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  • 1
    Publication Date: 2011-08-24
    Description: The first 18 tracks of laser altimeter data across the northern hemisphere of Mars from the Mars Global Surveyor spacecraft show that the planet at latitudes north of 50 degrees is exceptionally flat; slopes and surface roughness increase toward the equator. The polar layered terrain appears to be a thick ice-rich formation with a non-equilibrium planform indicative of ablation near the periphery. Slope relations suggest that the northern Tharsis province was uplifted in the past. A profile across Ares Vallis channel suggests that the discharge through the channel was much greater than previously estimated. The martian atmosphere shows significant 1-micrometer atmospheric opacities, particularly in low-lying areas such as Valles Marineris.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Science (ISSN 0036-8075); Volume 279; 5357; 1686-92
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  • 2
    Publication Date: 2011-08-24
    Description: The primary objective of the Mars Observer laser altimeter (MOLA) investigation is to determine globally the topography of Mars at a level suitable for addressing problems in geology and geophysics. Secondary objectives are to characterize the 1064-nm wavelength surface reflectivity of Mars to contribute to analyses of global surface mineralogy and seasonal albedo changes, to assist in addressing problems in atmospheric circulation, and to provide geodetic control and topographic context for the assessment of possible future Mars landing sites. The principal components of MOLA are a diode-pumped, neodymium-doped yttrium aluminum garnet laser transmitter that emits 1064-nm wavelength laser pulses, a 0.5-m-diameter telescope, a silicon avalanche photodiode detector, and a time interval unit with 10-ns resolution. MOLA will provide measurements of the topography of Mars within approximately 160-m footprints and a center-to-center along-track foot print spacing of 300 m along the Mars Observer subspacecraft ground track. The elevation measurements will be quantized with 1.5 m vertical resolution before correction for orbit- and pointing induced errors. MOLA profiles will be assembled into a global 0.2 deg x 0.2 deg grid that will be referenced to Mars' center of mass with an absolute accuracy of approximately 30 m. Other data products will include a global grid of topographic gradients, corrected individual profiles, and a global 0.2 deg x 0.2 deg grid of 1064-nm surface reflectivity.
    Keywords: ASTRONAUTICS (GENERAL)
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; E5, M; 7781-779
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  • 3
    Publication Date: 2006-04-06
    Description: A tectonic orgin for Venus banded terrain is consistent with band spacing. Both compressional (folding) and extensional models for band formation can fit present observations. Band spacing cannot distinguish among scenarios for global heat loss and for the origin of highland terrain. Tectonic models for band formation indicate that the surface brittle layer in the venus highlands is no more than a few kilometers thick.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA. Washington Repts. of Planetary Geol. Program; p 74-75
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  • 4
    Publication Date: 2006-04-06
    Description: In this paper the tectonic features of the Elysium region are identified and characterized. Identification of features was made using USGS controlled photomosaics (Elysium quadrangle, and portions of Amenthes and Cebrenia quadrangles); Viking Orbiter photographic data were used in individual cases to assist in identification. The positions and orientations of tectonic features can then be used, in conjunction with estimates of the mass of the volcanic load obtained from gravity modelling, to constrain the thickness of the elastic lithosphere in the region.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA. Washington Rept. of Planetary Geology Program, 1983; p 291-292
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  • 5
    Publication Date: 2011-08-24
    Description: Elevations from the Mars Orbiter Laser Altimeter (MOLA) have been used to construct a precise topographic map of the martian north polar region. The northern ice cap has a maximum elevation of 3 kilometers above its surroundings but lies within a 5-kilometer-deep hemispheric depression that is contiguous with the area into which most outflow channels emptied. Polar cap topography displays evidence of modification by ablation, flow, and wind and is consistent with a primarily H2O composition. Correlation of topography with images suggests that the cap was more spatially extensive in the past. The cap volume of 1.2 x 10(6) to 1.7 x 10(6) cubic kilometers is about half that of the Greenland ice cap. Clouds observed over the polar cap are likely composed of CO2 that condensed out of the atmosphere during northern hemisphere winter. Many clouds exhibit dynamical structure likely caused by the interaction of propagating wave fronts with surface topography.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Science (ISSN 0036-8075); Volume 282; 5396; 2053-60
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  • 6
    Publication Date: 2011-08-24
    Description: Elevations measured by the Mars Orbiter Laser Altimeter have yielded a high-accuracy global map of the topography of Mars. Dominant features include the low northern hemisphere, the Tharsis province, and the Hellas impact basin. The northern hemisphere depression is primarily a long-wavelength effect that has been shaped by an internal mechanism. The topography of Tharsis consists of two broad rises. Material excavated from Hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary. The present topography has three major drainage centers, with the northern lowlands being the largest. The two polar cap volumes yield an upper limit of the present surface water inventory of 3.2 to 4.7 million cubic kilometers.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Science (ISSN 0036-8075); Volume 284; 5419; 1495-503
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  • 7
    Publication Date: 2011-08-19
    Description: The evolution of a planetary atmosphere can be powerfully influenced by the planetary interior's function as both a source and a sink of atmospheric constituents; the interior can in turn be strongly influenced by the atmosphere because the mechanism of interior heat loss depends on a volatile content for which the atmosphere can serve both as sink and source. The dependence of mantle rheology on volatile content could furnish a feedback mechanism tending to keep regassing/degassing in balance, thereby maintaining a relatively constant atmospheric mass. Consideration of the abundances of radiogenic and nonradiogenic noble gases in the earth's atmosphere, and of the fluxes of these gases from the mantle, support a large degassing event early on, followed by a decrease in degassing efficiency with time and relatively inefficient outgassing over most of geologic time.
    Keywords: ASTROPHYSICS
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  • 8
    Publication Date: 2011-08-18
    Description: Comparisons of earth and Venus topography by use of Pioneer/Venus radar altimetry are examined. Approximately 93% of the Venus surface has been mapped with a horizontal resolution of 200 km and a vertical resolution of 200 m. Tectonic troughs have been indicated in plains regions which cover 65% of Venus, and hypsometric comparisons between the two planets' elevation distributions revealed that while the earth has a bimodal height distribution, Venus displays a unimodal configuration, with 60% of the planet surface within 500 m of the modal planet radius. The effects of mapping the earth at the same resolution as the Venus observations were explored. Continents and oceans were apparent, and although folded mountains appeared as high spots, no indications of tectonic activity were discernible. A NASA Venus Orbiting Imaging radar is outlined, which is designed to detect volcanoes, folded mountain ranges, craters, and faults, and thereby allow definition of possible plate-tectonic activity on Venus.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: American Scientist; 69; Nov
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  • 9
    Publication Date: 2013-08-31
    Description: Observations from approximately one-half of the Magellan nominal eight-month mission to map Venus are summarized. Preliminary compilation of initial geologic observations of the planet reveals a surface dominated by plains that are characterized by extensive and intensive volcanism and tectonic deformation. Four broad categories of units have been identified: plains units, linear belts, surficial units, and terrain units.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., 22nd Lunar and Planetary Science Conference; p 57-58
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  • 10
    Publication Date: 2016-06-07
    Description: The formation and distribution of major tectonic features on Venus are closely linked to the dominant mechanism of lithospheric heat loss. Among the most spectacular and extensive of the major tectonic features on Venus are the Chasmata, deep linear valleys generally interpreted to be the products of lithospheric extension and rifting. Systems of chasmata and related features can be traced along several tectonic zones up to 20,000 km in linear extent. Mechanical and thermal models for terrestrial continental-rifting are applied to the rift systems of Venus. The models are tested against known topographic and tectonic characteristics of Venus chasmata as well as independent information on the physical properties of the Venus crust and lithosphere.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst. Papers Presented to the Conference on Heat and Detachment in Crustal Extension on Continents and Planets; p 138 - 141
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