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  • LUNAR AND PLANETARY EXPLORATION  (8)
  • 1980-1984  (8)
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Year
  • 1
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    Mechanical models of close approaches and collisions of large protoplanets (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: In models of lunar origin by great impact, attention is usually paid to the hydrodynamic expansion resulting from the great amount of thermal energy. However, the source of this disruption is inevitably significant in a close approach between large bodies, it is to be expected that significant departures from simple hyperbolic orbits would occur even before impact. These departures could arise from mechanical effects, and hence purely mechanical models are worth pursuing. The most interesting results obtained for approach offsets are small multiples of the planet radius and approach velocities of a few kilometers/second. In an interaction between Mars and Earth sized protoplanets, most of the material ends in collision, but a few percent end in elliptic orbits and a few percent escape. Another model considered is an offset collision, arising from a wide range of approach velocities and offsets.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar Planetary Inst. Conf. on the Origin of the Moon; p 59
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    NASA TECHNICAL REPORTS
  • 2
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    Tectonics and evolution of Venus (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Earlier data synthesized with data recently obtained by the Pioneer Venus Orbiter are analyzed with regard to general tectonics, interior, and long-term evolution of Venus. Comprehensive topographic maps, global properties of Venus, and variations in its gravity field are investigated, and bulk properties of Venus, earth, Mars, the sun, and chondritic meteorites relevant to planetary internal structure and evolution are studied. Although Venus was found to differ less than 30% from earth in comparing all important bulk properties, it appears to have evolved differently. It is noted that a slow rotation rate, the absence of a satellite, the virtual absence of a magnetic field, the dearth of water in the atmosphere, the abundance of primordial argon, and the high surface temperature, are properties in which Venus differs most from the earth. Further results showing the positive correlation of gravity and topography at all wavelengths and the apparent absence of any feature like an ocean indicate that Venus is a one-plate planet and its evolution apparently resembles that of Mars more than that of the earth.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 212; May 22
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  • 3
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    Heating of the moon by heterogeneous accretion (1980)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Monte Carlo models of lunar accretion are developed by randomly sampling mass and velocity distributions of objects in the solar nebula in circumsolar and circumterrestrial orbits. The thermal effect of an impact is expressed as the volume of melt produced; the melt volumes produced by each Monte Carlo case are sorted into regions to produce percentage melt estimates as a function of radius. One-hundred cases are calculated to obtain a range of plausible thermal histories for lunar accretion. The average melt percentage estimates show substantial deep melting, but the spread of melt percentage values about the mean from the random sampling procedure is wide enough to include 0% melting for radii below 100 km and 100% melting for radii below 500 km.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 85; Nov. 10
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  • 4
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    Inferences from other bodies for the earth's composition and evolution (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Properties of the earth are considered in the light of the earth's presumed status as an end member of the class of predominantly silicate solar system bodies. Bulk composition data for the inner planets are presented and processes which may account for compositional variations are discussed. Problems posed by Viking findings on Mars and Pioneer findings on Venus are mentioned. Prominent evolutionary patterns of the inner planets are discussed, including the inverse correlation of lithospheric and crustal thickness with planetary size, and the thermotectonics of Venus, Mars, and earth are compared.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 5
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    Tectonic contrasts between Venus and the earth (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The long-wave features of the gravity field of Venus differ from those of the earth's field not only in their strong positive correlation with topography, but also in their gentler spectral slope. These properties are inconsistent with generation of the gravity field by plate tectonics or by processes at great depths; they are consistent with generation by a mantle convective system supporting the broad features in topography with an effective compensation depth of about 450 km.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 11; 35-37
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  • 6
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    Implications of basaltic volcanism for the evolution of planetary bodies (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: HIG-CONTRIB-1244-VOL-2 , Hawaii Univ. Contrib. of the Hawaii Inst. of Geophys., Vol. 2; 27 p
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  • 7
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    Could plate tectonics on Venus be concealed by volcanic deposits (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The present investigation is supplementary to a study reported by Kaula and Phillips (1981). From an analysis of Pioneer Venus altimetry, Kaula and Phillips had inferred that any heat loss from the planet by plate tectonics must be small compared to that from the earth. However, it has been suggested by others that plate tectonic may exist on Venus, but that the expected 'square root of s' dependence of the topographic drop off is not observed because it is concealed by lava flows. The present investigation has the objective to conduct an examination whether this suggestion of concealment by lava flow is correct. On the basis of the performed analysis, it is concluded that the results obtained by Kaula and Phillips appear to be well justified.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters; 9; Sept
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  • 8
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    Quantitative tests for plate tectonics on Venus (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Quantitative comparisons are made between the characteristics of plate tectonics on the earth and those which are possible on Venus. Considerations of the factors influencing rise height and relating the decrease in rise height to plate velocity indicate that the rate of topographic dropoff from spreading centers should be about half that on earth due to greater rock-fluid density contrast and lower temperature differential between the surface and interior. Statistical analyses of Pioneer Venus radar altimetry data and global earth elevation data is used to identify 21,000 km of ridge on Venus and 33,000 km on earth, and reveal Venus ridges to have a less well-defined mode in crest heights and a greater concavity than earth ridges. Comparison of the Venus results with the spreading rates and associated heat flow on earth reveals plate creation rates on Venus to be 0.7 sq km/year or less and indicates that not more than 15% of Venus's energy is delivered to the surface by plate tectonics, in contrast to values of 2.9 sq km a year and 70% for earth.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters; 8; Dec. 198
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