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  • LUNAR AND PLANETARY EXPLORATION  (13)
  • Chemistry  (9)
  • 2015-2019
  • 1985-1989  (11)
  • 1980-1984  (11)
  • 1955-1959
  • 11
    Publikationsdatum: 2013-08-31
    Beschreibung: Results are presented from a comprehensive analysis of crater size frequency distributions compiled from Viking Orbiter images of Martian south polar terrains. Depositional histories for the various terrain units are modelled based on deviations of cumulative crater size frequency plots from an assumed production function. Stratigraphic and morphologic data obtained from visual examination of Viking images are also used, primarily to corroborate inferences concerning ages and obliteration histories derived from the crater data.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1986; p 418-419
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 12
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    In:  Other Sources
    Publikationsdatum: 2019-01-25
    Beschreibung: It is shown how crater size-density counts may be used to help constrain the history of the Venus atmosphere, based on the predictions of simple but reasonable models for crater production, surface erosion, and the effects of atmospheric drag and breakup on incident meteors in the Venus atmosphere. In particular, if the atmosphere is young, the old (uneroded) surfaces will have crater densities upward of 0.0001/sq km and a ratio of small (4 km) craters to large (128 km) craters near 1000. If the atmosphere is old and the breakup mechanism is dominant, absolute crater densities on Venus surfaces will be diminished by several orders of magnitude relative to the young atmosphere case. If atmospheric drag is dominant, the absolute crater density will be lowered by perhaps an order of magnitude relative to the young atmosphere case, and the ratio of small to large craters will be reduced to a value near 10 to the 1.5 power. Once a large fraction of Venus surface has been imaged at kilometer resolution, as the Venus Orbiting Imaging Radar project promises to do, it could be possible to make an early determination of the age of the Venus atmosphere.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Lunar and Planetary Inst., Abstracts for the Venus Geoscience Tutorial and Venus Geologic Mapping Workshop; p 26
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 13
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    In:  Other Sources
    Publikationsdatum: 2019-06-28
    Beschreibung: The present investigation is concerned with the results of a study of wind direction indicators contained in the Viking and Mariner 9 data sets. It is found that wind direction measurements from a variety of indicators, taken over several Mars years at many longitudes, exhibit a high degree of consistency and seasonal reproducibility. It is, therefore, possible to interpret most of the observations in terms of the zonally symmetric circulation of Mars. When combined with models of the atmospheric circulation, observed wind directions can be used to set loose constraints on the polar cap mass fluxes and thermal fields which drive the flows. It is pointed out that polar cap formation seems to control the wind directions at mid and high latitudes in both hemispheres during autumn and early winter.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 88; 10189-10
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 14
    Publikationsdatum: 2019-06-28
    Beschreibung: The times and locations of occurrence are measured, as are the wavelengths and, when possible, the apparent velocity of motion of these clouds. The wavelengths of the patches of ripple clouds that are often found with the long formations are tabulated. The long clouds are observed only in the early morning hours, suggesting that they are associated with drainage winds caused by a cold planetary boundary layer. Simple mathematical models are developed to examine various aspects of such boundary winds; these make it possible to construct a complete and self-consistent explanation of all the observed features of the cloud formations.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research; 87; Feb. 1
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 15
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    In:  Other Sources
    Publikationsdatum: 2019-06-28
    Beschreibung: The changing sky brightness during the Martian twilight as measured by the Viking lander cameras is shown to be consistent with data obtained from sky brightness measurements. An exponential distribution of dust with a scale height of 10 km, equal to the atmospheric scale height, is consistent with the shape of the light curve. Multiple scattering resulting from the forward scattering peak of large particles makes a major contribution to the intensity of the twilight. The spectral distribution of light in the twilight sky may require slightly different optical properties for the scattering particles at high levels from those of the aerosol at lower levels.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research; 86; July 1
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 16
    facet.materialart.
    Unbekannt
    In:  Other Sources
    Publikationsdatum: 2019-06-28
    Beschreibung: At the surface, the atmosphere of Mars contains approximately 95.3 percent CO2 by volume. At the Viking Lander 1 (VL1) site, the total surface pressure varied with the season between about 6.89 and 8.94 mbar. Questions related to the observed CO2 pressure on Mars are explored. Several published estimates of the total amount of CO2 outgassed over the history of Mars, varying between 140 and 3000 mbar, are shown in a table. It is pointed out that the study of likely reservoirs for outgassed CO2 has focused mainly on the polar caps and regolith. Constraints on the formation of transitory pockets of moist soil are discussed, taking into account heat requirements, supply of water, and constraints related to pressure. Attention is also given to chemical considerations, implications for the current status of CO2 reservoirs, and scenarios for the evolution of CO2 pressure.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 62; 175-190
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 17
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    Unbekannt
    In:  Other Sources
    Publikationsdatum: 2019-06-28
    Beschreibung: It is shown how crater size-density counts may be used to help constrain the history of the Venus atmosphere, based on the predictions of simple but reasonable models for crater production, surface erosion, and the effects of atmospheric drag and breakup on incident meteors in the Venus atmosphere. In particular, if the atmosphere is young, the old (uneroded) surfaces will have crater densities upward of 0.0001/sq km and a ratio of small (4 km) craters to large (128 km) craters near 1000. If the atmosphere is old and the breakup mechanism is dominant, absolute crater densities on Venus surfaces will be diminished by several orders of magnitude relative to the young atmosphere case. If atmospheric drag is dominant, the absolute crater density will be lowered by perhaps an order of magnitude relative to the young atmosphere case, and the ratio of small to large craters will be reduced to a value near 10 to the 1.5 power. Once a large fraction of Venus surface has been imaged at kilometer resolution, as the VOIR project promises to do, it could be possible to make an early determination of the age of the Venus atmosphere.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus; 49; Jan. 198
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 18
    Publikationsdatum: 2019-06-28
    Beschreibung: All Mariner 9 and Viking Orbiter images of Martian atmospheric clouds were analyzed to obtain temporal meteorological characteristics of Mars. The data comprised over 57,000 images which were separated into seven categories of surface obscuration. The classes included: lee waves, waves, plumes, streak clouds, cloud streets, localized fogs and hazes and were associated with particular formation mechanisms, probabilities of wind shear, static stability and surface shear stress and composition. Near surface winds followed the cap edges except in summer. Hemispheric asymmetries were attributed to the hydration state and global dust storm effects. Static stability was regionally and seasonally variable. Finally, clouds formed more easily in the northern than in the southern hemisphere in all corresponding seasons.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 89; 6671-668
    Format: text
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  • 19
    Publikationsdatum: 2019-07-12
    Beschreibung: A detailed modeling of the observed crater populations in stratigraphic unit mappings of the Martian south pole region is presently used to establish absolute constraints on the age of materials' emplacement. Modeling results indicate that cratered terrains poleward of 65 deg south latitude have subsequently experienced a steady-state net accumulation of materials at about 0.1 km/Ga; equatorial cratered terrains have by contrast retained a virtually pristine form.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 76; 357-377
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 20
    Publikationsdatum: 2019-07-12
    Beschreibung: A numerical, self-consistent model is defined for filtering out the effects of haze which cause a loss of fine-scale features in Viking Orbiter imagery of the Mars surface. Increased definition is necessary if the visual data is to serve for identifying terrain features which indicate the presence of volatiles such as ice. Crater images are used to calculate the change in atmospheric optical properties that accounts for alterations in the discriminability of crater features. Modulation transfer functions are developed for the image obscuration contributions of the atmosphere and the camera lens, thereby quantifying the smallest crater (6-7 pixels) that can be seen. The radiance of the viewed scene is modeled, and an atmospheric obscuration parameter is obtained as a function of the ratio of the atmospheric and surface obscuration contributions to the radiance at the detector. The contribution of the surface alone can then be identified. The model is applied in calculations of the total number of observed craters for comparisons with the expected number of craters, and to assess the potential for using the Viking cameras to characterize the geomorphic properties of various regions of the Mars surface.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 66; 22-38
    Format: text
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