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  • LUNAR AND PLANETARY EXPLORATION  (4)
  • COMMUNICATIONS AND RADAR  (1)
  • 1
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    Gravity and topography (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The paper summarizes the fundamental gravity field constants for Mars and a brief historical review of early determinations and current-day accurate estimates. These include the planetary gravitational constant, global figure, dynamical oblateness, mean density, and rotational period. Topographic results from data acquired from the 1967 opposition to the most recent, 1988, opposition are presented. Both global and selected local topographic variations and features are discussed. The inertia tensor and the nonhydrostatic component of Mars are examined in detail. The dimensionless moment of inertia about the rotational axis is 0.4 for a body of uniform density and 0.37621 if Mars were in hydrostatic equilibrium. By comparing models of both gravity and topography, inferences are made about the degree and depth of compensation in the interior and stresses in the lithosphere.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 209-248.
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    NASA TECHNICAL REPORTS
  • 2
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    Relating the Planetary Ephemerides and the Radio Reference Frame (1985)
    In:  CASI
    Details
    Publication Date: 2014-08-26
    Description: The positions of Venus, Mars, and Jupiter were obtained in the VLBI radio reference frame by measuring the position of a satellite (natural or artificial) of each planet relative to an extragalactic source in the radio catalogue. From the results for Mars and Venus it is concluded that the offset in right ascension of the radio frame from the dynamical equinox defined in DE200 is 0.00 sec +/- 0.04 sec. The observations for Jupiter imply a correction to its position from DE200 of -0.18 sec +/- 0.04 sec in right ascension and -0.06 +/- 0.05 sec in declination on 1983 April 29. The right ascension of Jupiter relative to the inner planets has been measured independently using Doppler tracking data near Jupiter encounter from Pioneers 10 and 11 and from Voyagers 1 and 2 by tying the tracking station positions, through previous spacecraft missions, to the DE200 ephemerides of the inner planets. This technique yielded a correction to Jupiter's right ascension of -0.22 +/- 0.05 sec, in good agreement with the results from the direct radio measurements.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. Data Acquisition Rept.; p 1-8
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Venus gravity anomalies and their correlations with topography (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: This report provides a summary of the high-resolution gravity data obtained from the Pioneer Venus Orbiter radio tracking data. Gravity maps, covering a 70 deg latitude band through 360 deg of longitude, are displayed as line-of-sight and vertical gravity. Topography converted to gravity and Bouguer gravity maps are also shown in both systems. Topography to gravity ratios are made over several regions of the planet. There are markedly different ratios for the Aphrodite area as compared to the Beta and Atla areas.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 88; Feb. 10
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  • 4
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    Experimental determination of Mercury's mass and oblateness (1976)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The ratio of the mass of the sun to that of Mercury deduced from the first and third flybys of Mercury by Mariner 10 is 6,023,600 plus or minus 600 and 6,023,700 plus or minus 300, respectively. Additional analysis should improve these uncertainties by a factor of 2 to 5. Assuming an equatorial radius of 2439 km, the mean density of the planet is 5.44 g/cu cm. The gravitational oblateness deduced from the first encounter is discussed. Data received from the third encounter are better suited for this determination and yield J2 of 0.00008 plus or minus 0.00006. In addition, the third-encounter data are sensitive to local gravity effects or anomalies.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Plenary Meeting; Jun 08, 1976 - Jun 19, 1976; Philadelphia, PA
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  • 5
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    Venus gravity - Analysis of Beta Regio (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Radio tracking data acquired over Beta Regio were analyzed to obtain a surface mass distribution from which a detailed vertical gravity field was derived. In addition, a corresponding vertical gravity field was evaluated solely from the topography of the Beta region. A comparison of these two maps confirms the strong correlation between gravity and topography which was previously seen in line-of-sight gravity maps. It also demonstrates that the observed gravity is a significant fraction of that predicted from the topography alone. The effective depth of complete isostatic compensation for the Beta region is estimated to be 330 km, which is somewhat deeper than that found for other areas of Venus.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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