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  • LUNAR AND PLANETARY EXPLORATION  (16)
  • GEOPHYSICS  (1)
  • perturbation theory
  • 1975-1979  (17)
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Year
  • 1
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    The surface and interior of Venus (1977)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: The present knowledge of Venus is reviewed with discussions of the nature and history of both the surface, crust and interior. Instrumentation on board the Pioneer Venus Orbiter, including the radar mapper, radio tracking and the fluxgate magnetometer, is described. Topographic, geological, Bouguer gravity, magnetic, and crustal thickness maps will be constructed from Orbiter data. These maps should provide information on composition and thermal history, the major geological or geophysical provinces, the rate of past and present tectonic activity, and evidence of past or present MHD dynamos.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Space Science Reviews; 20; June 197
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Pioneer Venus radar mapper experiment (1979)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Altimetry and radar scattering data for Venus, obtained from 10 of the first 13 orbits of the Pioneer Venus orbiter, have disclosed what appears to be a rift valley having vertical relief of up to 7 kilometers, as well as a neighboring, gently rolling plain. Planetary oblateness appears unlikely to exceed 1/2500 and may be substantially smaller.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 203; Feb. 23
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  • 3
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    Venus - Preliminary topographic and surface imaging results from the Pioneer Orbiter (1979)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Three large Venus surface features, identified previously in images obtained from earth-based radar observations, are shown by the Pioneer Venus radar mapper to be elevated 5 to 10 km above the surrounding terrain. Two of these features, one bright and the other dark, lie adjacent to each other astride the 65 N parallel between longitudes 310 E and 10 E. The combined region forms a huge tectonically uplifted plateau, surmounted by radar-bright ridges that may have either a volcanic or tectonic origin. The third feature, located at 30 N, 283 E, is radar-bright and may consist of volcanic material extruded along a fault zone. A first radar-scattering image, compiled from data obtained by the mapper in its imaging mode, shows a region north of the equator; several circular depressions seen in this area may result from meteoritic impact.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 205; July 6
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    NASA TECHNICAL REPORTS
  • 4
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    Equilibrium velocities of a planetesimal population (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The random velocities of planetesimal populations specified by maximum and minimum masses and a power-law number density are calculated iteratively. The calculation is based on two different physical models involving ratios of rates: (1) excitation of kinetic energy by gravitational perturbation and elastic collision equal to damping of kinetic energy by inelastic collisions; and (2) excitation of kinetic energy a ratio b (about 3 usually) to doubling of mass. Both physical models are developed approximately and then more precisely. The approximate model (2) agrees with results of Safronov (1972). Both precise models are applied to populations approximating those generated by the calculations of Greenberg et al. (1978), Cox and Lewis (1979), and Wetherill (1979).
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 40; Nov. 197
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  • 5
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    Thermal evolution of earth and moon growing by planetesimal impacts (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Improved estimates of impact energy partitioning are combined with models of planetesimal size distribution and planetary growth to infer the early thermal evolutions of the earth and moon. Binary accretion models of the moon which allow for enhancement of velocities by proximity of the earth do not get hot enough for appreciable melting unless a planetesimal mass distribution starting at a rather high value (earth mass/20 or more) is assumed. This melting occurs deeper than is inferred from petrological and thermotectonic data; hence the results favor formation of the moon as a consequence of a great impact (or great impacts) into the earth.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 84; Mar. 10
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  • 6
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    Absolute plate motions by boundary velocity minimizations (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The main interaction of the earth's interior with the lithosphere is as a material source and sink. An absolute reference frame defined by minimizing the translational motion of tectonic plate boundaries differs by 0.6 cm/year from a frame defined by hot spot traces and by 0.4 cm/year from the frame defined by the most plausible model of drag forces on the plates. The rms absolute translational velocities are about 2 cm/year for ocean-ocean plate boundaries and 1.5 cm/year for ocean-continent plate boundaries. The close agreement between the source and sink and the drag-dependent definitions suggests that the lithosphere, as a stress guide, to some extent controls the locations of its sources and sinks.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 80; Jan. 10
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  • 7
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    The seven ages of a planet (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: On the basis of almost universally held assumptions concerning the formation of the planets and the isolation of the solar system from outside influences it follows rather plausibly that all terrestrial planets pass in principle through seven stages. The processes involved include the solidification of grains from gas in the condensation stage, planetesimal interactions, and formation processes. Vigorous convection processes lead to the gravitational separation of iron and the outgassing of oceans. Other stages are related to plate tectonics and terminal volcanism. The ultimate stage of quiescence is characterized by a thick lithosphere and no volcanism.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 26; Sept
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  • 8
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    The gravity and shape of the moon (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Current knowledge about the gravity and geometry of the moon is discussed which has been obtained by Doppler tracking of lunar orbiters, laser ranging, metric photography, and various instruments landed on the moon. Determinations of spherical harmonic coefficients of the lunar gravitational field are described, significant features observed in the field are noted (including the Orientale complex), and measurements of physical librations are reviewed. Systems for determining the lunar geometry and topography are described along with their intrinsic disadvantages. Tectonic implications of the lunar gravitational field and shape are discussed in regard to thermal evolution, marked variations in elevations, crustal and mascon formation, and volcanism.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: EOS; 56; June 197
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  • 9
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    Early scattering by Jupiter and its collision effects in the terrestrial zone (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: When Jupiter was on the order of three to ten earth masses in size, there undoubtedly was a considerably larger mass of condensed matter in its zone, since Jupiter would have perturbed most of it to other parts of the solar system. Monte Carlo studies indicate a significant portion would have crossed the earth's orbit. If the earth and moon had not yet fully formed, the probability of earth-zone planetesimals being hit by this Jupiter-scattered material was high. Further Monte Carlo models of these collisions and their products indicate a significant portion of matter was heated to melting, even if less than 5% of the relative kinetic energy went into heat. The models include capture probabilities by an embryo earth and a protolunar swarm. Because heat energy is correlated with comminution energy, and because the capture probability of the swarm is mass-dependent while embryo's is not, the protolunar material suffered much higher heating on the average than did the proto-earth material.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 25; May 1975
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  • 10
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    Selenodesy (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Only the second- and third-degree harmonics of the global gravity field are known reliably. The most pronounced features in the near side field are still the mascons, mass excesses in ringed maria. Statistically, the magnitudes of variations in the lunar gravity field for feautres of 150- to 1100-km extent are between one-fourth and one-third those predicted from the earth on the assumption of equal stress implication. Aspects of rotational dynamics and geometry are also discussed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Reviews of Geophysics and Space Physics; 13; July 197
    Format: text
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