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  • LUNAR AND PLANETARY EXPLORATION  (601)
  • 1980-1984  (601)
  • 1981  (601)
  • 1
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    Curatorial functions and the U.S. Antarctic meteorite program (1981)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The discovery of concentrations of meteorites in Antarctica by Japanese field parties in 1969, and subsequently by joint U.S.-Japanese and U.S. field parties since 1976 has provided a significant new resource for understanding the origin and evolution of the solar system. The number of meteorites as well as the variety of meteorites has increased dramatically, and substantial amounts of data derived from their study has begun to appear in the scientific literature. The U.S. program of investigation has drawn on curatorial experience derived from the lunar program to: (1) develop specific collection and preliminary examination protocols; (2) provide documented samples for scientific investigations in response to specific requests; and (3) coordinate research by scientific consortia. The productivity of scientific research is significantly enhanced by these management approaches. Some of the results of the curatorial program for Antarctic meteorites carried out over the past three years are described.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: National Institute of Polar Research, Memoirs (ISSN 0386-0744); 20, D
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  • 2
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    Development of a window protection assembly for a shuttle experiment (1981)
    In:  CASI
    Details
    Publication Date: 2006-01-16
    Description: A window environmental protection assembly developed for the shuttle infrared leeside temperature experiment is described. The assembly consists of a carbon phenolic composite window mount which contains two silicon windows, a fibrous environmental protection plug to protect the windows during launch operations and ascent heating, a release mechanism used to jettison the plug just prior to atmospheric entry, and two pin puller mechanisms which retain the plug. The plug is released from the window mount assemblies using pneumatic pin pullers and separation springs in the release mechanism. The assembly was designed and tested to withstand the severe mechanical and thermal environments which could be experienced at the top of the shuttle orbiter vertical stabilizer during the ascent, on-orbit, and entry periods of the shuttle trajectory.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA. Marshall Space Flight Center The 15th Aerospace Mech. Symp.; p 303-329
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  • 3
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    The Galilean satellites (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The general characteristics of the Galilean satellites, as determined from Voyager data, are described. Attention is then given to the characteristics (surface features, colors, compositions, and geophysical and geochemical processes) of the particular satellites. Particular consideration is given to the nature of Io's atmosphere and to magnetospheric interactions.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 4
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    Atmospheres of the terrestrial planets (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The paper reviews current knowledge of the characteristics of atmospheres surrounding the terrestrial planets; attention is given to composition, temperature, characteristics of the upper atmospheres, and meteorology. In addition, the long-term history of the atmospheres is discussed, along with some of the major climatic changes that have occurred. Finally, consideration is given to future efforts that will enhance the understanding of these subjects.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 5
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    Near-infrared spectrophotometry of the satellites and rings of Uranus (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: New spectrophotometry from 1.5 to 2.5 microns is reported for the Uranian satellites Titania, Oberon, and Umbriel. A spectrum of the rings of Uranus from 2.0 to 2.4 microns is also reported. No evidence is found for frost covering the surface of the ring material, consistent with the low albedo of the rings previously reported by Nicholson and Jones (1980). The surfaces of the satellites are found to be covered by dirty water frost. Assuming albedos of the frost and gray components covering the Uranian satellites to be the same as the light and dark faces of Iapetus, radii are derived that are roughly twice those inferred from the assumption of a visual albedo of 0.5.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 45; Mar. 198
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  • 6
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    Temporal and spatial variations observed in the ionospheric composition of Venus - Implication for empirical modelling (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The distributions of several ion species in a data base obtained by in situ measurements of the thermal ion composition of the ionosphere of Venus by the Pioneer Venus Orbiter have been sorted to identify temporal and spatial variations and determine the feasibility of an analytical representation of the experimental results. The first results from the sorting of several prominent ions including O(+), O2(+), and H(+) and several minor ions including CO2(+), C(+), and H2(+) reveal significant diurnal variations which consist of strong day to night contrast in the ion concentrations, with differences of one to two orders of magnitude, depending upon ion mass and altitude. It is suggested that repeatable day to night gradients in the ion distribution are adaptable to parametric modeling.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 7
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    Dynamic variations observed in thermal and superthermal ion distributions in the dayside ionosphere of Venus (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: In-situ measurements of the ion composition and concentration of the ionosphere of Venus are obtained with the Bennett RF ion mass spectrometer (OIMS) on the Pioneer Venus Orbiter (PVO). Dayside ion profiles exhibit considerable variability in the height of the ionopause as well as the scale heights of the ion constituents, which reflect the compression and expansion of the ionosphere in response to solar wind variations. Near the dayside upper boundary of the thermal O+ distribution, super-thermal ions are detected by the OIMS, presenting a complication for identifying the ion signature of the ionopause. Correlated with the presence of the superthermal ions, the ac electric field detector (OEFD) detects regions of intensified signals, with peak response in the 100 Hz frequency channel. It is expected that further analysis of the superthermal ion-electric field signatures will contribute to a clearer understanding of the physical processes underlying the formation of the ionopause.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 8
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    The electrodynamic interaction of Io with Jovian magnetosphere (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 9
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    Bidirectional reflectance spectroscopy. II - Experiments and observations (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Aspects of the theoretical bidirectional reflectance expression derived by Hapke (1981) are studied experimentally, and it is shown that the expression describes satisfactorily the measured angular scattering and spectral properties of a cobalt glass powder in which the two properties vary greatly with wavelength. The theoretical reflectance function also describes measured distributions of intensity across the surfaces of planets, except near the sunlit limb, where the macroscopic roughness influences the brightness.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Apr. 10
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  • 10
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    Observations of Martian tides over two annual cycles (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The first four diurnal surface pressure harmonics have been analyzed over major portions of two Martian annual cycles (Mars years) at the two Viking lander sites. The diurnal harmonics of surface wind have also been analyzed at one of the sites. Since the atmospheric tides have previously been shown to provide a good indication of Martian global dust storms, these results provide a basis for comparing dust storm activity in the two years. Two global dust storms occurred during the first year. During the second year, there was only one major storm, and it closely followed the pattern of the first storm of the first year. A significant feature of the results is the brief, but nearly complete, vanishing of the diurnal pressure tide at the onset of one of the global dust storms. It is proposed that this may have been due to interference between the normal westward-propagating diurnal tide and a topographically forced eastward propagating tide, and that the latter may have helped initiate the global storm.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of the Atmospheric Sciences; 38; Jan. 198
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  • 11
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    A Martian general circulation experiment with large topography (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A three-layer general circulation model of the Martian atmosphere is described, and the assumptions governing the model are discussed. The simulated, zonally averaged circulation is found to have only limited sensitivity to differences between this model and an earlier general circulation model; this circulation compares reasonably well with observations. It is also found that the meridional mass flow produced by the seasonal condensation of CO2 in the winter polar region has a major influence on the circulation; owing to the weak influence of atmospheric heat transport, however, the mass flow is governed almost entirely by radiation. Quasi-barotropic stationary waves, which are forced kinematically by the topography and which resemble topographically forced terrestrial planetary waves, are generated by the model in the winter hemisphere region of strong eastward flow, while baroclinic stationary waves are thermally forced by topography in the tropics and summer subtropics. It is also concluded that transient baroclinically unstable waves, of somewhat lower dominant wavenumber than those found on the earth, are generated in winter midlatitudes; their amplitudes, wavenumbers, and phase speeds closely agree with what has been deduced from the Viking lander observations.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of the Atmospheric Sciences; 38; Jan. 198
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  • 12
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    Meteoric ion production near Jupiter (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Meteoric ion layer formation within the Jovian atmosphere is examined with attention to metallic ion production in the lower ionosphere. The Fe(+) impact ionization rate within the Jovian atmosphere peaks above the mesopause with a magnitude of approximately 0.5 cu cm/sec and is much less than the ambient ionosphere photoionization rates near the late afternoon Pioneer 10 ionosphere occultation. Charge exchange of the ablated neutral Fe atoms with ambient ions can result in an Fe(+) production rate of about 10 cu cm/sec. Ignoring transport, steady state Fe(+) density maxima of about 10,000 or 1,000,000 cu cm can be maintained when Fe(+) loss is through radiative association or radiative recombination respectively. Even if an estimated lower limit to the incident meteoroid flux is used based on a meteoroid spatial density which does not vary with distance from the sun, the corresponding Fe(+) peak densities are 1,000 and 500,000 cu cm, respectively. Meteoric ion densities may thus be important in the Jovian lower ionosphere.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Mar. 1
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  • 13
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    Discovery of natural gain amplification in the 10-micrometer carbon dioxide laser bands on Mars - A natural laser (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Fully resolved intensity profiles of various lines in the carbon dioxide band at 10.4 micrometers have been measured on Mars with an infrared heterodyne spectrometer. Analysis of the line shapes shows that the Mars atmosphere exhibits positive gain in these lines. The detection of natural optical gain amplification enables identification of these lines as a definite natural laser.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 212; Apr. 3
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  • 14
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    Earthquakes - on the moon (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Information obtained with the Apollo lunar seismic stations is discussed. The four types of natural seismic sources that have been identified are described, viz., thermal moonquakes, deep moonquakes, meteoroid impacts, and shallow moonquakes. It is suggested that: (1) the thermal quakes represent the slow cracking and movement of surface rocks; (2) the deep quakes are induced by the tide-generating force of the earth's gravity; (3) the meteoroids responsible for most of the observed impacts are in the mass range from 1 to 100 kg and are clustered in groups near the earth's orbit; and (4) the shallow quakes are similar to intraplate earthquakes and indicate that the moon is as seismically active as the interior regions of the earth's tectonic plates. The structure of the lunar interior as inferred from seismic signals due to both the last three natural sources and 'artificial' impacts of used spacecraft is examined in detail.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Discovery; 6; 1, 19; 1981
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  • 15
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    The atmosphere and ionosphere of Jupiter (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The thermal structure of the upper atmosphere of Jupiter, the composition of the atmosphere and the strength of mechanical mixing, and sources and sinks of ionization in the Jupiter ionosphere are described from Voyager UV spectrometer, radio, IR, and imaging data. A topside ionospheric temperature of 1300 K was observed, along with an energy equilibrium between the plasma and neutral gas in the upper atmosphere. A composite thermal structure is provided, noting a close similarity to earth conditions at upper levels, and enhanced thermal behavior has been detected between the times of solar minimum and maximum activity. Ammonia photochemistry is examined, and measured concentrations of H2, CH4, C2H6, and C2H2 as a function of height are outlined. Eddy diffusion coefficient calculations are carried out, yielding a highest Ly-alpha intensity of 100 million sq cm/sec. The increased exospheric temperature between 1973 and 1980 is stressed to have no known satisfactory explanation.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Vistas in Astronomy; 25; pt. 3
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  • 16
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    Martian channels and valleys - Their characteristics, distribution, and age (1981)
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    Publication Date: 2011-08-18
    Description: The distribution and ages of Martian channels and valleys, which are generally believed to have been cut by running water, are examined with particular emphasis on the small branching networks referred to as runoff channels or valley networks. Valleys at latitudes from 65 deg S to 65 deg N were surveyed on Viking images at resolutions between 125 and 300 m. Almost all of the valleys are found in the old cratered terrain, in areas characterized by high elevations, low albedos and low violet/red ratios. The networks are deduced to have formed early in the history of the planet, with a formation rate declining rapidly shortly after the decline of the cratering rate 3.9 billion years ago. Two types of outflow channels are distinguished: unconfined, in which broad swaths of terrain are scoured, and confined, in which flow is restricted to discrete channels. Both types start at local sources, and have formed episodically throughout Martian history. Fretted channels, found mainly in two latitude belts characterized by relatively rapid erosion along escarpments, are explained by the lateral enlargement of other channels by mass wasting.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 48; Oct. 198
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  • 17
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    Venus nightside ionospheric holes - The signatures of parallel electric field acceleration regions (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Attention is given to the existence of 'holes', that is, regions of density depletion in the nightside Venus ionosphere associated with regions of radial magnetic fields. The properties of the electrons within the core of these holes are thought to suggest an acceleration process along the magnetic field lines, a process also suggested by the Venera 9 and 10 observations of energetic ions in the Venus tail. On the basis of the observational information, these Venusian plasma depletions are attributed to the presence of parallel electric fields similar to those observed in the terrestrial auroral ionosphere. The resulting electric field accelerates electrons down the field lines, heating the depleted thermal electron population within the hole and producing ionization below the hole. At the same time, ionospheric ions are accelerated outward toward the plasmasheet.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters; 8; Dec. 198
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  • 18
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    Fresnel zone structure in planetary occultations (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The structures of the Fresnel zones of an occulting body with a substantial atmosphere are analyzed. The first Fresnel zone is defined as the set of all contiguous points connected to the transmitter and receiver via paths with a combined length within one half wavelength of the stationary value, and calculated by the application of the Huygens-Fresnel principle to a wave front frozen in time as it traverses the region of interest, taking into account wave front curvature of waves undergoing refraction. Calculations of the Fresnel zones of a planet determined by the meeting of wave fronts represented as tori reveal that the zone along the propagation path traversing the nearest portion of the limb to the transmitter has a shape similar to an ellipse, while that of the far zone resembles the letter X. The phase delay along the farside path is found to be a stationary point rather than a minimum, since delay is distributed in the form of a hyperbolic paraboloid near the ray and in the form of a torus intersection for greater separations. Examples are presented for S band propagation deep in the atmospheres of Venus and Jupiter.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Radio Science; 16; Nov
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  • 19
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    Topography of Venus and earth - A test for the presence of plate tectonics (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Comparisons of earth and Venus topography by use of Pioneer/Venus radar altimetry are examined. Approximately 93% of the Venus surface has been mapped with a horizontal resolution of 200 km and a vertical resolution of 200 m. Tectonic troughs have been indicated in plains regions which cover 65% of Venus, and hypsometric comparisons between the two planets' elevation distributions revealed that while the earth has a bimodal height distribution, Venus displays a unimodal configuration, with 60% of the planet surface within 500 m of the modal planet radius. The effects of mapping the earth at the same resolution as the Venus observations were explored. Continents and oceans were apparent, and although folded mountains appeared as high spots, no indications of tectonic activity were discernible. A NASA Venus Orbiting Imaging radar is outlined, which is designed to detect volcanoes, folded mountain ranges, craters, and faults, and thereby allow definition of possible plate-tectonic activity on Venus.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: American Scientist; 69; Nov
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  • 20
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    Observations of Saturn in the 5- to 8-micron spectral region (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A spectrum of Saturn obtained from the Kuiper Airborne Observatory exhibits an emission peak at 6.8 microns attributed to ethane, but is otherwise dominated by absorption from 5.3 to 7.2 microns. While the large absorption in this spectral region is consistent with the presence of ammonia gas or ammonia ice, or both, such an explanation is inconsistent with the lack of a major absorption near 3.0 microns.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 45; Mar. 198
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  • 21
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    Martian ages (1981)
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    Publication Date: 2011-08-18
    Description: Four discussions are conducted: (1) the methodology of relative age determination by impact crater statistics, (2) a comparison of proposed Martian impact chronologies for the determination of absolute ages from crater frequencies, (3) a report on work dating Martian volcanoes and erosional features by impact crater statistics, and (4) an attempt to understand the main features of Martian history through a synthesis of crater frequency data. Two cratering chronology models are presented and used for inference of absolute ages from crater frequency data, and it is shown that the interpretation of all data available and tractable by the methodology presented leads to a global Martian geological history that is characterized by two epochs of activity. It is concluded that Mars is an ancient planet with respect to its surface features.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Apr. 10
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  • 22
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    Bidirectional reflectance spectroscopy. I - Theory (1981)
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    Publication Date: 2011-08-18
    Description: An approximate analytic solution is derived for the radiative transfer equation describing particulate surface light scattering, taking into account multiple scattering and mutual shadowing. Analytical expressions for the following quantities are found: bidirectional reflectance, radiance coefficient and factor, the normal, Bond, hemispherical, and physical albedos, integral phase function and phase integral, and limb-darkening profile. Scattering functions for mixtures can be calculated, as well as corrections for comparisons of experimental transmission or reflection spectra with observational planetary spectra. The theory should be useful for the interpretation of reflectance spectroscopy of laboratory surfaces and the photometry of solar system objects.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Apr. 10
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  • 23
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    Spectra of the Jovian ring and Amalthea (1981)
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    Publication Date: 2011-08-18
    Description: Measurements made between 0.887 and 2.4 microns demonstrate that the Jovian ring and Amalthea have similar reflection spectra. The spectra, in particular the ratio of the 0.9- to 2.2-micron reflectivities, are inconsistent with those expected from water, ammonia, or methane frosts, but are consistent with reflection from large rock bodies.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astronomical Journal; 86; Apr. 198
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  • 24
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    Voyager measurement of the rotation period of Saturn's magnetic field (1981)
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    Publication Date: 2011-08-18
    Description: Saturn's radio rotation period is determined using measurements made by the Planetary Radio Astronomy experiment onboard the Voyager spacecraft. The sidereal period deduced is 10 hr 39 min 24 sec + or 7 sec. The radio rotation period is presumably that of the planet's magnetic field. A provisional Saturn longitude convention is proposed, and equations are provided to compute a longitude emphemeris and to transform between the proposed system and the (10 hr 14 min) system used for the Pioneer 11/Saturn encounter. In addition, the degree of longitude smearing which could result over the long term from the merging of data sets organized in this system is evaluated. Finally, no evidence of control of the radio emission by any of Saturn's satellites is found.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters; 8; Mar. 198
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  • 25
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    Radio science investigations of the Saturn system with Voyager 1 - Preliminary results (1981)
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    Publication Date: 2011-08-18
    Description: Analyses of Voyager 1 radio occultation measurements of the Saturn atmosphere near 75 deg south latitude and of the Titan equatorial atmosphere are presented. Molecular nitrogen appears to be the primary atmospheric constituent of Titan, whose clouds are probably methane ice. Solar abundance considerations of the data suggest large quantities of surface methane near its triple-point temperature, so that the three phases of methane could play a role on Titan analogous to that of water on earth. Ionospheric electron concentration and plasma scale height for the Saturn polar cap and monochromatic attenuation of the Saturn rings are also considered, along with radio tracking figures for the masses of two moons, Rhea and Titan.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 212; Apr. 10
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  • 26
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    Infrared observations of the Saturnian system from Voyager 1 (1981)
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    Publication Date: 2011-08-18
    Description: Atmospheric chemistry analyses of Saturn based on Voyager 1 infrared spectral and radiometric data are presented, including characteristics of the planet's rings and of Titan and other satellites. Infrared spectra of Saturn indicate the presence of H2, CH4, NH3, PH3, C2H2, and C2H6, with the possibility of C3H4 and C3H8. The atmospheric thermal structure of the planet shows hemispheric asymmetries that are consistent with seasonally varying insolation response, with an extensive small-scale latitudinal structure. Atmospheric chemistries of Titan, and optical and thermal characteristics for the rings of Saturn, are also given.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 212; Apr. 10
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  • 27
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    Comparative aspects of Venus and terrestrial meteorology (1981)
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    Publication Date: 2011-08-18
    Description: The observations and measurements made by Pioneer Venus orbiters are presented in terms of comparison of Venus and terrestrial meteorology. Although the temperature-pressure profiles of the two planets differ at lower altitudes, the temperatures are similar over their common range of pressures except for a much cooler mesosphere on Venus. The additional similarities between the earth and Venus relate to the warm polar stratospheres and the zonally-averaged energy budgets of the two planets. A difference in the mean radiation budgets for Venus is the relative smallness of the upward and downward thermal flux components. It is noted that the observed similarities reflect common mechanisms despite the difference in the dynamical regimes of the two planets.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Weather; 36; Feb. 198
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  • 28
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    Earthlike planets: Surfaces of Mercury, Venus, earth, moon, Mars (1981)
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    Publication Date: 2011-08-18
    Description: The surfaces of the earth and the other terrestrial planets of the inner solar system are reviewed in light of the results of recent planetary explorations. Past and current views of the origin of the earth, moon, Mercury, Venus and Mars are discussed, and the surface features characteristic of the moon, Mercury, Mars and Venus are outlined. Mechanisms for the modification of planetary surfaces by external factors and from within the planet are examined, including surface cycles, meteoritic impact, gravity, wind, plate tectonics, volcanism and crustal deformation. The origin and evolution of the moon are discussed on the basis of the Apollo results, and current knowledge of Mercury and Mars is examined in detail. Finally, the middle periods in the history of the terrestrial planets are compared, and future prospects for the exploration of the inner planets as well as other rocky bodies in the solar system are discussed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 29
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    Jupiter's magnetopause, bow shock, and 10-hour modulated magnetosheath Voyagers 1 and 2 (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: This summary report discusses Jupiter's magnetopause, bow shock and magnetosheath, based on fine scale magnetic field data from the Voyager 1 and 2 encounters. Explicit models of the dawnside magnetopause and bow shock in Jupiter's orbital plane employ an axisymmetric parabola and hyperbola, respectively, and satisfy average boundary crossing positions, inbound and outbound; these models are determined separately for the two encounters. A new phenomenon has been discovered in Jupiter's magnetosheath. It is manifested as (5 or) 10 hour quasi-periodic modulation of the direction of the magnetic field in the outbound magnetosheath, predominantly in the northward (N) and southward (S) directions. It was seen to occur during both encounters and appears most evident in Voyager 2 outbound observations.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters; 8; Jan. 198
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    A model of temporal variations in ozone density in the Martian atmosphere (1981)
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    Publication Date: 2011-08-18
    Description: Temporal variations of the ozone density profile in the Martian atmosphere at high latitudes are calculated for the course of a Martian year, taking into account seasonal and diurnal variations in temperature, water vapor and solar radiation. Calculations are based on a model including 35 neutral photochemical reactions, and vertical eddy diffusion using a time step of 12 min for the region from the surface to 240 km altitude. Results are found to be in better agreement with Mariner 9 observations of the time and magnitude of the seasonal maximum than previous model calculations. The diurnal variation is predicted to be small near the solstices, with the nighttime ozone density greater than the daytime and the magnitude of the difference dependent on season. Opposite temporal variations are predicted for ozone densities above and below about 25 km, and an ozone density maximum at 35-40 km is obtained. It is suggested that the effects of an aerosol layer may not be important in enhancing predicted ozone concentration, and may even decrease it.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Planetary and Space Science; 29; Jan. 198
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    Ultraviolet emissions from the upper atmospheres of the planets (1981)
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    Publication Date: 2011-08-18
    Description: Some recent results on planetary upper atmospheres obtained by means of orbiting ultraviolet observatories are reviewed with emphasis on Jupiter and Io torus. Consideration is given to long-term variation in Jovian Ly alpha emission, UV polar auroras on Jupiter, and UV emission from the Io torus. Requirements for UV planetary astronomy are briefly discussed.
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    Jovian magnetic models and the polarization angle of Jovian decimetric radiation (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A comparative study of the direction of linear polarization of Jovian decimetric (synchrotron) radiation as measured astronomically and as determined from a model of the inner Jovian magnetosphere is discussed. It is noted that the model depicts the radiation as coming from rings of relativistic electrons in the Jovimagnetic equator at varying radial distances from the center of the planet. The equator is determined through each of two magnetic representations - the O4 model of Acuna and Ness (1976) and the P10-11 model of Smith et al. (1976) - derived from in situ Pioneer magnetometer measurements. Deviations from a (planar) dipole equator are found to occur at nearly all longitudes in both models; no evidence is found for a longitudinally localized magnetic anomaly.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal; vol. 245
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    Configuration of Jupiter's magnetic tail and equatorial current sheet (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Recent research reports by Behannon et al. (1981) and Connerney et al. (1981) are summarized. It is noted that the analysis made of the detailed neutral sheet crossings by the minimum variance method shows a consistent result with regard to the orientation of the neutral sheet in the magnetic tail as a two-dimensional surface rocking back and forth about the Jupiter sun-line as the rotation of the planet leads to a precession of the tilted dipole magnetic axis. The occurrence of neutral sheet crossings is found not to be consistent with any of the axially symmetric theoretical models proposed earlier on the basis of the 1974 Pioneer 10 observations. It is noted that a simple nonaxially symmetric model has been developed on the basis of the Voyager results which indicates the strong control upon orientation by the interaction of the solar wind with the Jovian magnetosphere. The model is described as simple because it improves the fit of theory to observation but uses fewer parameters. A quantitative model of the magnetodisc equatorial current sheet has been developed for the inner magnetosphere region which matches well the in-situ magnetic field observations.
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    The Venus ionosphere as an obstacle to the solar wind (1981)
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    Publication Date: 2011-08-18
    Description: Pioneer Venus Orbiter Electron Temperature Probe measurements of hundreds of bow shock and ionopause crossings are employed in describing the configuration of these two boundaries and their variations in response to changes in solar wind pressure. The average bow shock configuration is found to be well represented by an Archimedian hyperboloid whose altitude at the subsolar point is 0.46 Venus radii, a value slightly greater than that derived from Pioneer Venus magnetometer data using a fit to a general conic section. It is noted that the average bow shock configuration exhibits a high degree of azimuthal symmetry near the terminator. The orbit to orbit variability of the shock location is unexpectedly large, the standard deviation being about 10%. A tendency is noted for the bow shock and the ionopause to expand and contract simultaneously, but the weakness of their orbit by orbit correlation suggests that the ionopause of Venus is not the only obstacle to the solar wind. It is thought that such processes as photoion pickup and charge exchange with neutrals may be important in diverting the solar wind plasma around the planet.
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    Investigation of some of the principal geometric effects on planetary polarization (1981)
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    Publication Date: 2011-08-18
    Description: The paper investigates geometric effects which may influence the interpretation of observed polarimetric data of planets used to deduce physical properties of aerosols and their distributions in planetary atmospheres. The effects studied include the observer's distance to the planet, horizontal inhomogeneity of the planetary atmosphere, and deviation from a spherical body. The results will facilitate the present and future analyses of spacecraft data.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Moon and the Planets; 24; May 1981
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    H2 abundance in the atmosphere of Venus (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The in situ measurements from the Pioneer Venus Orbiter (PVO) Ion Mass Spectrometer have led to the detection of H2(+) ions in the Venus ionosphere. Although H2(+) is a minor ion, its measurement provides the first direct clue for determining the H2 abundance in the upper atmosphere of Venus. A photochemical model using PVO measurements is used to derive an H2 mixing ratio of 10 ppm below 140 km altitude. The presence of this much H2 confirms a previous prediction that the reactions of O(+) with H2 and subsequent recombination of OH(+) provide an important source of nonthermal H observed in the Venus atmosphere. The estimated escape flux for H is 10 to the 8th per sq cm/s.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters; 8; Mar. 198
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    Magnetic field studies by Voyager 1 - Preliminary results at Saturn (1981)
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    Publication Date: 2011-08-18
    Description: Confirmation and refinement of Saturnian magnetosphere features established by the Pioneer 11 emission are claimed for Voyager 1 magnetic field studies of the planet. The radius of the magnetopause at the subsolar point is 23 Saturn radii, and a magnetic tail of 80 Saturn radii diameter was discovered. The tail extends away from the sun and is similar to both type II comet tails and the terrestrial and Jovian magnetic tails. Data from Voyager's very close flyby of Titan, which is located within the Saturn magnetosphere, shows an absence of any substantial, intrinsic satellite magnetic field.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 212; Apr. 10
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    Lineament and polygon patterns on Europa (1981)
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    Publication Date: 2011-08-18
    Description: A classification scheme is presented for the lineaments and associated polygonal patterns observed on the surface of Europa, and the frequency distribution of the polygons is discussed in terms of the stress-relief fracturing of the surface. The lineaments are divided on the basis of albedo, morphology, orientation and characteristic geometry into eight groups based on Voyager 2 images taken at a best resolution of 4 km. The lineaments in turn define a system of polygons varying in size from small reticulate patterns the limit of resolution to 1,000,000 sq km individuals. Preliminary analysis of polygon side frequency distributions reveals a class of polygons with statistics similar to those found in complex terrestrial terrains, particularly in areas of well-oriented stresses, a class with similar statistics around the antijovian point, and a class with a distribution similar to those seen in terrestrial tensional fracture patterns. Speculations concerning the processes giving rise to the lineament patterns are presented.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 289; Jan. 8
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    Rings in the solar system (1981)
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    Publication Date: 2011-08-18
    Description: The structure and composition of the rings of Jupiter, Saturn, and Uranus are discussed, with special attention given to the rings of Saturn. Processes that are known to shape the rings are then described. Alternative explanations for the origin of the rings are proposed. It is pointed out that the architecture of a ring system results from the interplay of a number of forces, among them gravitational forces due to moons outside the rings and the moonlets embedded in them, electromagnetic forces due to the planet's rotating magnetic field, and even the gentle forces exerted by the dilute gaseous medium in which the rings rotate.
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    Daily and seasonal Viking observations of Martian bore wave systems (1981)
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    Publication Date: 2011-08-18
    Description: A Martian atmospheric phenomenon called a bore wave has been observed by the Viking imaging system during late spring and early summer of two Martian years, in the Tharsis Ridge region of the planet. The observational data are presented, and a tentative explanation is offered for the occurrence of this feature, formed by airflow and which behaves like a thermally induced diurnal katabatic breeze.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 293; Oct. 22
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    Minor planets and related objects. XXIX - Asteroid 29 Amphitrite (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: UBV photometry and lightcurves of asteroid 29 Amphitrite from all observed apparitions (March 1956-May 1977) are combined to obtain a phase function having a linear phase coefficient of 0.030 + or - 0.002 mag/deg and a mean absolute magnitude of 6.19 + or - 0.04. Amphitrite displays a reddening of its B - V color index with increasing solar phase angle: 0.816 + or - 0.004 at a phase angle of 2 deg and 0.848 + or - 0.004 at 23 deg. Since Amphitrite's orbital inclination is low (6 deg) and its lightcurve amplitudes range between 0.06 and 0.11 mag, and are well distributed in longitude, it is concluded that the obliquity of its pole is significantly different from zero. During some apparitions Amphitrite's light curves display only one maximum and minimum per 5.3904 + or - 0.007-hr rotation period while in others as many as five of each are present. This is interpreted to mean that Amphitrite has a quasi-spherical shape with a highly irregular and/or variegated surface.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astronomical Journal; 86; Oct. 198
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    Thermal structure and dynamics of the Jovian atmosphere. II - Visible cloud features (1981)
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    Publication Date: 2011-08-18
    Description: Thermal structures including major white ovals, hot spot regions, barges and a belt zone pair in the Jovian atmosphere are investigated using Voyager IRIS data. Atmosphere above anticyclonic features is cold relative to the immediate surroundings in the upper troposphere and tropopause region, which is consistent with upwelling and divergence in that part of the atmosphere. Localized cyclonic features are warm relative to their surroundings which implies subsidence with accompanying convergence. Thermal wind shear indicates a decay of the vorticity with height in the upper troposphere and lower stratosphere, and vertical velocities imply an upper limit of vertical mixing times near the tropopause of about 20 years. Various possible models are also examined, including radiative heating, vertical wave propagation, and thermally indirect merdional cells.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Sept. 30
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    Flow fields within Jupiter's Great Red Spot and White Oval BC (1981)
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    Publication Date: 2011-08-18
    Description: Voyager 1 high-resolution images of Jupiter's Great Red Spot (GRS) and White Oval BC are used to map flow fields within these two areas. The relative vorticity is computed as a function of semi-major axis length and position angle in a coordinate system consisting of concentric ellipses of equal eccentricity. Wind speeds of 110-120 m/s are observed near the outer edge of both features, and along their minor axes relative vorticity profiles reach a maximum of 0.00006/s. Maximum Rossby numbers of 0.36 are computed for flows within both features, and are found to be low, indicating geostrophic constraints on the flow. The difference in streamline curvature within the GRS and the Oval BC is found to compensate for the difference in planetary vorticity at the respective latitudes of the features. Finally, motions within the central region of the GRS are slower and more random than around the spot's outer portion.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Sept. 30
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    Thermal structure and dynamics of the Jovian atmosphere. I - The Great Red Spot (1981)
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    Publication Date: 2011-08-18
    Description: Temperatures and thermal winds over the Great Red Spot (GRS) are derived from Voyager IRIS data for atmospheric pressures between 3 and 500 mbar. A cold tropopause implies a decrease in anticyclonic vorticity with height above 500 mbar through the lower stratosphere. Observations at 5 microns indicate that there is little emission from the GRS itself, although there is enhanced emission from a ring around it. The behavior of the tropopause and 5 micron temperatures are considered to be results of circulation which rises within the GRS and subsides in the area around it. Results are discussed in the context of several theoretical models of the GRS, and latent heat release as an energy source is considered. Dynamical scalings based on an axisymmetric frictionally controlled vortex indicate that the large-scale dynamics of the GRS are linear, as opposed to those of a tropical cyclone which are nonlinear.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Sept. 30
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    Interaction of eddies and mean zonal flow on Jupiter as inferred from Voyager 1 and 2 images (1981)
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    Publication Date: 2011-08-18
    Description: Voyagers 1 and 2 narrow angle frames are used to obtain displacements of features at resolutions of 130 km over time intervals of 1 Jovian rotation. It is shown that the mean zonal velocity profile does not change by a measurable amount between Voyagers 1 and 2, which is consistent with previous observations. It is also shown that the curvature of the velocity profile vanes varies with latitudes in the range from -3 beta to +2 beta. The barotropic stability criterion is violated at 10 latitudes between + and - 60 deg, and the rate of conversion of eddy kinetic energy into zonal mean kinetic energy is in the range from 1.5 to 3.0 per sq Wm for a layer 2.5 bar deep. The rate of energy conversion is more than 10% of the total infrared heat flux for Jupiter, as compared to the earth where it is only 0.1% of the infrared, which suggests that the two planets possess fundamentally different thermomechanical energy cycles.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Sept. 30
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    The atmosphere of Jupiter - An analysis of the Voyager radio occultation measurements (1981)
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    Publication Date: 2011-08-18
    Description: Coherently related S and X band signals of 2.3 and 8.4 GHz, respectively, which were transmitted from Voyagers 1 and 2 were used to probe the Jovian atmosphere. Height profiles of the gas refractivity, molecular number density, pressure, temperature, and microwave absorption in the troposphere and stratosphere were observed at latitudes ranging from 0 to 70 deg S. At 1000 mbar, the temperature was + or - 5 K and the lapse rate was equal to the adiabatic value of 2.1 K/km within the resolution of the measurements. The ammonia abundance in this region was 0.022 + or - 0.008%, which is in good agreement with values derived from cosmic abundance considerations. The tropopause at the 140 mbar level had a temperature of 110 K, which increased with increasing altitude, reaching 160 + or - 20 K in the 10 to 1 mbar region. Significant horizontal density variations were detected in the stratosphere, which implies a nonuniform temperature and aerosol distribution across the Jovian disk or across high- and low-pressure regions due to local atmospheric dynamics.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Sept. 30
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    Albedo, internal heat, and energy balance of Jupiter - Preliminary results of the Voyager infrared investigation (1981)
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    Publication Date: 2011-08-18
    Description: Full disk measurements recorded by the 0.4-1.7 micron radiometer on Voyager 1 indicate a geometric albedo of 0.274 + or - 0.013. This measurement and the Pioneer-based phase integral of 1.25 yield a Jovian Bond albedo of 0.343 + or - 0.032. Infrared spectra yield a thermal emission of 1.359 + or - 0.014 x .001 W/sq cm, which corresponds to an equivalent blackbody temperature of 124.4 + or - 0.3 K. In addition, the internal heat flux of Jupiter is estimated to be 5.444 + or - 0.425 x .0001 W/sq cm, and the energy balance defined as the ratio of emitted thermal to absorbed solar energy is 1.668 + or - 0.085.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Sept. 30
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    The helium abundance of Jupiter from Voyager (1981)
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    Publication Date: 2011-08-18
    Description: The helium abundance in the Jovian atmosphere is derived from Voyager 1 data by two methods. The first method uses only infrared spectra from selected locations on the planet while the second method uses a thermal profile independently derived from radio occultation measurements and infrared spectra recorded near the occultation point. A hydrogen mole fraction of 0.897 plus or minus 0.030 is obtained from the first method, while the second method gives 0.880 plus or minus 0.036, corresponding to helium mass fractions of 0.19 plus or minus 0.05 and 0.21 plus or minus 0.06, respectively. The estimated errors for the first method are primarily due to systematic uncertainties in the H2 and He absorption coefficients, while those for the second method result mainly from errors in the radio occultation profile and are less well known. Random errors in the measured infrared spectra are found to be negligible in both cases. The results are consistent with a uniform mix of hydrogen and helium within Jupiter's interior, but a modest amount of helium depletion (Delta Y equal to or less than 0.05) cannot be excluded.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Sept. 30
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    Volcanic eruptions on Io (1981)
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    Publication Date: 2011-08-18
    Description: Nine eruption plumes which were observed during the Voyager 1 encounter with Io are discussed. During the Voyager 2 encounter, four months later, eight of the eruptions were still active although the largest became inactive sometime between the two encounters. Plumes range in height from 60 to over 300 km with corresponding ejection velocities of 0.5 to 1.0 km/s and plume sources are located on several plains and consist of fissures or calderas. The shape and brightness distribution together with the pattern of the surface deposition on a plume 3 is simulated by a ballistic model with a constant ejection velocity of 0.5 km/s and ejection angles which vary from 0-55 deg. The distribution of active and recent eruptions is concentrated in the equatorial regions and indicates that volcanic activity is more frequent and intense in the equatorial regions than in the polar regions. Due to the geologic setting of certain plume sources and large reservoirs of volatiles required for the active eruptions, it is concluded that sulfur volcanism rather than silicate volcanism is the most likely driving mechanism for the eruption plumes.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Sept. 30
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    Models for Jupiter's decametric arcs (1981)
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    Publication Date: 2011-08-18
    Description: Arc-shaped structures that dominate Jupiter's decametric emission are discussed in terms of a magnetic fine structure. The sequence of arcs manifest the occurence of widespread fine structures similar to the white ovals on Jupiter's visible surface. An arc concave toward increasing time occurs at the east limb passage, and an arc convex occurs at the west limb passage, which is consistent with the early source producing vertex early arcs, and the late source producing vertex late arcs. Due to the geometry of the Io plasma torus (IPT) which is arranged so that Io skims the northern surface of the IPT, for any connection between Io and Jupiter's surface that involves Alfven waves, the propagation time, the refraction and the directional defocusing of these waves must be strongly influenced by the amount of Alfven wave path length between the instantaneous position of Io and the surface of the IPT.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Sept. 30
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    Effect of the size distribution on the thermal emission from cometary dust (1981)
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    Publication Date: 2011-08-18
    Description: The IR thermal emission from cometary dust is analyzed by two size distribution functions, Sekanina A and a modified Sekanina Miller distribution. The resulting thermal emission spectra are illustrated for heliocentric distances 0.15 to 1.6 AU. The Sekania A distribution does not predict the observed heliocentric variation in the flux ratio I (4.8 micron) I (3.5 micron) for bright comets. A size distribution intermediate between the two presented is a better representation of the dust in recently observed comets.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: ESA The Comet Halley Dust and Gas Environ.; p 67-75
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    The derivation of Halley parameters from observations (1981)
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    Publication Date: 2011-08-18
    Description: Nominal value model parameters for the nucleus (size, mass, rotation, albedo, hydrogen production) the dust and gas for P/Halley at 0.9 AU postperihelion are derived from the light curve and spectra of Halley and by modeling the effect of the nongravitational forces, e.g., the outgassing rocket type effect of the nucleus. In those cases where Halley observations are not sufficient, the average value derived from a larger set of other comets is used, or data from comet Bennett, Halley's best analog, are taken. A flow diagram shows how the parameter values are derived and to what extent these derived values are interdependent.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: ESA The Comet Halley Dust and Gas Environ.; p 19-24
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    Observations of the magnetic field and plasma flow in Jupiter's magnetosheath (1981)
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    Publication Date: 2011-08-18
    Description: A comprehensive description is given of the Jovian MS magnetic fields, and explanations of these phenomena are proposed. While emphasizing Voyager 1 and 2 magnetic field observations and their relations to the plasma observations, it is also shown that the same phenomena are present in the Pioneer 10 magnetic field data. An unusually high occurrence of nearly north or south fields is observed in the outbound MS, especially in the vicinity of the MP. It is noted that the outbound MS fields and their variations tend to occur in a plane parallel to the local MP, according to large scale MP models.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Sept. 30
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    Rectification and enhancement of three severely distorted images of Jupiter's north polar region (1981)
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    Publication Date: 2011-08-18
    Description: A number of high-resolution images of Jupiter's northern hemisphere were received from the imaging photopolarimeter (IPP) aboard Pioneer 11 in 1974. Erratic scanning of the IPP caused severe distortions in three scientifically important images, which until now have never been satisfactorily restored. New rectification and enhancement techniques, implemented on up-to-date image processing hardware, yielding images of sufficient quality to enable full scientific exploitation of the photometric data are reported.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Applied Optics; 20; Oct. 15
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    The morphology and evolution of Ganymede and Calisto (1981)
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    Publication Date: 2011-08-18
    Description: Images of Ganymede and Callisto, Jupiter's two largest moons, among the largest known predominantly icy planetary objects, were obtained by the two Voyager spacecraft. Voyager images were used to investigate the surface characteristics, geologic processes, and internal evolution of Ganymede and Callisto. Ganymede shows two principal types of terrain: one dark, old, and heavily cratered; and another brighter, younger, and characterized by complex patterns of grooves. Voyager imagers were used to determine photometric properties of surface features on both bodies at phase angles up to 120 deg. Surface temperatures are calculated for the major terrain types. Callisto is found to be somewhat warmer than Ganymede. The temperature difference between grooved and cratered terrain on Ganymede is small. A model for the origin of grooved terrain is considered in which extension creates broad, downdropped rift zones in the crust that are filled with water or ice from below.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA. Washington Advan. in Planetary Geol.; p 369-718
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    The stochastic evolution of asteroidal regoliths and the origin of brecciated and gas-rich meteorites (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A model is constructed which views regolith evolution on asteroids as a stochastic process. Average values are shown to be poor descriptors of regolith depth. The utility of the average depth is not significantly increased by avoiding large craters or thick ejecta deposits, a procedure adopted in previous regolith studies. The statistical uncertainty associated with regolith depth severely limits the power of regolith models in predicting parent-body size for brecciated meteorites. A Monte Carlo algorithm was used to simulate the random walks and corresponding charged-particle irradiation histories of grains in regoliths. On rocky asteroids, only about 20 percent of the grains was exposed to solar cosmic ray ions. Results based on present-day conditions in the asteroid belt agree well with irradiation features observed in gas-rich meteorites. An origin during epochs of early solar system evolution is not required.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA. Washington Advan. in Planetary Geol.; p 1-218
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    Weathering of iron sulfides under Mars surface ambient conditions (1981)
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    Publication Date: 2011-08-18
    Description: The study of iron sulfide surface alternation reactions under Mars' surface ambient conditions begun during 1980 was extended through improved irradiation design and experimental protocols. A wider range of humidities and more intense irradiation were incorporated in the study. X-ray photoelectron spectra of irradiated chips suggest formation of FeSO4, FeCO3, and an iron oxide on the iron sulfide substrates studied.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Houston Univ. The 1981 NASA ASEE Summer Fac. Fellowship Program, Vol. 1; 28 p
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  • 58
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    Derivation of the collision probability between orbiting objects The lifetimes of Jupiter's outer moons (1981)
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    Publication Date: 2011-08-18
    Description: A general form is derived for Opik's equations relating to the probability of collision between two orbiting objects to their orbital elements, and used to determine the collisional lifetime of the eight outer moons of Jupiter. The derivation is based on a concept of spatial density, or average number of objects found in a unit volume, and results in a set of equations that are easily applied to a variety of orbital collision problems. When applied to the outer satellites, which are all in irregular orbits, the equations predict a relatively long collisional lifetime for the four retrograde moons (about 270 billon years on the average) and a shorter time for the four posigrade moons (0.9 billion years). This short time is suggestive of a past collision history, and may account for the orbiting dust detected by Pioneers 10 and 11.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 48; Oct. 198
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  • 59
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    Volcanism on Mars (1981)
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    Publication Date: 2011-08-18
    Description: In situ chemical analyses of Martian soil by the Viking lander indicate mafic to ultramafic source rocks, consistent with both remote sensing data indicating the presence of pyroxene and olivine and with petrologic modeling which suggests that Martian lavas are iron-rich and ultramafic. Photogeological analysis of the Martian surface reveals two types of volcanic morphology: (1) central volcanoes, developed by continued and prolonged eruption from a point source vent; and (2) volcanic plains, recognized by mare ridges and flow lobes. When these volcanic morphologies are combined with relative age data, a volcanic history may be derived that is consistent with a moonlike thermal history involving a lithosphere of increasing thickness with time which gradually suppresses the volcanism.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Reviews of Geophysics and Space Physics; 19; Feb. 198
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  • 60
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    Turbulence in deep radio occultations (1981)
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    Publication Date: 2011-08-18
    Description: The effects of turbulence in the focal region of spherical or weakly oblate refracting bodies on the evolute flashes associated with the crossing of the evolute of the planetary limb by an occulted spacecraft are investigated. The approximate theory of focal evolutes in oblate refractivity fields developed by Eshleman et al. (1979) is combined with a generalized weak scattering scintillation theory that includes the effect of focusing around a curved limb to obtain expressions for the scintillation index and power spectrum. Results are then applied to the radio observations of the crossing of the focal evolute of Jupiter by Voyager 1, in which no flash was detected, and to the effects of the solar coronal plasma on the gravitational lens of the sun.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Radio Science; 16; Nov
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  • 61
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    Ground-based observations of the Jovian ring and inner satellites (1981)
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    Publication Date: 2011-08-18
    Description: Ground-based 0.9-micron observations of the Jovian ring and inner satellites are reported. The ring observations substantially confirm those obtained by the Voyager spacecraft. The first ground-based detection of 1979J2 suggests a geometric albedo of about 0.10 and a new value for its orbit period of 16 hr 11 min 23.5 + or - 0.5 sec.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 48; Dec. 198
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  • 62
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    Mars - Far-infrared spectra and thermal-emission models (1981)
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    Publication Date: 2011-08-18
    Description: Spectra of Mars from 100 to 360 kaysers were obtained during three different observation periods from NASA's Kuiper Airborne Observatory. Also, a new thermal model was constructed for the surface of Mars, and synthetic spectra were computed from the models to compare with the observations. The models include the effects of a dusty atmosphere which absorbs, scatters, and reradiates energy. The synthetic spectra show significant effects on disk-averaged brightness temperatures, as well as absorption features due to silicate dust. The spectra of Mars, which are ratios of Mars to the moon, do not fit the synthetic spectra unless the surface emissivities of Mars and the moon have different dependencies on wavelength. A possible explanation for this behavior is a difference in soil particle-size distributions between Mars and the moon, with Mars being depleted in large particles compared to the moon. Small particles are consistent with clay minerals which have been suggested elsewhere as constituents of the Martian surface.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 48; Nov. 198
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  • 63
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    Laboratory measurements of the microwave opacity of sulfur dioxide and other cloud-related gases under simulated conditions for the middle atmosphere of Venus (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 48; Nov. 198
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  • 64
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    Evidence for the acceleration of ionospheric O/+/ in the magnetosheath of Venus (1981)
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    Publication Date: 2011-08-18
    Description: Plasma spectra from 12 orbits of the Pioneer-Venus Orbiter are reported which suggest the presence of ionospheric material in the magnetosheath plasma near and sunward of the terminator plane. Each spectrum shows a high E/q peak, consistent with O(+) moving at a speed lower than or comparable to that of the ambient magnetosheath plasma. It is pointed out that even though the data set is limited, the most intense heavy-ion fluxes clearly occur at altitudes less than a few thousand km. With the identification of the energetic component at O(+), the data reveal a trend for the speed of O(+) near the planet to be lower than the local magnetosheath speed, whereas the two speeds are comparable at altitudes above a few thousand km. These data, in combination with related observations that indicate O(+) moving at ambient speed in the distant wake, suggest that ionospheric material is swept up by the magnetosheath, accelerated to ambient speed within a few thousand km, and carried back through the wake region.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters; 8; Dec. 198
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  • 65
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    Stability of goethite /alpha-FeOOH/ and lepidocrocite /gamma-FeOOH/ to dehydration by UV radiation - Implications for their occurrence on the Martian surface (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The geochemistry of the FeOOH polymorphs is an important consideration when evaluating the likelihood of an occurrence of detectable amounts of these minerals on Mars. An investigation is conducted regarding the stability of the FeOOH polymorphs geothite and lepidocrocite to dehydration in the presence of UV radiation. A thorough characterization of the FeOOH powders used in the laboratory experiments is presented, and the irradiational facility and experimental procedures are described. The results obtained in the conducted experiments are discussed. It is found that there is as yet no basis in laboratory experiments for inferring that perceptible UV photodehydration of FeOOH polymorphs will occur naturally on the surface of Mars on a time scale of at least 10-100 years.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Nov. 10
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  • 66
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    Unidentified features in the spectrum of Triton (1981)
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    Publication Date: 2011-08-18
    Description: Photometry at 3.5 microns was taken with the Infrared Telescope Facility of the Multiple Mirror Telescope to obtain an improved IR spectrum of Triton. The observations show features that are not in detailed agreeement with previous identifications of methane or methane frost, although the general spectral behavior leading to such identifications has been confirmed. It is believed that a combination of surface and atmospheric absorptions may resolve some discrepancies; for instance, many hydrated minerals and frosts which are dark between 3.0 and 4.0 microns may combine with a carbon monoxide atmosphere to yield the data in question.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 294; Nov. 5
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  • 67
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    Noble-gas-rich separates from the Allende meteorite (1981)
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    Publication Date: 2011-08-18
    Description: Predominantly carbonaceous HF/HCl-resistant residues from the Allende meteorite are studied. Samples are characterized by SEM/EDXA, X-ray diffraction, INAA, C, S, H, N, and noble gas analyses. Isotopic data for carbon show variations no greater than 5%, while isotopic data from noble gases confirm previously established systematics. Noble gas abundances correlate with those of C and N, and concomitant partial loss of C and normal trapped gas occur during treatments with oxidizing acids. HF/HCl demineralization of bulk meteorite results in similar fractional losses of C and trapped noble gases, which leads to the conclusion that various macromolecular carbonaceous substances serve as the main host phase for normal trapped noble gases and anomalous gases in acid-resistant residues, and as the carrier of the major part of trapped noble gases lost during HF/HCl demineralization. Limits on the possible abundances of dense mineralic host phases in the residues are obtained, and considerations of the nucleogenetic origin for CCF-XE indicate that carbonaceous host phases and various forms of organic matter in carbonaceous meteorites may have a presolar origin.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta; 45; Oct. 198
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    A source of plasma turbulence at the ionopause of Venus (1981)
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    Publication Date: 2011-08-18
    Description: The microscopic aspects of the interaction of the solar wind with the ionosphere of Venus are explored, in light of simultaneous suprathermal ion and low frequency electric field signal measurements by Pioneer Venus instruments which suggest that the two ionopause phenomena may be causally related. Both parallel and perpendicular propagating waves are examined for instability, in the presence of planetary ions added to the flowing ionosheath plasma, by linear Vlasov theory. While for the low beta plasma conditions of the ionopause neither electrostatic nor electromagnetic parallel propagating waves are found to be unstable, perpendicular propagating electrostatic waves are unstable and have the proper frequency-wavelength relation to be Doppler shifted into the observed 100-Hz channel.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Nov. 1
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  • 69
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    Quasi-periodic climatic changes on Mars and earth (1981)
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    Publication Date: 2011-08-18
    Description: Evidence of climatic changes on Mars and the earth due to geologic and astronomical variations is discussed. Finely striped ice-free bands in the Martian polar caps have been taken to indicate that long term variations in the orbit and axial tilt of Mars have precipitated these features at the rate of a mm/yr. Photogrammetric and photometric methods have contributed to measurements of the composition and depth of the Martian caps (14-46 m), and observations of higher solar energy absorption in the northern ice cap implies greater dust deposition in that region than on the south cap; however, the transport mechanisms are not well understood. Comparisons of earth and Martian climatic variations data are made, noting a lack of information on the age intervals of marine and nonmarine sediments on the earth. The possibilities of using quantitative data other than layer thickness to constrain climate models are discussed, and the slope or albedo of layers, or the spacing of polar undulations are suggested.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: EOS; 62; Nov. 10
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  • 70
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    Modulation of Venus ion densities associated with solar variations (1981)
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    Publication Date: 2011-08-18
    Description: The dayside ion concentrations in the Venus ionosphere obtained by the Pioneer Venus orbiter ion mass spectrometer exhibit a modulation corresponding to the 27-day solar variation. Comparisons were made of the amplitudes of modulation of CO(2(+), C(+), and O2(+), with the amplitudes of the 27-day variation in the 10.7-cm solar radio flux and the simultaneously measured EUV fluxes at He II (304 A) and Lyman-beta(1026 A), together with a theoretical analysis of the effects of solar variability on the ionosphere and neutral atmosphere of Venus. This analysis leads to the conclusion that the observed modulation of dayside ion densities is primarily due to the variability in the ionizing EUV radiations and, to a much lesser extent, the result of the variability with solar activity of the neutral atmosphere via the variability in exospheric temperature. In this connection, it is also shown theoretically why the percentage variation of exospheric temperature on Venus (as observed in the ONMS data) for a given variation in the 10.7-cm radio flux is only half of the exospheric temperature variation for earth.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters; 8; July 198
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  • 71
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    Sulfur dioxide and other cloud-related gases as the source of the microwave opacity of the middle atmosphere of Venus (1981)
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    Publication Date: 2011-08-18
    Description: Spacecraft radio occultation measurements imply the presence of a nonuniformly mixed gaseous absorber within, but mostly below, the main cloud layer of sulfuric acid-water droplets measured by Pioneer-Venus. Preliminary considerations of the amount, distribution, and effects of sulfur dioxide and other gases, which apparently are associated with and produce the cloud, indicate that they constitute an important, and probably the predominant, source of the observed microwave opacity of the middle atmosphere of Venus.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 46; Apr. 198
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    Titan (1981)
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    Publication Date: 2011-08-18
    Description: The paper reviews current knowledge about Titan's atmosphere, surface, interior, and nearby environment. An attempt is made to place the satellite's history within the context of the formation of the Saturn system and to describe possible evolutionary paths for its atmosphere and interior.
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    Diminished tektite ablation in the wake of a swarm (1981)
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    Publication Date: 2011-08-18
    Description: Observations of ablation markings on tektite surfaces reveal that a large variation in aerodynamic heating must have occurred among the members of a swarm during atmospheric entry. In a few cases, the existence of jagged features indicates that these tektite surfaces may have barely reached the melting temperature. Such an observation seems to be incompatible with the necessarily large heating rates suffered by other tektites which exhibit the ring wave melt flow. A reconciliation is proposed in the form of a wake shielding model which is a natural consequence of swarm entry. Calculations indicate that the observed ablation variations are actually possible for swarm entry at greater than escape velocity. This aerodynamic conclusion provides support for the arguments favoring extraterrestrial origin of tektites.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; June 10
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    Jupiter - Structure and composition of the upper atmosphere (1981)
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    Publication Date: 2011-08-18
    Description: The Voyager ultraviolet stellar occultation data yield a temperature of 200 + or - 50 K at about 400 km, and the solar occultation data give 1100 + or - 200 K at 1450 km above the ammonia cloud tops. The temperature gradient between 400 and 1450 km is approximately 1 K/km. The mesospheric temperature structure gives no strong indication of an earth-like mesopause. The heating of the upper atmosphere appears to result from a combination of magnetospheric charged particle precipitation, ion drag, inertia gravity waves, and solar EUV. The volume mixing ratios of CH4 and C2H6 at 325 km are measured to be 2.5(+3, -2) x 10 to the -5th and 2.5(+2.0, -1.5) x 10 to the -6th, respectively, which are lower than in the stratosphere. The C2H2 volume mixing ratio is not greater than 5 x 10 to the -6th at 300 km. The homopause value of the equatorial eddy diffusion coefficient is found to be 1-2 x 10 to the -6th sq cm/s.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal; vol. 247
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    New magnetic results from Allende C3/V/ (1981)
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    Publication Date: 2011-08-18
    Description: Thermomagnetic analyses of Allende C3(V) suggest that magnetic phases contributing about 15% to saturation magnetization with transition temperatures not greater than 320 C, also contribute about 90% to natural remanence (NRM) and about 80% to the saturation isothermal remanence (SIRM). Phases carrying the dominating part of of the NRM are found to be intergrown, magnetically interacting, and thermally unstable, beginning at temperatures as low as 50 C. The ratio of the NRM/SIRM ranges from 0.004 to 0.006 for the bulk meteorite and from 0.0004 to 0.005 for chondrules of all sizes. The remanent coercive force behavior suggests coexisting magnetic phases with differing Curie points or with the low temperature transitions being due to transformation of a thermally metastable phase.
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    Solar wind origin of Ar-36 on Venus (1981)
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    Publication Date: 2011-08-18
    Description: An examination is conducted concerning the circumstances under which the difference between earth and Venus (and Mars) fits naturally into theories in which the terrestrial planets formed by the gradual sweeping up of planetesimals in an essentially gas-free protoplanetary swarm. The primary purpose of the reported investigation is to use observational data to define restrictions on planetary formation theories that would be imposed if most of Venus' inert gases come from the solar wind. The observational data support the suggestion that the abundances of Ar, Kr, and Xe on Venus have been augmented by a component of solar composition. Solar wind implantation at an early stage of accumulation provides a natural way of producing the observed extreme heliocentric distribution of this component, provided that accumulation occurred after dissipation of solar gas from the solar nebula
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 46; Apr. 198
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    Thermal response of Saturn's ring particles during and after eclipse (1981)
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    Publication Date: 2011-08-18
    Description: The investigation is based on data which were obtained on May 18, 1978, at the 5-m Hale telescope on Palomar Mountain. A Ge:Ga bolometer was used at the f/70 Gregorian focus; a cold interference filter limited the wavelength response to between 16 and 26 micrometers. A brightness asymmetry is observed between the ansae of all three rings; the largest asymmetry occurs in the C ring. The simplest explanation of such asymmetries is just the eclipse cooling and subsequent heating of similar particles at different radial distances from Saturn, coupled with the different travel times from eclipse exit to east ansa. The observed eclipse cooling and subsequent heating in Saturn's B ring support the idea that the uppermost surface of the particles is of low-conductivity water frost, similar to the uppermost surface of the Galilean satellites (omitting Io).
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 46; Apr. 198
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    The magnetic field of Jupiter - A generalized inverse approach (1981)
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    Publication Date: 2011-08-18
    Description: The estimation of planetary magnetic fields from observations of the magnetic field gathered along a spacecraft flyby trajectory is examined with the aid of generalized inverse techniques, with application to the internal magnetic field of Jupiter. Model non-uniqueness resulting from the limited spatial extent of the observations and noise on the data is explored and quantitative estimates of the model parameter resolution are found. The presence of a substantial magnetic field of external origin due to the currents flowing in the Jovian magnetodisc is found to be an important source of error in estimates of the internal Jovian field, and new models explicitly incorporating these currents are proposed. New internal field models are derived using the vector helium magnetometer observations and the high field fluxgate observations of Pioneer 11, and knowledge of the external current system gained from the Pioneer 10 and Voyagers 1 and 2 encounters.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Sept. 1
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    Comment on 'Azimuthal magnetic field at Jupiter' by J. L. Parish, C. K. Goertz, and M. F. Thomsen (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: In the first paper, an alternative to one of the models of current flow giving rise to the azimuthal component of the Jupiter magnetic field considered by Parish et al. (1980) is proposed which takes into account the magnetic fields due to return currents and is consistent with Pioneer 10 observations. In the present model, currents enter the equatorial sheet at both poles and then flow radially outward, with a total current flowing into the polar regions of about 1.4 x 10 to the 8th A. In the reply, it is contended that, although the return currents must be present, their net effects almost exactly cancel and their contributions to the near-equatorial field may be neglected for regions sufficiently far from the field lines on which the return current flows. Furthermore, the difference in the total currents estimated by Parish et al. and in the first paper is attributed to the uncertainties and inadequacy of the fit of either model to the observations and to a difference in mathematic expressions used for the field rather than a significant difference between models.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Sept. 1
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  • 80
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    Partition coefficients for REE between garnets and liquids - Implications of non-Henry's Law behaviour for models of basalt origin and evolution (1981)
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    Publication Date: 2011-08-18
    Description: An experimental investigation of Ce, Sm and Tm rare earth element (REE) partition coefficients between coexisting garnets (both natural and synthetic) and hydrous liquids shows that Henry's Law may not be obeyed over a range of REE concentrations of geological relevance. Systematic differences between the three REE and the two garnet compositions may be explained in terms of the differences between REE ionic radii and those of the dodecahedral site into which they substitute, substantiating the Harrison and Wood (1980) model of altervalent substitution. Model calculations demonstrate that significant variation can occur in the rare earth contents of melts produced from a garnet lherzolite, if Henry's Law partition coefficients do not apply for the garnet phase.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta; 45; Sept
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  • 81
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    Polygon patterns on Europa (1981)
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    Publication Date: 2011-08-18
    Description: The formation of polygon patterns in the development of crack networks in cooling basalt flows and similar contracting systems, and under natural conditions in an essentially unbounded basalt flow, are analyzed, and the characteristics of hexagonal and pentagonal patterns in isotropic stress fields are discussed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 291; May 28-J
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    Pioneer fly-by of Saturn and its rings (1981)
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    Publication Date: 2011-08-18
    Description: Results acquired by the imaging photopolarimeter on board Pioneer 11 during the spacecraft fly-by of Saturn and its rings on September 1, 1979 are reviewed. Analysis of the broadband photometry and polarimetry obtained of the Saturn atmosphere has been used to determine a cloud top height of 300 mb and a scale height of the aerosol distribution about 1/4 that of the ambient gas, and to point out differences between the forward scattering and belt and zone characteristics of the Saturn and Jupiter atmospheres. Images of Saturn's rings have been used to derive a profile of ring optical depth between 1.22 and 2.35 Saturn radii, and reveal new divisions and thin rings and azimuthal variations in the brightness of the A ring not observable from earth. Linear polarization observations of Titan in red and blue light reveal that the aerosols near the top of the atmosphere have radii less than about 0.09 micron and that the optical thickness of the small aerosol layer is about 0.6 above an effectively depolarizing surface, and indicate radii of 2845 + or - 25 km and 2880 + or - 22 km in red and blue light, respectively. Earth-based and spacecraft data are consistent with the formation of rings structures as a result of Poynting-Robertson drag and gravitational satellite resonances with the original ice and rock particles.
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    Upper atmosphere of Jupiter - A post Voyager perspective (1981)
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    Publication Date: 2011-08-18
    Description: Some significant upper atmosphere features of Jupiter are discussed with reference to the Voyager observations of 1979. From the time of Pioneer observations in 1973-1974, the Jovian upper atmospheric temperature has increased by about 30%, the eddy diffusion coefficient at the homopause decreased by a factor of 100, the equatorial disk Lyman alpha intensity increased by a factor of 30, and the equatorial ionosphere became more extensive and showed diurnal variation. Important potential candidates for upper atmosphere energetics are thought to be the penetration of the magnetospheric soft electrons, Joule heating mechanism, and auroral electrons.
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    The development of future lunar exploration (1981)
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    Publication Date: 2011-08-18
    Description: Selected aspects of the eventual development of lunar exploration leading to the establishment of a human outpost on the moon are discussed. Possible means of spacecraft propulsion and guidance on an earth-moon trajectory are examined, together with likely means of telecommunications, including by laser and lunar-orbiting communications satellites. As yet unexploited orbits in the earth-moon system are pointed out, and the necessity for the increased use of computerized robots for surface navigation is discussed. Favorable locations for a habitat site, particularly the lunar poles are also considered. Implications of the availability of extraterrestrial resources for materials processing techniques and food production in the lunar environment are then indicated.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: vol. 34; Jan. 198
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  • 85
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    The DSN radio science system (1981)
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    Publication Date: 2011-08-18
    Description: The Radio Science experiments at Voyager 1 Saturn encounter which included two atmospheric occultations, a planetary ring occultation, and ring scattering experiment were supported by Deep Space Stations in Australia (DSS 43) and Spain (DSS 63). The DSN Radio Science System data flow from receipt of the radio signals at the antenna to delivery of the recorded data to the project are described.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: The Telecommun. and Data Acquisition; p 89-93
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  • 86
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    Formation of organic molecules on Titan (1981)
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    Publication Date: 2011-08-18
    Description: A mechanism is proposed for the formation of complex organic nitrogen compounds in the dense lower atmosphere of Titan. The mechanism is based on three-body association reactions with HCNH(+) ions formed by the reaction of N(+) with CH4, which lead to the production of ethyl cyanide, vinyl cyanide and cyanoacetylene. Calculations for a model atmosphere consistent with the preliminary interpretation of Voyager 1 data for the region of maximum cosmic ray activated chemistry, corresponding to a temperature between 150 and 160 K and a pressure of 20 mbar, are presented which show substantial organic nitrile and hydrogen cyanide production rates. Based on these production rates, it is expected that significant equilibrium concentrations of these compounds will be found on Titan.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 293; Sept. 3
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  • 87
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    Anomalous C-12H4:C-13H4 strengths in 3 ny sub 3 (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The C-12:C-13 ratios in the atmospheres of the outer planets are important parameters with which to test models for isotope formation and fractionation during the early history of the solar system, yielding insight into processes occurring in the primitive solar nebula. The 3 ny sub 3 spectra of methane were obtained using the Kitt Peak Solar Fourier Transform Spectrometer and a 6 m White cell. The experimental results are summarized in a table. The strength ratios for the R-branch of 3 ny sub 3 exhibit strong anomalies, with C-13H4 lines consistently weaker than their C-12H4 counterparts. The C-12:C-13 abundance ratios for the atmospheres of Jupiter and Saturn have been redetermined using the 3 ny sub 3 line-strength ratios measured.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal; vol. 247
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  • 88
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    Asteroidal agglutinate formation and implications for asteroidal surfaces (1981)
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    Publication Date: 2011-08-18
    Description: The possible role of spallation on the free surfaces of target bodies in asteroid surface evolution in the presence of colliding bodies is considered. The ease of impact melt formation is discussed based on the results of shock recovery experiments, and a difference between collisions with dense, nonporous targets and with porous, particulate powders is demonstrated. It is shown that agglutinate-type glasses can be produced at impact velocities of 5 km/sec, but only in highly comminuted, porous targets and not in dense rocks. The apparent lack of agglutinate-type glasses on asteroid surfaces is explained in terms of coarse-grained asteroidal surfaces acting as dense, nonporous bedrock. It is argued that a possible mechanism inhibiting asteroidal surface comminution so as to inhibit melt formation and the effects of micrometeoroid impacts can be represented by collision processes with finite-sized targets rather than with a semi-infinite half-space as in the case of the moon, which give rise to spallation products rather than crater ejecta.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 46; June 198
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  • 89
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    Saturn's magnetic tail - Structure and dynamics (1981)
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    Publication Date: 2011-08-18
    Description: Voyager 1 magnetic field observations have provided evidence of a Saturnian magnetic tail. Tail current system distributions are inferred through comparison of the observations with a realistic magnetotail current system model. Temporal variations observed in the tail were probably produced by solar wind variations.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 292; Aug. 20
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  • 90
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    Surface waves on Saturn's magnetopause (1981)
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    Publication Date: 2011-08-18
    Description: Voyager 1 magnetometer data have shown that small-amplitude surface waves occurred on Saturn's dayside magnetopause, causing multiple inbound crossings of this boundary. These waves were travelling approximately parallel to Saturn's equatorial plane along the magnetopause ('tailward'), suggesting that they were driven by the rotation of Saturn's magnetosphere. Hydromagnetic waves (possibly slow mode) were observed in the adjacent magnetosheath.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 292; Aug. 20
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  • 91
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    Saturn's kilometric radiation - Satellite modulation (1981)
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    Publication Date: 2011-08-18
    Description: There is an episodic 66-h modulation of the Saturn kilometric radiation which is both frequency and Dione-phase dependent. The behavior is significantly different from the way in which Io modulates the Jovian emission.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 292; Aug. 20
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  • 92
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    Saturnian kilometric radiation - Statistical properties and beam geometry (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: An adequate description of the average statistical properties of Saturn's radio emissions is needed for a study of these emissions. Data regarding these properties are presented, and the implications for source location, beaming, and magnetic surface anomalies are discussed. A description is presented of the average properties of the Saturn kilometric radiation (SKR) as observed from two locations by the Voyager 1 planetary radio astronomy (PRA) instrument for a 2-month period centered on the November 12, 1980 encounter. An analysis of the occurrence pattern of SKR as a function of Saturn's rotation phase has shown that SKR occurrence is not continuous, but variable and roughly periodic. The statistical SKR properties obtained strongly constrain possible source locations. Several source locations are possible, but most intriguing is the region at high latitudes near the noon meridian.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 292; Aug. 20
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  • 93
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    Arc structure in Saturn's radio dynamic spectra (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: It is pointed out that one of the most spectacular findings of the Voyager 1 planetary radio astronomy experiment (PRA) was the discovery of nested arc-like structures in the dynamic spectra of Jupiter's decametric emission. These arcs have curvature in either a direction towards increasing or decreasing time. Similar arc structures are also evident in Saturn kilometric radiation. These structures appear superimposed on the strong intensity modulation which is controlled by the rotation of the planet and on fast and narrow band fluctuations which give a very large variability to the PRA observations on a 6-s, 20-kHz scale. The characteristics of the arcs are examined and compared with the arc structure in Jupiter. The similarities between Saturn's and Jupiter's arc structures are found to imply that they are probably due to the same physical mechanism.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 292; Aug. 20
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  • 94
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    Saturn's ring current and inner magnetosphere (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The Voyager 1 magnetic field observations at Saturn are shown in a graph. The departure of the oberved magnetic field from the field of a dipole is considered. The observed field magnitude is appreciable less than that of the model dipole at small radial distances and greater than the model dipole in the more distant magnetosphere. These characteristics can be understood by introducing a model current system similar to a system originally applied to observations of the Jovian magnetic disk. Saturn's ring current has important implications for charged-particle motion in Saturn's magnetosphere, particularly the absorption of trapped radiation by its many satellites and rings. The absorption signature observed by the Voyager 1 cosmic ray experiment near the orbital position of Rhea illustrates well the effects of Saturn's ring current on charged particle trajectories.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 292; Aug. 20
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  • 95
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    Topology of Saturn's main magnetic field (1981)
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    Publication Date: 2011-08-18
    Description: The reported analysis of Saturn's main magnetic field takes into account the data obtained by Voyager 1 during its close flyby of Saturn in November 1980. A magnetic field model for the analysis of Saturn's main field in which the distributed ring currents are explicitly modelled is constructed. The considered internal field parameters constitute a first approximation to Saturn's main field. Several model current systems that might be expected on physical grounds to be active in Saturn's magnetosphere are considered. It is pointed out that certain aspects of Saturn's main magnetic field relevant to the planet's interior have been discussed by Stevenson (1980). In particular, the unexpectedly small dipole moment seems to be consistent with the gravitational settling of helium, which leads to a much smaller electrically conducting and convecting region than would be expected of a homogeneous distribution of hydrogen and helium.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 292; Aug. 20
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  • 96
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    Low-frequency plasma waves near Saturn (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Voyager planetary radio astronomy observations of low frequency emissions detected around the time of closest approach to Saturn and near the outbound ring plane crossing are presented. Near the ring plane an electron density of between 5 and 20 electrons/cu cm at dista
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 292; Aug. 20
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  • 97
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    Impulsive radio discharges near Saturn (1981)
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    Publication Date: 2011-08-18
    Description: Nonthermal radio emissions from the Saturn system were first detected by the Voyager planetary radio astronomy (PRA) experiment on board Voyager 1 in January 1980. Since then emission between 100 kHz and 1 MHz from the planet, termed Saturn kilometric radiation (SKR), has been received almost continuously. A description is presented of eight characteristics which have been fairly well defined by the Voyager 1 encounter. These include a very flat broadband frequency spectrum, a period of approximately 10 h 10 min, a change in the envelope shape of episodes between pre and postencounter, an intensity population structure typical of plural populations, and an episodic structure of a width of approximately 180 deg. It was found that postencounter episodes continue for about three times as long as preencounter ones, and that postencounter bursts are left-circularly polarized at high frequencies. At least one episode shows the onset of high frequency events some time before that of lower frequency ones.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 292; Aug. 20
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  • 98
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    Distribution of neutral gas and dust near Saturn (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The distribution of neutral gas and dust within the magnetosphere of Saturn has been inferred from the electron velocity distribution functions measured by the Voyager 1 plasma science experiment. Substantial enhancements of neutral material near Titan and in the vicinity of Enceladus are found. The E ring is also shown to be larger than previously thought.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 292; Aug. 20
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  • 99
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    Titan's atmosphere - Temperature and dynamics (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: In the lower atmosphere of Titan IR brightness temperatures exhibit meridional contrast less than approximately 3 K. Seasonal variations are absent because of the large radiative time constant. In the upper stratosphere meridional contrasts are approximately 20 K, consistent with 100 m/s cyclostrophic zonal winds, and the radiative time constant is short, implying a large seasonal variation in the temperature and wind field. The absence of longitudinal thermal structure implies that zonally symmetric flows effect the meridional transport of heat. A simple model yields meridional velocities approximately 0.04 cm/s and vertical eddy viscosities approximately 1,000 sq cm/s in the lower troposphere, and meridional velocities approximately 5 cm/s in the upper stratosphere.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 292; Aug. 20
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  • 100
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    Mean molecular weight and hydrogen abundance of Titan's atmosphere (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The 200-600/cm continuum opacity in the troposphere and lower stratosphere of Titan is inferred from thermal emission spectra from the Voyager 1 IR spectrometer (IRIS). The surface temperature and mean molecular weight are between 94 and 97 K and between 28.3 and 29.2 AMU, respectively. The mole fraction of molecular hydrogen is 0.002 + or - 0.001, which is equivalent to an abundance of approximately 0.2 + or - 0.1 km amagat.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 292; Aug. 20
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