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  • LUNAR AND PLANETARY EXPLORATION  (15)
  • Humans
  • Lunar and Planetary Science and Exploration
  • 1975-1979  (15)
  • 1
    Publication Date: 2011-08-16
    Description: The polarization of reflected sunlight is computed for model atmospheres of Venus as a function of location on the apparent planetary disk. The calculations are for both homogeneous and layered models, as required to investigate the vertical distribution of particles. The results are compared with available observations. It is shown that the Rayleigh scattering observed in the polarization of Venus originates primarily from within the visible clouds, rather than from above the clouds. The visible 'clouds' are actually a very diffuse hazy region, and this visible-cloud layer extends at least up to the level where the pressure is of the order of 10 mb. The results indicate that the atmosphere behaves more nearly as the so-called 'homogeneous model' than as the 'reflecting-layer model'. However, there is some indication in the data that the turbidity increases with depth into the atmosphere. This conclusion receives stronger support from a comparison of particle number densities obtained from the polarization data with the number densities obtained from other observations which refer on the average to higher and lower levels in the atmosphere.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of the Atmospheric Sciences; 32; June 197
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  • 2
    Publication Date: 2011-08-17
    Description: The current state of knowledge of the Venusian clouds is reviewed. The visible clouds of Venus are shown to be quite similar to low level terrestrial hazes of strong anthropogenic influence. Possible nucleation and particle growth mechanisms are presented. The Pioneer Venus experiments that emphasize cloud measurements are described and their expected findings are discussed in detail. The results of these experiments should define the cloud particle composition, microphysics, thermal and radiative heat budget, rough dynamical features and horizontal and vertical variations in these and other parameters. This information should be sufficient to initialize cloud models which can be used to explain the cloud formation, decay, and particle life cycle.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Space Science Reviews; 20; May 1977
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  • 3
    Publication Date: 2011-08-17
    Description: With the possible exception of the lowest one or two scale heights, the dominant mode of circulation of Venus' atmosphere is a rapid, zonal, retrograde motion. Global albedo variations in the ultraviolet may reflect planetary scale waves propagating relative to the zonal winds. Other special phenomena such as cellular convection in the subsolar region and internal gravity waves generated in the interaction of the zonal circulation with the subsolar disturbance may also be revealed in ultraviolet imagery of the atmosphere. We discuss the contributions of experiments on the Orbiter and Entry Probes of Pioneer Venus toward unravelling the mystery of the planet's global circulation and the role played by waves, instabilities and convection therein
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Space Science Reviews; 20; June 197
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  • 4
    Publication Date: 2011-08-16
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 27; Apr. 197
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  • 5
    Publication Date: 2011-08-17
    Description: A general purpose filter photometer/polarimeter capable of measuring the intensity and linear polarization of scattered light at eight wavelengths in the 2350-7500 A spectral region has been adopted for the Voyager mission photopolarimeter experiment. Objectives of the experiment include determination of the vertical atmospheric aerosol distributions for Jupiter, Saturn and Titan, definition of cloud micro- and macro-structures, and identification of any regular crystalline particles in the clouds. In addition, the density of the satellite atmospheres will be assessed, and the sodium vapor distributions near Io and in the Jovian magnetosphere will be mapped. Particle size and optical depth of Saturn's rings will also be investigated.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Space Science Reviews; 21; Nov. 197
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  • 6
    Publication Date: 2011-08-17
    Description: The invariant imbedding method considered is based on an equation which describes the change in the reflected radiation when an optically thin layer is added to the top of the atmosphere. The equation is used to treat the problem of reflection from a planetary atmosphere as an initial value problem. A fast method is discussed for the solution of the invariant imbedding equation. The speed and accuracy of the new method are illustrated by comparing it with the doubling program published by Hansen and Travis (1974). Computations are performed of the equivalent widths of carbon dioxide absorption lines in solar radiation reflected by Venus for several models of the planetary atmosphere.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal; vol. 216
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  • 7
    Publication Date: 2011-08-17
    Description: Preliminary analyses of the eight volcanic eruption plumes detected on Io by Voyager 1 are presented. Plumes were observed on the bright and dark limbs of the satellite corresponding to half of the surface and range from 10,000 to 75 km in width and 280 to 70 km in height. Most plumes were observed to be umbrella-shaped, however one consists of a very diffuse cloud lacking columnar fountain characteristics. Plume sources are characterized by a dark central area, surrounded by a bright ring, which in turn is surrounded by a broad, diffuse region; the presence of similar markings in regions not observed at the limb indicates additional volcanic activity on Io. No changes were detected in the sizes or intensities of the eruptions over the 6.5-day viewing period, however a change in the appearance of a region near one plume suggests a short-lived eruption between observations. Seven of the eight plumes are located within 30 deg of the equator, implying that equatorial surfaces are generally younger than those in the polar regions.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 280; Aug. 30
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  • 8
    Publication Date: 2011-08-17
    Description: The spectrum of sunlight reflected by Jupiter is analyzed by comparing observations of Woodman (1979) with multiple-scattering computations. The analysis yields information on the vertical cloud structure at several latitudes and on the abundance of CH4 and NH3 in the atmosphere of Jupiter. The abundances of CH4 and NH3 suggest that all ices and rocks are overabundant on Jupiter by a factor of 2 or more, providing an important constraint on models for the formation of Jupiter from the primitive solar nebula. The pressure level of the clouds, the gaseous NH3 abundance, the mean temperature profile, and the Clausius-Clapeyron relation suggest that these clouds are predominantly ammonia crystals with the cloud bottom at 600-700 mb. A diffuse distribution of aerosols exists between 150 and 500 mb, and the spectral variation of albedo reflects a changing bulk absorption coefficient of the material composing the aerosols and is diagnostic of the aerosol composition.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of the Atmospheric Sciences; 36; July 197
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  • 9
    Publication Date: 2019-06-27
    Description: Polarization measurements by the orbiter cloud photopolarimeter indicate the presence of a planet-wide layer of submicrometer aerosols of substantial visible optical thickness, of the order of 0.05 to 0.01, in the lower stratosphere well above the main visible sulfuric acid cloud layer. Cloud pattern characteristics found by Mariner 10 and by Pioneer are compared. Planetary scale markings, polar region clouds, and cellular features are considered.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 203; Feb. 23
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  • 10
    Publication Date: 2019-06-27
    Description: Ultraviolet images of Venus obtained over a 3-month period show marked evolution of the planetary-scale features in the cloud patterns. The dark horizontal 'Y' feature recurs quasi-periodically at intervals of about 4 days, but has also been absent for periods of several weeks. Bow-shaped features observed in Pioneer Venus images are farther upstream from the subsolar point than those in Mariner 10 images
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 205; July 6
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