum: Eagle crater to Purgatory ripple
Journal of Geophysical Research 01/2006; 111. · 3.02 Impact Factor -
Article: Characterization and petrologic interpretation of olivine-rich basalts at Gusev Crater, Mars
Journal of Geophysical Research 01/2006; 111. · 3.02 Impact Factor -
Article: Geology of the Gusec cratered plains from the Spirit rover transverse
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ABSTRACT: 1] The cratered plains of Gusev traversed by Spirit are generally low-relief rocky plains dominated by impact and eolian processes. Ubiquitous shallow, soil-filled, circular depressions, called hollows, are modified impact craters. Rocks are dark, fine-grained basalts, and the upper 10 m of the cratered plains appears to be an impact-generated regolith developed over intact basalt flows. Systematic field observations across the cratered plains identified vesicular clasts and rare scoria similar to original lava flow tops, consistent with an upper inflated surface of lava flows with adjacent collapse depressions. Crater and hollow morphometry are consistent with most being secondaries. The size-frequency distribution of rocks >0.1 m diameter generally follows exponential functions similar to other landing sites for total rock abundances of 5–35%. Systematic clast counts show that areas with higher rock abundance and more large rocks have higher thermal inertia. Plains with lower thermal inertia have fewer rocks and substantially more pebbles that are well sorted and evenly spaced, similar to a desert pavement or lag. Eolian bed forms (ripples and wind tails) have coarse surface lags, and many are dust covered and thus likely inactive. Deflation of the surface $5–25 cm likely exposed two-toned rocks and elevated ventifacts and transported fines into craters creating the hollows. This observed redistribution yields extremely slow average erosion rates of $0.03 nm/yr and argues for very little long-term net change of the surface and a dry and desiccating environment similar to today's since the Hesperian (or $3 Ga).Journal of Geophysical Research 01/2006; 111:2-7. · 3.02 Impact Factor -
Article: THEMIS-VIS Measurements of the Altitude and Velocity of Clouds in the Martian Mesosphere
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ABSTRACT: Although Mars Odyssey's Thermal Emission Imaging System visible subsystem (THEMIS-VIS) was not designed or intended for stereo imaging or cloud tracking, its multiple exposure color-imaging sequence serendipitously causes a parallax effect that allows the height of high-altitude clouds to be determined, and has sufficient time delay to detect the movement of these clouds. As a result, THEMIS-VIS has acquired exceptionally high resolution (36 or 72 m pixel scale) nadir-pointed images of martian clouds with altitudes in the 60-80 km altitude range, and is providing the first direct measurements of wind speed at these altitudes. We discover high altitude cloud candidates by noticing a severe misalignment of cloud features between any two bands of an image which has been map-projected at the altitude of the local surface. In order to measure altitude and velocity, we reproject the subframes that make up a THEMIS-VIS image at a series altitudes above the local surface, shifting the subframes relative to each other to account for a range of candidate velocities. To select the best fitting altitude and velocity, we manually inspect the reprojected images to find an approximate solution, and then maximize the correlation between the 425 nm band and 540 nm band within a manually selected high-constrast cloud-dominated region of the image in order to refine the solution. The precision of this technique is of course inherently limited by the sharpness of the cloud features. To date we have obtained two high-altitude velocity measurements, and have identified 50 more images with high altitude clouds that are likely to yield velocity measurements. In THEMIS sequence number V06930045, 217 degrees L_s and 47 degrees north latitude, we measure eastward cloud motion of 60 +/- 15 m/s at an altitude of 70 +/- 5 km. In THEMIS sequence number V10526009, 26 degrees L_s and 0.5 degrees north latitude, we measure westward cloud motion of 90 +/- 20 m/s at an altitude of 80 +/- 5 km.AGU Fall Meeting Abstracts. 11/2005; -1:03. -
Article: Aeolian processes at the Mars Exploration Rover Meridiani Planum landing site.
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ABSTRACT: The martian surface is a natural laboratory for testing our understanding of the physics of aeolian (wind-related) processes in an environment different from that of Earth. Martian surface markings and atmospheric opacity are time-variable, indicating that fine particles at the surface are mobilized regularly by wind. Regolith (unconsolidated surface material) at the Mars Exploration Rover Opportunity's landing site has been affected greatly by wind, which has created and reoriented bedforms, sorted grains, and eroded bedrock. Aeolian features here preserve a unique record of changing wind direction and wind strength. Here we present an in situ examination of a martian bright wind streak, which provides evidence consistent with a previously proposed formational model for such features. We also show that a widely used criterion for distinguishing between aeolian saltation- and suspension-dominated grain behaviour is different on Mars, and that estimated wind friction speeds between 2 and 3 m s(-1), most recently from the northwest, are associated with recent global dust storms, providing ground truth for climate model predictions.Nature 08/2005; 436(7047):58-61. · 36.28 Impact Factor
Top co-authors
Top Journals
- Science (26)
- Journal of Geophysical Research (8)
- Nature (4)
- Science (2)
- Nature (1)
Institutions
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2005–2013
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Cornell University
- Department of Astronomy
Ithaca, NY, USA -
Texas A&M University
College Station, TX, USA -
Utah Geological Survey
Salt Lake City, UT, USA -
Jet Propulsion Laboratory
Pasadena, CA, USA
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2004–2012
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Arizona State University
- School of Earth and Space Exploration
Tempe, AZ, USA -
University of Tennessee
- Earth and Planetary Sciences
Knoxville, TN, USA
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2004–2005
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United States Geological Survey
Wellsboro, PA, USA -
Washington University in St. Louis
- Department of Earth and Planetary Sciences
Saint Louis, MO, USA
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