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  • LUNAR AND PLANETARY EXPLORATION  (1,076)
  • 1995-1999
  • 1990-1994  (1,076)
  • 1999
  • 1992  (1,076)
Collection
Keywords
Years
  • 1995-1999
  • 1990-1994  (1,076)
Year
  • 1
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    A spatial domain Stokes flow model for the gravity and topography of the middle latitudes of Venus (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A novel modeling technique is developed and applied to the long-wavelength gravity, topography, and internal density structure of Venus. The focus of this study is to employ data on the gravity and topography of Venus, which are obtained from the Pioneer Venus Orbiter mission, to enhance understanding some key aspects of the internal structure of the planet. A modeling strategy utilizing 'stokeslets' or basic units of slow viscous flow (governed by the Stokes equations) to duplicate the observed gravity and topography is implemented.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; E11; p. 18,285-18,294.
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  • 2
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    An analysis of the focusing performance of Magellan SAR image data (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Synthetic aperture radar (SAR) focusing can be achieved either based on accurate ephemeris data or on an autofocusing process. For the Magellan project, such a decision must be made in the early phase of Magellan SAR system design. The analysis of the emphemeris requirement is complicated. The analysis given by the author leads to the conclusion that empheris data obtained from the Magellan navigation system provide sufficient accuracy to meet the Magellan image resolution requirement.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: IGARSS '92; Proceedings of the 12th Annual International Geoscience and Remote Sensing Symposium, Houston, TX, May 26-29, 1992. Vol. 1 (A93-47551 20-43); p. 610-613.
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  • 3
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    Origin and use of Martian nomenclature (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The history and construction of Martian place names are examined. The 24 specific descriptor terms in use for Mars are defined. Informal names of individual rocks are discussed: the human fondness for informality is evident in the names attached to individual rocks at the Viking Lander sites.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 1305-1314.
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  • 4
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    SAR data processing for the Magellan prime mission (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Magellan prime mission involves mapping the planet of Venus once around its rotational axis. The Magellan synthetic aperture radar (SAR) data processing facility processes all SAR data collected by the Magellan spacecraft into image data on an orbit-by-orbit basis. About 1700 million bits of radar data were collected. A complete description of the Magellan SAR Data Processing Facility is provided with emphasis on key design features of the data processors that satisfied the project data processing requirements. A summary of the attained data processing performance is included, as well as a brief discussion of some of the constraints and considerations regarding the applicability of the processors to meeting the data processing goals anticipated for the follow-on mission phases (i.e., cycles II, III, and beyond).
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: IGARSS '92; Proceedings of the 12th Annual International Geoscience and Remote Sensing Symposium, Houston, TX, May 26-29, 1992. Vol. 1 (A93-47551 20-43); p. 606-609.
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  • 5
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    Geodesy and cartography of the Martian satellites (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The difficulties connected with conventional maps of Phobos and Deimos are largely overcome by producing maps in digital forms, i.e., by projecting Viking Orbiter images onto a global topographic model made from collections of radii derived by photogrammetry. The resulting digital mosaics are then formatted as arrays of body-centered latitudes, longitudes, radii, and brightness values of Viking Orbiter images. The Phobos mapping described was done with Viking Orbiter data. Significant new coverage was obtained by the Soviet Phobos mission. The mapping of Deimos is in progress, using the techniques developed for Phobos.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 1249-1256.
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  • 6
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    Physical and chemical weathering (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Physical and chemical weathering processes that might be important on Mars are reviewed, and the limited observations, including relevant Viking results and laboratory simulations, are summarized. Physical weathering may have included rock splitting through growth of ice, salt or secondary silicate crystals in voids. Chemical weathering probably involved reactions of minerals with water, oxygen, and carbon dioxide, although predicted products vary sensitively with the abundance and physical form postulated for the water. On the basis of kinetics data for hydration of rock glass on earth, the fate of weathering-rind formation on glass-bearing Martian volcanic rocks is tentatively estimated to have been on the order of 0.1 to 4.5 cm/Gyr; lower rates would be expected for crystalline rocks.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 626-651.
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  • 7
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    Long-term orbital and spin dynamics of Mars (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: This review of the long-term dynamical behavior of Mars covers secular variations of the orbit, oscillations of the obliquity, and polar wandering. Calculations of the large-scale obliquity oscillations of Mars are updated using the most recent orbit theory and contrasted with the earth. The motion for Mars is characterized by about 100,000-yr oscillations driven by differential spin axis and orbit plane precession rates during which the obliquity may change by as much as about 20 deg. The possible role of spin-orbit secular resonances to the spin axis histories of the earth and Mars is also considered. Numerical integrations of the equations of motion indicate that Mars may have passed through resonance as little as 5 Myr ago and that obliquities approaching about 45 deg could have been achieved during such an event.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 298-320.
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  • 8
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    Stress and tectonics on Mars (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Deformation of the Martian lithosphere and the various theoretical formulations used to model its behavior on local, regional, and global scales are studied. An overview of the various classes of tectonic features found on Mars is presented. The tectonic record on Mars, which provides the basic framework for interpreting theoretical thermomechanical models in terms of major tectonic events and provinces is summarized. The thickness of the elastic lithosphere is estimated using its response to local surface loads, and significant spatial variability is found, with values ranging from 20 to 300 km. A comparison of the major radial graben systems with theoretical stress models shows that more than one mechanism of lithospheric deformation is required to produce its enormous extent.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 249-297.
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  • 9
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    Gravity and topography (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The paper summarizes the fundamental gravity field constants for Mars and a brief historical review of early determinations and current-day accurate estimates. These include the planetary gravitational constant, global figure, dynamical oblateness, mean density, and rotational period. Topographic results from data acquired from the 1967 opposition to the most recent, 1988, opposition are presented. Both global and selected local topographic variations and features are discussed. The inertia tensor and the nonhydrostatic component of Mars are examined in detail. The dimensionless moment of inertia about the rotational axis is 0.4 for a body of uniform density and 0.37621 if Mars were in hydrostatic equilibrium. By comparing models of both gravity and topography, inferences are made about the degree and depth of compensation in the interior and stresses in the lithosphere.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 209-248.
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  • 10
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    Spacecraft exploration of Mars (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Soviet and American spacecraft exploration of Mars over the past quarter century is reviewed. Data on the earliest Soviet attempts to send spacecraft to observe the planet are presented. Of the series of spacecraft that were announced (designated Mars 1 to Mars 7), none fulfilled all its scientific goals, but some good photographs and other important data were obtained. Of the six spacecraft in the Mariner series, two failed, but Mariner 4 first revealed the cratered surface of Mars, and Mariner 9 discovered all the major geologic features. The Viking mission, with its two Orbiters, two Landers, and its 6-yr duration, surpassed in quantity and variety of data all other missions combined. The Phobos mission ended in two failures, but the second of the two spacecraft acquired significant new data about Mars and Phobos. An appendix listing special issues of journals containing collections of papers about Mars is provided.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 71-119.
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  • 11
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    The planet Mars - From antiquity to the present (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Telescopic observations of Mars, from those of Galileo in 1610 to the late 19th century, were summarized by Flammarion (1892, 1909). Major compilations of knowledge of Mars were produced by Antoniadi (1930) and de Vaucouleurs (1954). Polar cap composition was debated until the discovery by the Viking mission that the north and south perennial polar caps are composed of different materials. Spacecraft data indicate a rich and diverse geologic history as well as many unsolved puzzles. An annotated list of books about Mars is provided. Basic physical and chemical data on Mars are summarized in tabular form, and a guide to the Martian seasons is given.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 1-33.
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  • 12
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    SAR data processing adaptation for Magellan Cycle II (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The authors describe the effort made at the Magellan SAR Data Processing Facility in adapting existing data processors to handle data collected from various imaging experiments. The different data processing requirements imposed by the various types of data are discussed, the tradeoffs and compromises made to work within the constraint of the existing systems are explained, and summary processing results obtained to date are given.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: IGARSS '92; Proceedings of the 12th Annual International Geoscience and Remote Sensing Symposium, Houston, TX, May 26-29, 1992. Vol. 1 (A93-47551 20-43); p. 100-103.
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  • 13
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    Remote radio observations of solar wind parameters upstream of planetary bow shocks (1992)
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    Publication Date: 2011-08-24
    Description: Radio emission is frequently produced at twice the electron plasma frequency 2fp in the foreshock region upstream of the terrestrial bow shock. Observations of this emission provide a remote diagnostic of solar wind parameters in the foreshock. Using ISEE-3 radio data, we present the first evidence that the radio intensity is proportional to the kinetic energy flux and to other parameters correlated with solar wind density. We provide a qualitative explanation of this intensity behavior and predict the detection of similar emission at Jupiter by the Ulysses spacecraft.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Solar Wind Seven; Proceedings of the 3rd COSPAR Colloquium, Goslar, Germany, Sept. 16-20, 1991 (A93-33554 13-92); p. 647-650.
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  • 14
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    Quasi-periodic climate change on Mars (1992)
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    Publication Date: 2011-08-24
    Description: The paper examines evidence that the Martian climate undergoes quasi-periodic variations, including the polar layered terrain, differences between the residual polar caps, and the current net southward flow of H2O. The driving functions for these variations are oscillations in the elements of the Martian orbit coupled with precession of the Martian spin axis. These 'astronomic variations' control the distribution of the insolation, which in turn influences the partition of volatiles between atmospheric and surface reservoirs. The major effects anticipated at low obliquity are growth of the polar caps, substantial decrease in surface pressure, cessation of duststorms, release of CO2 from the regolith, and poleward migration of H2O ground ice. At high obliquity, the mass of the perennial polar caps decreases and permanent CO2 frost disappears, CO2 desorbs from the regolith at high latitudes, the surface pressure may increase to several times its current value, and the atmospheric dust load increases.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 1180-1218.
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  • 15
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    Comparative aspects of the climate of Mars - An introduction to the current atmosphere (1992)
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    Publication Date: 2011-08-24
    Description: The study reviews the historical perspective of the Martian climate, beginning with the early view of inexorable climate change on an older, but otherwise very earthlike, planet and continuing through the period when earth-based spectroscopy and the Mariner 4, 6, and 7 flyby missions portrayed a moonlike body, heavily cratered and almost airless by comparison with earth. The most general features of the earth and Mars are discussed and compared, with consideration given to the standard atmospheres, atmospheric circulation, seasonal cycles of carbon dioxide, water, and dust, and coupling between cycles.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 799-817.
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  • 16
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    Radar determination of Mars surface properties (1992)
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    Publication Date: 2011-08-24
    Description: Radar studies of Mars have provided measurements of surface texture on scales of centimeters to hundreds of meters and measurements of surface material properties. Texture (rms surface tilts and estimates of small-scale roughness) may be inferred from dispersion and/or polarization of the radar echo; material properties (reflectivity of dielectric constant) are derived from echo strength. Mars is a diverse target; depending on location, rms surface tilts have been found to vary over the range 0.25 to 10 deg while reflectivity covers at least 3 to 13 percent. Plains units are the most variable, having both the smoothest and roughest surfaces, cratered terrain can be considered predictable and 'average' by comparison. Recent data identify scattering by small structures (perhaps rocks on or near the surface) as playing a more important role than previously recognized. Scattering by the residual ice cap near Mars' south pole is particularly unusual. The present state of radar surface studies is summarized.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 652-685.
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  • 17
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    Implementation and performance of the Magellan digital correlator subsystem (1992)
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    Publication Date: 2011-08-24
    Description: The Magellan synthetic aperture radar (SAR) produces Venus surface images from data collected by the SAR carried on board the Magellan spacecraft. The core of the primary Magellan SAR processor is the digital correlator subsystem (DCS). The pipeline DSC architecture enables the Magellan primary SAR processor (PSP) to achieve real-time data processing capability. The implementation and performance of the DSC are described. Hardware (H/W) constraints that influenced the processing algorithm design are highlighted.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: IGARSS '92; Proceedings of the 12th Annual International Geoscience and Remote Sensing Symposium, Houston, TX, May 26-29, 1992. Vol. 2 (A93-47551 20-43); p. 1301-1304.
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  • 18
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    Refinement of Magellan radiometric correction using range centroid estimation (1992)
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    Publication Date: 2011-08-24
    Description: The Magellan (MGN) synthetic aperture radar (SAR) processing radiometric compensation algorithm is described, and the effective pointing error caused by the terrain is examined. It is shown how the range centroid can be computed from spacecraft ancillary data with an accurate topographic model. In cases where such data are not available, a technique is presented to estimate the range centroid from the coherent radar echoes. This technique is demonstrated using MGN SAR data.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: IGARSS '92; Proceedings of the 12th Annual International Geoscience and Remote Sensing Symposium, Houston, TX, May 26-29, 1992. Vol. 2 (A93-47551 20-43); p. 1167-1170.
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  • 19
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    Radar mapping of Mercury - Full-disk images and polar anomalies (1992)
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    Publication Date: 2011-08-24
    Description: A random-code technique has been used at Arecibo to obtain delay-Doppler radar images of the full disk of Mercury. Anomalously bright features were found at the north and south poles. The north polar feature is oblong (4 by 8 deg) and offset from the pole. The smaller south polar feature is mostly confined to the floor of the crater Chao Meng-Fu. The polar locations and radar properties of these features indicate that they may be produced by volume scattering in ice. The images also reveal a variety of more subdued reflectivity features ranging in size from hundreds to thousands of kilometers; some of these appear to have an impact origin.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 258; 5082; p. 640-643.
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  • 20
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    Surface chemistry and mineralogy (1992)
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    Publication Date: 2011-08-24
    Description: The accumulated knowledge on the chemistry and mineralogy of Martian surface materials is reviewed. Pertinent information obtained by direct analyses of the soil on Mars by the Viking Landers, by remote sensing of Mars from flyby and orbiting spacecraft, by telescopic observations from earth, and through detailed analyses of the SNC meteorites presumed to be Martian rocks are summarized and analyzed. A compositional model for Mars soil, giving selected average elemental concentrations of major and trace elements, is suggested. It is proposed that the fine surface materials on Mars are a multicomponent mixture of weathered and nonweathered minerals. Smectite clays, silicate mineraloids similar to palagonite, and scapolite are suggested as possible major candidate components among the weathered minerals.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 594-625.
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  • 21
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    Cosmogenic nuclides in core samples of the Chico L6 chondrite - Evidence for irradiation under high shielding (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Results are presented from an analysis of core samples obtained from different depths of the Chico (New Mexico) L6 chondrite for various cosmogenic nuclides (Be-10, Al-26, and stable isotopes of He, Ne, and Ar). The relationships between the measured abundances of cosmogenic nuclides and cosmogenic Ne-22/Ne-21 ratio were compared with predictions of recent semiempirical models of Graf et al. (1990) and Reedy (1991), and it was found that both models closely reproduce the observed trends and absolute values of the data obtained. Noble gas data indicate that Chico experienced shielding similar to that of Jilin and greater than those of the Knyahinya or the Keyes chondrites. The exposure history for Chico is discussed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Meteoritics (ISSN 0026-1114); 27; 4; p. 371-381.
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  • 22
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    Dissemination and fractionation of projectile materials in the impact melts from Wabar Crater, Saudi Arabia (1992)
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    Publication Date: 2011-08-24
    Description: Results are presented from the analyses of small ballistically dispersed melt samples (occurring in the form of aerodynamically shaped spheres, dumbbells, and teardrops) from the Wabar Crater (Saudi Arabia) and of melts from the Wabar and Nejed meteorites. On the basis of the data obtained and of models for crater forming processes it is concluded that the ballistically-dispersed glasses were formed from material at shallow levels in the target zone where temperatures were higher and where intimate physical contact with the disrupting impactor was achieved. Siderophile element fractionation was completed early, while the impactor was undergoing decompression and prior to mixing with the target glasses.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Meteoritics (ISSN 0026-1114); 27; 4; p. 361-370.
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  • 23
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    Maintenance of strong rotational winds in Venus' middle atmosphere by thermal tides (1992)
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    Publication Date: 2011-08-24
    Description: The cloud-level atmosphere of Venus takes little more than four days to complete one rotation, whereas the solid planet below has a 243-day period. Computer simulations of the circulation of the Venus middle atmosphere between 40 and 85 kilometers, as driven by solar radiation absorbed in the clouds, reproduce (1) the observed cloud-level rotation rate, (2) strong vertical shears above and below the cloud tops, and (3) midlatitude jets and strong poleward flow on the day side. Simulated circulations converge to yield nearly the same zonal winds when initialized with both stronger or weaker rotation rates. These results support the hypothesis that the observed cloud-top rotation rate is maintained by statistical balance between fluxes of momentum by thermal tides and momentum advection by mean meridional circulation.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 257; 5070,; 647-650
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  • 24
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    Asteroid 951 Gaspra - Pre-Galileo physical model (1992)
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    Publication Date: 2011-08-24
    Description: An effort is made to derive from Galileo's 1991 encounter of the S-type asteroid 951 Gaspra general lessons that will be applicable to prospective earth-based observations of other asteroids. Attention is accordingly given to the derivation of spin-vector and shape parameters en route to more detailed physical characterization of a given asteroid. A future encounter of Gaspra by Galileo will be required to verify the present model.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 97; 1, Ma; 124-129
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  • 25
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    Scintillations of the Uranian kilometric radiation - Implications for the downstream magnetopause (1992)
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    Publication Date: 2011-08-24
    Description: Results are presented of the planetary radio astronomy observations conducted on board Voyager 2, with emphasis placed on the characteristics of the strong (3 to 6 dB) modulations of the broadband smooth Uranian radio emissions recorded from January 27-30, 1986, when the spacecraft was outbound from Uranus. The modulations were characterized by two superposed periods of about 100 sec and about 10 sec. It is suggested that the long-period modulation is due to the magnetopause surface waves, while the short-period modulations are due to the signature of ion cyclotron turbulence above the proton gyrofrequency, related to the magnetopause boundary layer.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; A6, J
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  • 26
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    A compositional classification scheme for meteoritic chondrules (1992)
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    Publication Date: 2011-08-24
    Description: A compositionally based classification scheme for chondrules is proposed that will help in systematizing the wealth of data available and disentangling the effects of nebular and subsequent processes. The classification is not by texture or the composition of a single phase, or a mixture of these two, but rather is a comprehensive, systematic approach which uses the composition of the two main chondrule components. This scheme is applicable to over 95 percent of the chondrules and is easily applied using an electron microprobe. It stresses the original diversity of the chondrules and the complex yet facile way in which they respond to parent-body metamorphism. Results using this classification scheme suggest that arguments against an important role of chondrules in determining the compositional trends of the chondrites have been premature.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 357; 6375,
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  • 27
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    Ulysses observations of escaping VLF emissions from Jupiter (1992)
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    Publication Date: 2011-08-24
    Description: The Ulysses URAP experiment has detected Jovian radio emissions in the VLF range at distances from Jupiter in excess of 1.5 AU. The URAP observations represent the first synoptic observations of Jupiter in the VLF band, from 3 to 30 kHz. In this band lie the low-frequency extent of the bKOM emission, the escaping continuum emission, and the Jovian type IIIs. Initial results indicate that the continuum varies in frequency with the solar wind ram pressure at Jupiter, whereas, the Jovian type IIIs appear to be controlled to some extent by the planetary rotation, often appearing when system III longitude 100 deg faces the spacecraft.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 19; 649-652
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  • 28
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    On the detectability of Jovian oscillations with infrared heterodyne measurements (1992)
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    Publication Date: 2011-08-24
    Description: A method is proposed for detecting Jovian global oscillations using IR heterodyne measurements in the lower stratosphere of the planet. Measurements of the S(0) and S(1) lines over a period of a few nights permitted the detection of modes with periods of 5 to 20 min and of Doppler shifts corresponding to velocities as low as 1 m/sec (which is less than the value reported by Schmider and Mosser, 1990 from observations of the Jovian troposphere in the visible range. Possible limitations of the method are pointed out.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 96; 15-26
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    Analysis of Voyager 2 images of Jovian lightning (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Magalhaes and Borucki (1991) reported that Voyager-2 images of Jupiter contained bright spots due to lightning activity that was confined to two narrow altitude bands centered at 49 deg N and 13.5 deg N latitude and to a single region near 60 deg N latitude. This paper describes the Voyager 2 imaging observations in detail and associates the positions of the lightning features in the images with particular cloud features. The energetics of the lightning storms on Jupiter is examined. It is found that the ratio of the energy dissipated by Jovian lightning to the thermal flux available to drive convection motions is about 3 decades larger than the terrestrial ratio.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 96; 1-14
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  • 30
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    Fall days of the SNC meteorites - Evidence for an SNC meteoroid stream, and a common site of origin (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Four of the SNC meteorites of putative Martian origin are falls. Two of these fell on October 3: Chassigny in 1815 and Zagami in 1962. The probability of this coincidence arising from random fall days is approximately 1 in 60. If this coincidence is not the result of chance, it suggests that some of the SNC meteorites are derived from a meteoroid stream. In that Chassigny and Zagami span nearly the full range of SNC lithologies and histories, the coincidence of fall days is consistent with suggestions that all of the SNCs came from a single site (impact crater) on their parent planet.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Meteoritics (ISSN 0026-1114); 27; 93-95
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  • 31
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    Impact-generated atmospheres over Titan, Ganymede, and Callisto (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The current distribution of atmospheres among Ganymede, Titan, and Callisto are presently accounted for by a process of competition between impact erosion and impact-furnished supply of atmosphile-laden late veneers. Titan's lower impact velocities have allowed it to accommodate an atmosphere, while Callisto and Ganymede remain barren. The model applied entails that the threshold impact velocity for atmospheric cratering by icy impactors be in the 10-14 km/sec range, consistent with the implications of the Schmidt and Housen (1987) crater-energy scaling for nonporous targets.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 95; 1-23
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  • 32
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    Ulysses radio and plasma wave observations in the Jupiter environment (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Unified Radio and Plasma Wave (URAP) experiment has produced new observations of the Jupiter environment, owing to the unique capabilities of the instrument and the traversal of high Jovian latitudes. Broad-band continuum radio emission from Jupiter and in situ plasma waves have proved valuable in delineating the magnetospheric boundaries. Simultaneous measurements of electric and magnetic wave fields have yielded new evidence of whistler-mode radiation within the magnetosphere. Observations of auroral-like hiss provided evidence of a Jovian cusp. The source direction and polarization capabilities of URAP have demonstrated that the outer region of the Io plasma torus supported at least five separate radio sources that reoccurred during successive rotations with a measurable corotation lag. Thermal noise measurements of the Io torus densities yielded values in the densest portion that are similar to models suggested on the basis of Voyager observations of 13 years ago. The URAP measurements also suggest complex beaming and polarization characteristics of Jovian radio components. In addition, a new class of kilometer-wavelength striated Jovian bursts has been observed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 257; 5076,; 1524-153
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  • 33
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    Ulysses dust measurements near Jupiter (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Submicrometer- to micrometer-sized particles were recorded by the Ulysses dust detector within 40 days of the Jupiter flyby. Nine impacts were recorded within 50 Jupiter radii with most of them recorded after closest approach. Three of these impacts are consistent with particles on prograde orbits around Jupiter and the rest are believed to have resulted from gravitationally focused interplanetary dust. From the ratio of the impact rate before the Jupiter flyby to the impact rate after the Jupiter flyby it is concluded that interplanetary dust particles at the distance of Jupiter move on mostly retrograde orbits. On 10 March 1992, Ulysses passed through an intense dust stream. The dust detector recorded 126 impacts within 26 hours. The stream particles were moving on highly inclined and apparently hyperbolic orbits with perihelion distances of greater than 5 astronomical units. Interplanetary dust is lost rather quickly from the solar system through collisions and other mechanisms and must be almost continuously replenished to maintain observed abundances. Dust flux measurements, therefore, give evidence of the recent rates of production from sources such as comets, asteroids, and moons, as well as the possible presence of interstellar grains.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 257; 5076,; 1550-155
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  • 34
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    On the inclusion of the hydrogen dimer in the analysis of Voyager IRIS spectra (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Empirical formulas are fitted to existing theoretical absorption spectra of H2-H2 pairs in the far-infrared allowing the inclusion of dimer absorption, parameterized with the height dependence of the para-hydrogen profile, in the calculations. Comparison between synthetic and Voyager IRIS spectra shows that once the dimer absorption is included it is now possible to reproduce the hydrogen portion of the IRIS spectrum to within the precision of the measurements.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 394; 1, Ju; L29-L32
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  • 35
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    In ecliptic observations of Jovian radio emissions by Ulysses - Comparison with Voyager results (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: During the Ulysses inbound cruise to Jupiter the Unified Radio and Plasma Wave (URAP) experiment observed a variety of the planet's radio components in the frequency range below 1 MHz. Most of these emissions were already detected by the Voyager Radio Astronomy and Plasma Wave experiments, however, with much less sensitivity and different spectral coverage. These different radio components within the URAP dynamic spectra are identified, and their appearance with the previous Voyager observations are compared.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 19; 12, J; 1307-131
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  • 36
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    Mechanism of Muong Nong-type tektite formation and speculation on the source of Australasian tektites (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The source crater of the youngest and largest of the tektite strewnfields, the Australasian strewnfield, has not been located. A number of lines of evidence indicate that the Muong Nong-type tektites, primarily found in Indochina, are more primitive than the much more abundant and widespread splash-form tektites, and are proximal to the source. In this study the spatial distribution of Muong Nong-type tektite sites and chemical character have been used to indicate the approximate location of the source. The variation of Muong Nong-type tektite chemical composition appears to be caused by mixing of two silicate rock end-members and a small amount of limestone, and not by vapor fractionation. The variation in composition is not random, and does not support in situ melting or multiple impact theories. The distribution of both Muong Nong and splash-form tektite sites suggest the source is in a limited area near the southern part of the Thailand-Laos border.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Meteoritics (ISSN 0026-1114); 27; 2, Ju
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  • 37
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    Neptune's polar cusp region - Observations and magnetic field analysis (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: This paper confirms and extends the results of Szabo et al. (1991) (which demonstrated some similarities of the Neptune's polar cusp region to the earth's cusp), but uses a different approach requiring plasma and vector magnetic field quantities. In addition, various MHD properties of the cusp-magnetopause boundary, which separates the cusp from the magnetosheath allowing thermal anisotropy, are obtained, including the magnetopause (MP) normal, mass, and normal momentum flux, the boundary speed (and thickness), and their relationships. Results demonstrate that the MP velocity is composed of two components: a propagation speed and the other component consistent with the rotational motion of the magnetosphere.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; A6, J
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  • 38
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    Titan's greenhouse and antigreenhouse effects (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Thermal mechanisms active in Titan's atmosphere are discussed in a brief review of data obtained during the Voyager I flyby in 1980. Particular attention is given to the greenhouse effect (GHE) produced by atmospheric H2, N2, and CH4; this GHE is stronger than that on earth, with CH4 and H2 playing roles similar to those of H2O and CO2 on earth. Also active on Titan is an antigreenhouse effect, in which dark-brown and orange organic aerosols block incoming solar light while allowing IR radiation from the Titan surface to escape. The combination of GHE and anti-GHE leads to a surface temperature about 12 C higher than it would be if Titan had no atmosphere.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Planetary Report (ISSN 0736-3680); 12; 3, Ma
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  • 39
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    The masses of Uranus and its major satellites from Voyager tracking data and earth-based Uranian satellite data (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Improved values for the masses of the Uranian system and the satellites Ariel, Umbriel, Titania, Oberon, and Miranda are obtained on the basis of an analysis of the Doppler-tracking data and star-satellite imaging from the Voyager 2 spacecraft combined with earth-based astrometric satellite observations. Masses are expressed as the product, the universal gravitational constant times the mass of the body, in units of (cu km/sq s). The satellite masses are (4.4 +/- 0.5) for Miranda, (90.3 +/- 8.0) for Ariel, (78.2 +/- 9.0) for Umbriel, (235.3 +/- 6.0) for Titania, and (201.1 +/- 5.0) for Oberon. Quoted errors are standard errors and are the present assessment of the true rather than the formal errors. The Uranus rotational pole orientation angles and gravity harmonic coefficients were fixed at the values determined by French et al. (1988) from stellar occultations of the Uranian rings observed from both the earth and Voyager 2 and from the occultation of the spacecraft radio signal.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astronomical Journal (ISSN 0004-6256); 103; 6, Ju
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  • 40
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    Asteroid families - An initial search (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A stereo examination was conducted for clusters in three-dimensional proper element space within a sample of both numbered and faint Palomar-Leiden Survey (PLS) asteroids. The clusters were then objectively filtered for small Poisson probability of chance occurrence; 104 were accepted as families with 4- to 12-member populations, and are interpreted as impact-generated. Structure is common in the well-populated families: the better-sampled families are accordingly discussed in terms of their geometry and taxonomy. Some families are very rich in faint PLS members.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 96; 2, Ap
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  • 41
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    Mars secular obliquity change due to the seasonal polar caps (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: There is a weak positive feedback mechanism between the astronomy and meteorology of Mars. The mechanism is this: the seasonal waxing and waning polar caps cause small changes in Mars' dynamical flattening. Because the changes in flattening are out of phase with the sun, there is a net annual solar torque on the planet which increases the angle between the equatorial and orbital phanes. On the basis of Viking observations of the present climate and simple atmospheric models of past climates, these seasonal shifts of mass between the atmosphere and polar caps are capable of secularly increasing Mars' obliquity by about 1 or 2 deg since the origin of the solar system. Thus, the climate, driven largely by the axial tilt, reacts back on the planet and slightly enhances the seasons on Mars as time progresses. More sophisticated models will probably not change this result much; therefore this mechanism probably produced only minor changes in Mars' climate. It causes negligible changes in the axial tilt and climate of the earth.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; E2, F
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  • 42
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    Lunar impact basins and crustal heterogeneity - New western limb and far side data from Galileo (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Multispectral images of the lunar western limb and far side obtained from Galileo reveal the compositional nature of several prominent lunar features and provide new information on lunar evolution. The data reveal that the ejecta from the Orientale impact basin (900 kilometers in diameter) lying outside the Cordillera Mountains was excavated from the crust, not the mantle, and covers pre-Orientale terrain that consisted of both highland materials and relatively large expanses of ancient mare basalts. The inside of the far side South Pole-Aitken basin (greater than 2000 kilometers in diameter) has low albedo, red color, and a relatively high abundance of iron- and magnesium-rich materials. These features suggest that the impact may have penetrated into the deep crust or lunar mantle or that the basin contains ancient mare basalts that were later covered by highlands ejecta.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 255; 570-576
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    The age of the meteorite recovery surfaces of Roosevelt County, New Mexico, USA (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We have obtained minimum age estimates for the sand units underlying the two largest meteorite deflation surfaces in Roosevelt County, New Mexico, USA, using thermoluminescence dating techniques. The dates obtained ranged from 53.5 (+/- 5.4) to 95.2 (+/- 9.5) ka, and must be considered lower limits for the terrestrial ages of the meteorites found within these specific deflation surfaces. These ages greatly exceed previous measurements from adjacent meteorite-producing deflation basins. We find that Roosevelt County meteorites are probably terrestrial contemporaries of the meteorites found at most accumulation zones in Antarctica. The apparent high meteorite accumulation rate reported for Roosevelt County by Zolensky et al. (1990) is incorrect, as it used an age of 16 ka for all Roosevelt County recovery surfaces. We conclude that the extreme variability of terrestrial ages of the Roosevelt County deflation surfaces effectively precludes their use for calculations of the meteorite accumulation rate at the Earth's surface.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Meteoritics (ISSN 0026-1114); 27; 4; p. 460-462.
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  • 44
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    Magnetic field observations during the Ulysses flyby of Jupiter (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Ulysses magnetic field measurements confirmed the general structure of the dayside magnetosphere and showed that the importance of the current sheet dynamics extends well into the middle and outer magnetosphere. On the dusk side, the magnetic field was found to be swept back significantly toward the magnetotail. It is pointed out that the external current densities need to be modified with respect to previous observations on the inbound pass which shows that Jovian magnetic and magnetospheric models are highly sensitive to both the intensity and the structure assumed for the current sheet. Data obtained revealed that all boundaries and boundary layers in the magnetosphere have a very complex microstructure.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 257; 5076,
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  • 45
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    A physical model of Titan's aerosols (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A modeling effort is presented for the nature of the stratospheric haze on Titan, under several simplifying assumptions; chief among these is that the aerosols in question are of a single composition, and involatile. It is further assumed that a one-dimensional model is capable of simulating the general characteristics of the aerosol. It is suggested in this light that the detached haze on Titan may be a manifestation of organized, Hadley-type motions above 300 km altitude, with vertical velocities of 1 cm/sec. The hemispherical asymmetry of the visible albedo may be due to organized vertical motions within the upper 150-200 km of the haze.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 95; 24-53
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  • 46
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    Phenomenology of Neptune's radio emissions observed by the Voyager planetary radio astronomy experiment (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Neptune flyby in 1989 added a new planet to the known number of magnetized planets generating nonthermal radio emissions. We review the Neptunian radio emission morphology as observed by the planetary radio astronomy experiment on board Voyager 2 during a few weeks before and after closest approach. We present the characteristics of the two observed recurrent main components of the Neptunian kilometric radiation, i.e., the 'smooth' and the 'bursty' emissions, and we describe the many specific features of the radio spectrum during closest approach.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; A12; p. 19,201-19,211.
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  • 47
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    Orographically forced oscillations in a dynamical model of the Martian atmosphere (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The barotropic, orographically-forced intraseasonal oscillations of the Martian atmosphere are presently analyzed by means of a single-layer shallow-water model. An oscillation with 85-Martian day mean period is noted in a time-series of the model global atmospheric angular momentum, and its robustness is verified. The oscillation has a standing zonal component whose centers of action are located upstream and downstream of salient orographic features. A resemblance arises between the oscillation's northern-hemisphere features and those of the terrestrial 40-day oscillation.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 100; 2; p. 598-607.
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  • 48
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    Thermal spectroscopy of Neptune - The stratospheric temperature, hydrocarbon abundances, and isotopic ratios (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: NASA-IRTF observations of Neptune's disk-averaged spectrum are presently used, in conjunction with a lower-resolution spectrum, to furnish a more reliable absolute intensity calibration of portions of Neptune's disk-averaged spectrum. The temperature profile adopted is consistent with the size and shape of the H2 J = 3-1 quadrupole feature detected in the emission. High-resolution measurements of (C-13C-12)H6 and (C-12)2H6 imply C-12/C-13 of 78 +/- 26; this is consistent with solar and telluric values.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 100; 2; p. 541-555.
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  • 49
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    Jovian large-scale stratospheric circulation (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: An attempt is made to diagnose the annual-average mean meridional residual Jovian large-scale stratospheric circulation from observations of the temperature and reflected sunlight that reveal the morphology of the aerosol heating. The annual mean solar heating, total radiative flux divergence, mass stream function, and Eliassen-Palm flux divergence are shown. The stratospheric radiative flux divergence is dominated the high latitudes by aerosol absorption. Between the 270 and 100 mbar pressure levels, where there is no aerosol heating in the model, the structure of the circulation at low- to midlatitudes is governed by the meridional variation of infrared cooling in association with the variation of zonal mean temperatures observed by IRIS. The principal features of the vertical velocity profile found by Gierasch et al. (1986) are recovered in the present calculation.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 100; 1; p. 245-259.
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  • 50
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    Impacts and tectonism in Earth and moon history of the past 3800 million years (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The moon's surface, unlike the Earth's, displays a comparatively clear record of its past bombardment history for the last 3800 Myr, the time since active lunar tectonism under the massive premare bombardment ended. From Baldwin's (1987) tabulation of estimated ages for a representative sample of large lunar craters younger than 3800 Ma, six major cratering episodes can be discerned. These six bombardment episodes, which must have affected the Earth too, appear to match in time the six major episodes of orogenic tectonism on Earth, despite typical resolution errors of +/- 100 Myr and the great uncertainties of the two chronologies. Since more highly resolved events during the Cenozoic and Mesozoic Eras suggest the same correlation, it is possible that large impacts have influenced plate tectonics and other aspects of geologic history, perhaps by triggering flood basalt eruptions.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Earth, Moon, and Planets (ISSN 0167-9295); 58; 2; p. 145-152.
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  • 51
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    A prediction of Mars seismicity from surface faulting (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The shallow seismicity of Mars has been estimated by measurement of the total slip on faults visible on the surface of the planet throughout geologic time. Seismicity was calibrated with estimates based on surface structures on the moon and measured lunar seismicity that includes the entire seismogenic lithosphere. Results indicate that Mars is seismically active today, with a sufficient number of detectable marsquakes to allow seismic investigations of its interior.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 258; 5084; p. 979-981.
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  • 52
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    DSN observations of Titan (1992)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: When using DSS 14 in a monostatic configuration, radar observations of Titan show that Titan is a diffuse reflector with a relative radar cross section of 0.14+/-0.03. No hot spots were observed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: The Telecommunications and Data Acquisition Report; p 377-379
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  • 53
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    Cassini/Huygens: A mission to Saturn and Titan (1992)
    In:  CASI
    Details
    Publication Date: 2008-05-11
    Description: The Cassini/Huygens mission is designed to explore the Saturnian system. The Cassini spacecraft comprises a NASA provided Saturn orbiter and an ESA supplied Titan atmospheric probe named Huygens. The scientific objectives of the mission are described and the main characteristics of the payload are provided. Since emphasis is on ESA's contribution to the mission, a detailed description of the Huygens probe mission phase is given and the major features of the probe design are discussed. An overview of the probe operations center is provided.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Environment Observation and Climate Modelling Through International Space Projects. Space Sciences with Particular Emphasis on High-Energy Astrophysics; p 189-194
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  • 54
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    Ulysses radio occultation observations of the Io plasma torus during the Jupiter encounter (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Radio signals from Ulysses were used to probe the Io plasma torus (IPT) shortly after the spacecraft's closest approach to Jupiter. The frequencies of the two downlinks at S-band (2.3 gigahertz) and X-band (8.4 gigahertz) were recorded, differenced, and integrated in order to derive the columnar electron density of the IPT. The measurements agree qualitatively with contemporary models of the IPT based on Voyager data, but significant differences are apparent as well. The overall level of the IPT electron density is approximately the same as the prediction, implying that the amount of gas (or plasma) injected from Io is similar to that observed during the Voyager era. On the other hand, the IPT seems to be less extended out of the centrifugal equator, implying a smaller plasma temperature than predicted.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 257; 5076,; 1531-153
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  • 55
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    A reconsideration of the effects of terminator ionopause height on the nightward ion transport at Venus (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The ionopause altitude near the terminator is a crucial parameter for studies dealing with the maintenance of the nightside ionosphere of Venus. It is generally thought that, during high solar wind dynamic pressures (P(SW)) or during solar minimum conditions, the ionopause comes down to very low altitudes so that the dayside ionosphere is not able to supply sufficient plasma to maintain the observed nightside densities. However, there are a number of workable definitions of the ionopause. Near the terminator, the altitude of the ionopause differs considerably depending upon the definition. The ionopause deduced from the radio occultation experiment as well as the pressure ionopause can be significantly lower than the density ionopause deduced from the Langmuir probe at these locations. The latter refers to the altitude where the electron density falls to 100/cu cm. Using in situ data from the Pioneer Venus Orbiter, it is shown that the density ionopause remains fairly high even for high P(SW) conditions. Simple quantitative estimates indicate that significant flow of plasma is still possible under these conditions. Thus, nightward transport of plasma during high P(SW) conditions may be more efficient than has been assumed so far. Since such conditions are more prevalent during solar cycle minimum, it is argued that transport may be relevant in the maintenance of nightside ionosphere at that time also.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; A9, S; 13
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    The -SiH vibrational stretch as an indicator of the oxidation state of silicon in a cometary or asteroidal regolith (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: It has been experimentally shown that the position of the -SiH fundamental vibrational stretch is very sensitive to the chemical environment surrounding the Si atom. Si in an oxidizing environment will display an -SiH feature near 4.4 microns, whereas Si in a reducing grain could be responsible for a feature at 4.74 microns. It is further shown that, as an oxidized grain is reduced, the -SiH fundamental shifts to longer wavelengths through a series of intermediate bands.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 98; 2, Au; 207-210
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    Images and topographic relief at the north pole of Venus (1992)
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    Publication Date: 2011-08-24
    Description: The analysis of unique coverage of the north pole of Venus using a subset of 13 images from a total of about 775 synthetic aperture radar orbits during cycle 1 of the Magellan mission is reported. Images at 13 distinctly different azimuths are reported that range over 360 deg in longitude and that show the topographic relief at vastly different imaging geometries at intervals of about 20 deg. A pair of intersecting or crossing orbits is used to assess the topographic relief with stereo radargrammetric techniques, and to refine this assessment using a multiimage clinometric approach. It is shown that the pole is located in accentuated topography with elevation differences in the range of no more than 1 km. It is concluded that pinpointing the location of the pole from the overlapping images and standard mission data is accurate to within about 100 pixels or 8 km (RMS).
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; E8, A; 13
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    Magellan observations of Alpha Regio - Implications for formation of complex ridged terrains on Venus (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The deformational features that make up the complex ridged terrain (CRT) of Alpha Regio are characterized, and observations of these features and their interpretations are used to evaluate quantitative models for the formation of Alpha Regio. In particular, two models are considered: a hotspot or mantle plume model and a coldspot or mantle downwelling model. Based on an analysis of the observed morphology of structures, their distribution, superposition and crosscutting relationships, and Magellan altimetry, a sequence of deformational events is suggested, and the observed topography, tectonics, and volcanism are compared with the predictions of the hotspot and coldspot models. It is found that a number of observations are more consistent with the downwelling than a hotspot model. This is particularly true of margin-parallel compressional features near the plains-CRT boundary in much of Alpha Regio.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; E8, A; 13
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    Features on Venus generated by plate boundary processes (1992)
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    Publication Date: 2011-08-24
    Description: Various observations suggest that there are processes on Venus that produce features similar to those associated with plate boundaries on earth. Synthetic aperture radar images of Venus, taken with a radar whose wavelength is 12.6 cm, are compared with GLORIA images of active plate boundaries, obtained with a sound source whose wavelength is 23 cm. Features similar to transform faults and to abyssal hills on slow and fast spreading ridges can be recognized within the Artemis region of Venus but are not clearly visible elsewhere. The composition of the basalts measured by the Venera 13 and 14 and the Vega 2 spacecraft corresponds to that expected from adiabatic decompression, like that which occurs beneath spreading ridges on earth. Structures that resemble trenches are widespread on Venus and show the same curvature and asymmetry as they do on earth. These observations suggest that the same simple geophysical models that have been so successfully used to understand the tectonics of earth can also be applied to Venus.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; E8, A; 13
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    An unusual volcano on Venus (1992)
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    Publication Date: 2011-08-24
    Description: Materials that issued from an unusual Venusian volcano produced (1) a complex domical structure about 100 km across with thick, broad flow lobes up to 41 wide, (2) an extensive sheet of thick flows, and (3) radar-bright surfaces that extend to 360-400 km from the volcano. Altimetry indicates that the relief of the domical structure is about 0.5-1.1 km. The lobes and flows have prominant regularly spaced ridges about 686-820 m apart. Thick flows with large ridge separations and broad lobes are rare on Venus. The viscosities of these flows were larger than those of most lava flows on Venus. Comparisons of the dimensions of the volcano's lobes with lava flows on earth suggest that the Venusian lavas may have large silica contents. Radar-bright surfaces around the volcano may represent the result of an explosive eruption or very thin deposits of low-viscosity lavas. Thus, the radar-bright surfaces and lavas of the volcano were derived from a magma that differentiated within the crust or mantle of Venus. The differentiation produced (1) a gas-rich low-viscosity phase, (2) high-viscosity lavas, and (3) a residual primary magma.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; E8, A; 13
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    Reflection and emission properties on Venus - Alpha Regio (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Procedures developed from Hagfors' (1964) scattering model have been used with success to extract various properties (reflectivity, emissivity, slope, etc.) from both Pioneer Venus and Magellan data. However, under certain circumstances, such as physically rough areas or areas of nonhomogeneous composition, Hagfors' model may lead to serious errors in the interpretation of radar and radiometry data. The Magellan-derived surface properties are examined for some areas of below average emissivity in Alpha Regio and in an area to the east of Alpha, Crater Stuart, in order to determine if Hagfors' model is applicable. Methods of classical multiple scattering theory are also applied to show that enhanced radar backscattering and depressed thermal emission can be expected with a matrix of silicic or mafic rocks embedded in low loss soils.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; E8, A; 13
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    Dynamic crystallization experiments on the Angra dos Reis achondritic meteorite (1992)
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    Publication Date: 2011-08-24
    Description: The types of cooling histories necessary to produce the porphyritic texture and the observed mineral assemblage in Angra dos Reis (ADOR) achondritic meteorite, which, on the basis of its trace element characteristics was considered to be a cumulate with a recrystallized texture, while a recent model suggested that ADOR is a porphyry. Dynamic crystallization experiments were conducted with nucleation conditions varied by melting the starting material at different degrees of superheat. The results show that, at low pressure, a volcanic or hypabyssal history of ADOR is possible. The most likely history involved cooling from a slightly subliquidus temperature with a relatively high and irregular nucleation density resulting in a granular texture with the poikilitic fassaite growing late; accumulation of some crystal is tought to be probable.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Earth and Planetary Science Letters (ISSN 0012-821X); 111; 2-4,
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  • 63
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    Venus thermospheric response to short-term solar variations (1992)
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    Publication Date: 2011-08-24
    Description: The mechanism responsible for cooling the dayside thermosphere of Venus from about 700 K to 300 K (Noll and McElroy, 1972) is examined by analyzing in situ measurements made by the Pioneer Venus Orbiter of the weak response of the thermosphere to short-term solar variations related to 27-day solar rotation. It is shown that, in order to cool the Venus dayside thermosphere to observed levels and to simultaneously explain the weak 27-day variations in the atmosphere, it is necessary to invoke strong CO2 cooling which is controlled principally by collisions of CO2 with atomic oxygen.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Advances in Space Research (ISSN 0273-1177); 12; 9, Se
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    Imaging of Venus from Galileo - Early results and camera performance (1992)
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    Publication Date: 2011-08-24
    Description: Three images of Venus have been returned so far by the Galileo spacecraft following an encounter with the planet on UT February 10, 1990. The images, taken at effective wavelengths of 4200 and 9900 A, characterize the global motions and distribution of haze near the Venus cloud tops and, at the latter wavelength, deep within the main cloud. Previously undetected markings are clearly seen in the near-infrared image. The global distribution of these features, which have maximum contrasts of 3 percent, is different from that recorded at short wavelengths. In particular, the 'polar collar', which is omnipresent in short wavelength images, is absent at 9900 A. The maximum contrast in the features at 4200 A is about 20 percent. The optical performance of the camera is described and is judged to be nominal.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Advances in Space Research (ISSN 0273-1177); 12; 9, Se; 91-103
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    Radio observations of the Jovian magnetic field (1992)
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    Publication Date: 2011-08-24
    Description: Radio observations of Jupiter are reviewed and discussed in relation to the planet's magnetic field. Early ground-based decameter- and decimeter-wave observations lead to a first estimate of the magnetic field strength which was subsequently confirmed by space-borne measurements. Decametric, hectometric and decimetric measurements of the Jovian rotation period offer the possibility of detecting a real change in the magnetic field structure within the next few decades. Solar wind control of the radio emission allows inferences to be made concerning the magnetic field and the emission regions at decametric, hectometric and kilometric frequencies. The decametric and the hectometric radiation may originate in hollow-cone emission sources at high (auroral) latitudes on Jupiter. The broad-band kilometric emission appears to originate at the outer edge of the Io torus.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Advances in Space Research (ISSN 0273-1177); 12; 8, Au; 155-164
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    The magnetic field of Neptune (1992)
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    Publication Date: 2011-08-24
    Description: A model is given of the planetary magnetic field of Neptune based on a spherical harmonic analysis of the observations obtained by the Voyager 2. Generalized inverse techniques are used to partially solve a severely underdetermined inverse problem, and the resulting model is nonunique since the observations are limited in spatial distribution. Dipole, quadrupole, and octupole coefficients are estimated independently of other terms, and the parameters are shown to be well constrained by the measurement data. The large-scale features of the magnetic field including dipole tilt, offset, and harmonic content are found to characterize a magnetic field that is similar to that of Uranus. The traits of Neptune's magnetic field are theorized to relate to the 'ice' interior of the planet, and the dynamo-field generation reflects this poorly conducting planet.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Advances in Space Research (ISSN 0273-1177); 12; 8, Au
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    Magnetic boundaries of the outer planets - A review (1992)
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    Publication Date: 2011-08-24
    Description: The static and dynamic characteristics of the magnetopauses of the outer planets, as well as their estimated large scale shapes, are reviewed and compared to each other and to those of the earth. Various unique features will be stressed. For example, because of the severe asymmetric nature of the main magnetic fields of Uranus and Neptune (due to significantly displaced and tilted magnetic dipole sources), their magnetospheres are (rapidly) rotating obstacles to solar wind flow, and their magnetopauses respond to that large, rapid variation. Waves or wavelike features on Uranus' boundary, and evidence for boundary layer plasmas at all of the outer planets, is reviewed. Unexpectedly, Voyager 2 encountered a magnetospheric cusp as it entered Neptune's magnetosphere. Observations of that region will be discussed, especially with regard to its structure and the apparent boundary layer plasmas around that complex boundary. Waves on the magnetopause of Saturn with periods of 5 to 30 min have been observed (as at earth). Comparisons of the estimated thicknesses of the observed magnetopauses will be made, including that of earth.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Advances in Space Research (ISSN 0273-1177); 12; 8, Au
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    Neptune's non-thermal radio emissions - Phenomenology and source locations (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: During the inbound and the outbound leg of Voyager 2's encounter with Neptune, the Planetary Radio Astronomy (PRA) experiment aboard the spacecraft detected short radio bursts at frequencies within the range of about 500-1300 kHz, and broad-banded smoothly varying emission patterns within the frequency range from about 40-800 kHz. Both emissions can be described in terms of a period of 16.1 hours determining Neptune's rotation period. Furthermore, just near closest approach, a narrow-banded smoothly varying radio component was observed occurring between 600 and 800 kHz. After giving a brief overview about some general characteristics of Neptune's nonthermal radio emission, the source locations of Neptune's emission components are determined, using an offset tilted dipole model for Neptune's magnetic field. Assuming that the emission originates near the electron gyrofrequency a geometrical beaming model is developed in order to fit the observed emission episodes.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Kleinheubacher Berichte (ISSN 0343-5725); 35; 821-830
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    The Spaceguard Survey - Protecting the earth from cosmic impacts (1992)
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    Publication Date: 2011-08-24
    Description: The conclusions of the NASA International Near-Earth-Object Detection Workshop (May 1991-January 1992) are summarized. Near-earth asteroids and short-period comets constitute about 90 percent of potential earth-impacting projectiles. The greatest risk is from those with diameters greater than 1 km. The objective of a near-earth object survey is to find such objects, calculate their long-term orbital trajectories, and identify any that may impact the earth over the next several centuries. There will generally be a period of at least several decades to take corrective action if any potential earth-impactors are found. A region of space extending outward from the earth to approximately the inner edge of the main asteroid belt must be monitored. Detection can be by reflected sunlight or infrared. Though faint, the objects should be readily detectable with ground-based telescopes, and thus there is no need for a more expensive space-based system.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Mercury (ISSN 0047-6773); 21; 3, Ma; 103-106
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    Comparison of density waves in the rings of Saturn and Uranus (1992)
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    Publication Date: 2011-08-24
    Description: The similarity of density waves in the rings of Saturn and Uranus are addressed. It is found that all ring systems are grossly similar in that they all encircle the primary in its equatorial plane and exhibit responses to resonant satellite perturbations. The dominant response of Saturn's rings is the clearing of gaps and generation of density and bending waves. The Uranian rings appear to be confined by the presence of shepherd satellites. Three possible density waves have been identified, two in the epsilon ring and one in the delta ring.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Advances in Space Research (ISSN 0273-1177); 12; 11, N
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    Chemistry of the surface and lower atmosphere of Venus (1992)
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    Publication Date: 2011-08-24
    Description: A comprehensive overview of the chemical interactions between the atmosphere and surface of Venus is presented. Earth-based, earth-orbital, and spacecraft data on the composition of the atmosphere and surface of Venus are presented and applied to quantitative evaluations of the chemical interactions between carbon, hydrogen, sulfur, chlorine, fluorine, and nitrogen-containing gases and possible minerals on the Venus surface. The calculation results are used to predict stable minerals and mineral assemblages on the Venus surface to determine which, if any, atmospheric gases are buffered by mineral assemblages on the surface, and to critically review and assess prior work on atmosphere-surface chemistry on Venus. It is concluded that the CO2 pressure on Venus is comparable to the CO2 equilibrium partial pressure developed by the calcite + wollastonite + quartz assemblage at the mean Venus surface temperature of 740 K.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astronomicheskii Vestnik (ISSN 0320-930X); 26; 2, Ma; 3-65
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    Millimeter-wave observations of Saturn, Uranus, and Neptune - CO and HCN on Neptune (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Saturn, Uranus, and Neptune were observed at millimeter wavelengths with the IRAM 30 m telescope. The major result is the detection of CO and HCN in Neptune's stratosphere, with respective mixing ratios of (6.5 +/- 3.5) x 10 exp -7 and (3 +/- 1.5) x 10 exp -10. CO seems to be present in Neptune's troposphere as well and to slowly decrease with altitude (scale height about 200 km). HCN is probably formed from reactions between CH3 and N, which can be supplied in sufficient amounts by escape from Triton's atmosphere. The origin of CO, however, is more problematic, because: (1) thermochemical models fail to reproduce the observed abundance by a factor of about 1000; and (2) an external source would require a very large flux of oxygen. CO appears to be at least 15 times less abundant on Uranus than on Neptune. Finally, an upper limit of 10 exp -7 for CO in Saturn's stratosphere suggests an internal origin for Saturnian CO.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 392; 2, Ju
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  • 73
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    Comment on 'Evidence of Saturn's magnetic field anomaly from Saturnian kilometric radiation high-frequency limit' by P. Galopeau et al (1992)
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    Publication Date: 2011-08-24
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; A6, J
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    Venus - Satellite orbital decay, ephemeral ring formation, and subsequent crater production (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The question of whether most or even all of the observed impact features on the surface of Venus can be derived from satellitic material is addressed. Consideration is given to the hypothesis that the craters retained on the surface of Venus were all emplaced within a relatively short interval, as collisional fragments of a former satellite impacted the surface. It is concluded that the areal density of craters may provide no absolute age information at all: the craters may be as recent as the last significant satellite loss event.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 19; 10, M
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    Partition coefficients for iron between plagioclase and basalt as a function of oxygen fugacity - Implications for Archean and lunar anorthosites (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: As a prelude to determinations of the content of total iron as FeO(T) in melts in equilibrium with calcic anorthosites, the partition coefficients (Ds) for FeO(T) between calcic plagioclase and basaltic melt were determined, as a function of oxygen fugacity (f(O2)), for a basaltic composition that occurs as matrices for plagioclase megacrysts. Results showed that, at the liquidus conditions, the value of D for FeO(T) between calcic plagioclase and tholeiitic basalt changed little (from 0.030 to 0.044) between the very low f(O2) of the iron-wustite buffer and that of the quartz-fayalite-magnetite (QFM) buffer. At fugacities above QFM, the value for D increased rapidly to 0.14 at the magnetite-hematite buffer and to 0.33 in air. The increase in D results from the fact that, at f(O2) below QFM, nearly all of the Fe is in the Fe(2+) state; above QFM, the Fe(3+)/Fe(2+) ratio in the melt increases rapidly, causing more Fe to enter the plagioclase which accepts Fe(3+) more readily than Fe(2+).
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 56; 5, Ma
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    An interplanetary dust particle with links to CI chondrites (1992)
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    Publication Date: 2011-08-24
    Description: W7013F5 is a chondritic, hydrated interplanetary dust particle whose composition and mineralogy is nearly identical to that found in the CI chondrites. Transmission electron microscope observations show that the phyllosilicates in W7013F5 consist largely of a coherent undergrowth of Mg-Fe serpentine and Fe-bearing saponite on the unitcell scale. This distinctive intergrowth of phyllosilicates has only been observed previously in the CI chondrites. Other secondary minerals in W7013F5 include Mg-Fe carbonates, magnetite, and pentlandite. The mineral assemblage in W7013F5 is generally not as oxidized as that in the CI chondrites. The presence of kamacite in W7013F5 indicates that the particle is extraterrestrial, and a thin amorphous rim surrounding the particle provides evidence that it is not a piece of a meteorite that fragmented during transit through the atmosphere. The apparent lack of hydrated IDPs with CI mineralogy and chemistry may indicate that CI-type dust-producing asteroids are uncommon in the asteroid belt.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 56; 3, Ma
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    Isolation of major Venus thermospheric cooling mechanism and implications for earth and Mars (1992)
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    Publication Date: 2011-08-24
    Description: The additional cooling mechanism responsible for the unexpectedly cold dayside Venus thermosphere is isolated. Consideration is given not only to the condition that the calculated temperatures must be reduced to the observed dayside temperatures but also that the theoretical temperature variations must be in accord with the observed low amplitude of temperature variations associated with the 27-d variations of the sun. It is found that the low amplitude of the 27-d oscillations, combined with the cooling necessary for observed 300-K dayside temperatures, cannot be explained by eddy conduction cooling and can only be explained by very strong 15-micron cooling. Implications of the decrease in amplitude of the 11-yr Venus thermospheric variability due to the 15-micron thermostat effect are examined.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; A4, A
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    A theory for narrow-banded radio bursts at Uranus - MHD surface waves as an energy driver (1992)
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    Publication Date: 2011-08-24
    Description: A possible scenario for the generation of the narrow-banded radio bursts detected at Uranus by the Voyager 2 planetary radio astronomy experiment is described. In order to account for the emission burstiness which occurs on time scales of hundreds of milliseconds, it is proposed that ULF magnetic surface turbulence generated at the frontside magnetopause propagates down the open/closed field line boundary and mode-converts to kinetic Alfven waves (KAW) deep within the polar cusp. The oscillating KAW potentials then drive a transient electron stream that creates the bursty radio emission. To substantiate these ideas, Voyager 2 magnetometer measurements of enhanced ULF magnetic activity at the frontside magnetopause are shown. It is demonstrated analytically that such magnetic turbulence should mode-convert deep in the cusp at a radial distance of 3 RU.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; A4, A
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    The abundance and distribution of water vapor in the Jovian troposphere as inferred from Voyager IRIS observations (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Voyager IRIS spectra of the Jovian North Equatorial Belt (NEB) hot spots are reanalyzed using a radiative transfer model which includes the full effects of anisotropic multiple scattering by clouds. The atmospheric model includes the three thermochemically predicted cloud layers, NH3, NH4SH, and H2O. Spectrally dependent cloud extinction is modeled using Mie theory and the refractive indices of NH3 ice, NH4SH ice, water, and H2O ice. The upper tropospheric temperature profile, gas abundances, height-dependent parahydrogen profile, and vertical distribution of NH3 cloud opacity are retrieved from an analysis of the far-infrared (180-1200/cm) IRIS observations. With these properties constrained, the 5-micron (1800-2300/cm) observations are analyzed to determine the atmospheric and cloud structure of the deeper atmosphere (P of greater than 1.5 bars). The results show that the abundance of water is at least 1.5 times solar with 2 times solar (0.00276 mixing ratio relative to H2) providing the best-fit to the Voyager IRIS hot spot observations.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 388; 648-668
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    Triton - Voyager's finale (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The investigation of the Neptunian satellite Triton by the Voyager 2 is described with interpretations of the object's nature and composition. The orbit, seasonal cycle, and southern-hemisphere solstice are described, and the composition of the satellite is discussed. Triton's mass and radius are known, and the objects is made up of about 70 percent rock and organics and 30 percent ice by mass. Triton's interior is warm and geologically active considering its distance from the sun, and large amounts of frozen methane and nitrogen are theorized to contribute to the object's high reflectivity. Also noted in the Voyager color images are creeping ice, cryogenic lava, and dark streaks on the south polar cap from nitrogen gas leaks driven by a type of greenhouse effect. Triton represents a class of satellite that has not been observed previously: a moon-sized body in a retrograde inclined orbit from the class of objects that coalesced to form Neptune.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Planetary Report (ISSN 0736-3680); 12; 14-17
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    The atmosphere of Neptune - An analysis of radio occultation data acquired with Voyager 2 (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The vertical structure of Neptune's atmosphere is studied on the basis of recordings of the tracking signals received from Voyager 2 during its occultation by Neptune. The measurements began at a planetographic latitude of 62 deg north and ended near 45 deg south, and cover an altitude interval of about 5000 km. The 1-bar isobaric surface has equatorial and polar radii of 24,766 +/-15 km and 24,342 +/-30 km, respectively, and a corresponding oblateness of 0.0171 +/-0.0014. At this pressure, the temperature was 72 +/-2 K. The tropopause was detected approximately 40 km above the 1-bar level at a pressure of about 100 mbar. A comparison with IR observations indicates that the gas at the tropopause consists of 78-84-percent hydrogen by number density with the rest being mostly helium. The temperature in this region was 52 +/-2 K.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astronomical Journal (ISSN 0004-6256); 103; 967-982
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  • 82
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    Recent grazing impacts on the earth recorded in the Rio Cuarto crater field, Argentina (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: An anomalous alignment of oblong rimmed depressions has been observed on the otherwise featureless farmland of the Argentine Pampas. It is argued here, from sample analysis and by analogy with laboratory experiments, that the structure resulted from a low-angle impact and ricochet of a chondritic body originally 150-300 m in diameter.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 355; 234-237
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  • 83
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    A thermal model for the seasonal nitrogen cycle on Triton (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The seasonal N2-cycle model presently used to characterize such observed phenomena on Triton as atmospheric pressure and surface albedo features at the time of the Voyager encounter incorporates diurnal and seasonal subsurface heat conduction, and can account for the heat capacity of N2 frost deposits. The results obtained by this model differ from those of previous studies in that they do not predict the seasonal freezing-out of the Triton atmosphere; even for a wide range of input parameters, the bright southern polar cap is seen as rather unlikely to be N2. The results support the microphysical arguments for the presence of either dark or smooth translucent N2 frosts on the Triton surface.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 99; 2; p. 273-288.
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    Variable oxygen airglow on Venus as a probe of atmospheric dynamics (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: High-resolution images are presented of an oxygen airglow that arises during downwelling at an altitude of about 95 km on the nightside of Venus. Oxygen atoms are formed by photolysis of CO2 on the sunlit hemisphere and are then transported to the nightside, where they recombine during descent. The newly formed molecular oxygen emits radiation to produce the airglow. Localized, short-lived regions of emission and neighboring dark areas are observed, demonstrating the potential of such observations to constrain atmospheric dynamics at this little-studied and important altitude in the Venusian mesosphere.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 359; 6395; p. 516-519.
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  • 85
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    Geology of Venera 8 landing site region from Magellan data - Morphological and geochemical considerations (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Morphological and geochemical aspects of the geology of the Venera 8 landing site region are examined on the basis of two approaches: an analysis of Magellan data for the Venera/Vega sites where chemical composition of the surface material was determined, and continuation of the search for terrestrial igneous rocks which are the K2O-U-Th analogs of the Venera 8 material. Based on the first approach, it is determined that steep-sided volcanic domes are associated with the sites where a nontholeiitic composition of the surface material was determined. In the second approach, it is discovered that the chemical analogs of the Venera 8 material are not confined to more evolved igneous rocks but may also include a group of more mafic, rather primitive rocks. A common feature of the rocks in these two groups is chemical signatures of some involvement of the material of the earth's continental crust in their magma genesis.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; E10; p. 16,315-16,335.
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  • 86
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    Galileo's progress (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Data obtained to date by the Galileo spacecraft launched in October 1989 are discussed. It is noted that in April 1991 the spacecraft's high-gain antenna failed to deploy from its furled position. Since then, communications including return of images of the Gaspra asteroid have been performed through the low-gain antenna. It is considered to be possible to accomplish the majority of orbiter scientific objectives without the high-gain antenna including the return of high resolution images.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Spaceflight (ISSN 0038-6340); 34; 10; p. 327-331.
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  • 87
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    Small-scale fracture patterns on the volcanic plains of Venus (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Linear features with a regular spacing of about 1 km in the gridded plains of Guinevere Planitia observed in Magellan radar images of Venus are examined. Many sets of parallel, regularly spaced lineations similar to the closely spaced features of the gridded plains were found. These sets of parallel lineations, which are interpreted to be fractures, typically cover areas with dimensions of hundreds of kilometers. Several examples of these regular lineations are characterized in terms of their average fracture spacing, which is between 1 and 2.5 km; the scatter in individual spacings is about +/- 1/3 the average. It is hypothesized that these features are extension fractures in the brittle upper layers of the volcanic plains material, which formed well after emplacement and solidification of the flows.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; E10; p. 16,149-16,166.
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  • 88
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    Mid-infrared spectroscopy of Pahala ash palagonite and implications for remote sensing studies of Mars (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The mid-IR (7-20 micron range) spectral properties of Pahala ash palagonite and the effect of thin dustings of the palagonite on reflectance characteristics of quartzite and basalt were investigated. Unlike the reflectance of quartzite and basalt, the reflectance of the palagonite is flat and low (1-2 percent). It was found that a dusting of 1-20 micron palagonite particles and 20-250 micron particle clumps, covering 50 percent of the quartzite of the basalt host reduced the quartizite mid-IR reflectance by about 50 percent. The reflectance of the underlying rock was found to be linearly related to the exposed surface area even for extremely small amounts of palagonite (2-100 micron thickness, averaging 5 microns), indicating that mid-IR remote sensing of rocks on Mars will be practical only for dust-free areas.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; E9; p. 14,691-14,699.
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  • 89
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    Viscous shock layer analysis of the Martian aerothermal environment (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 29; 5; p. 633-640.
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  • 90
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    A Mars Environmental Survey mission concept (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Mars Environmental Survey, or 'MESUR' mission presently discussed proceeds by emplacing a network of small stations on the Martian surface. These stations will determine the global seismicity of the planet, to facilitate studies of its internal structure; they will also broaden knowledge of atmospheric and surface meteorology conditions and determine the major and minor elements of surface soil and rock compositions. They are also expected to deepen understanding of Mars' middle and upper atmosphere. Attention is given to the design and operations of the MESUR lander.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars: Past, present, and future; Proceedings of the Conference, Williamsburg, VA, July 16-19, 1991 (A93-12051 02-91); p. 141-152.
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  • 91
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    High-phase-angle observations of Neptune at 2650 and 7500 A - Haze structure and particle properties (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: An analysis is conducted of spatially resolved Voyager 2 Photopolarimeter Subsystem (PPS) observations at 2650 and 7500 A. The continuum absorber that is tropospherically abundant, if confined to the region below the methane haze layer, indicates an optical depth for that layer no greater than 0.8; models in which this optical depth is as large as 3.0 yield too much limb darkening, in the case where the continuum absorber is mixed with both the methane haze and deeper clouds. Tropospheric aerosols are noted to have phase functions with shallow backward lobes.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 99; 2; p. 302-317.
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  • 92
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    Estimation of local planetary gravity fields using line of sight gravity data and an integral operator (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A novel method is presented for mapping line-of-sight gravity data (LOSGD) joining planetary probes and observers during Doppler tracking operations, with a view to geodetic and geophysical applications. LOSGD are in this case mapped as gravity anomalies along a radial direction, at constant altitude, using an inversion procedure in conjunction with a Tikhonov-Arsenine regularization method. The application of different regularization-parameter choices to a synthetic case is followed by application to the real case of Pioneer-Venus orbiter data for Venus' Gula Mons.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 99; 1; p. 202-224.
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  • 93
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    Estimates of absolute flux and radiance factor of localized regions on Mars in the 2-4 micron wavelength region (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: IRTF spectrophotometric observations of Mars obtained during the 1986 opposition are the bases for the present estimates of 2.0-4.15 micron absolute flux and radiance factor values. The bright/dark ratios obtained show a wavelength dependence similar to that observed by Bell and Crisp (1991) in 1990, but the spectral contrast for 1986 is lower than in those observations; this difference could be due to changes in the location, sample are size, and/or suspended atmospheric dust.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 99; 1; p. 42-50.
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    Soil mineralogy and chemistry on Mars - Possible clues from salts and clays in SNC meteorites (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: If the shergottite, nakhlite, and chassignite (SNC) meteorites' parent planet is Mars, then the aqueous precipitates found in them imply that oxidizing, water-based solutions may have been chemically active on that planet over the past 200-1300 million yrs. It is suggested that the mixture of aqueous precipitates found in the SNCs furnish a self-consistent model for the bulk elemental composition of surface sediments at the Viking Lander sites. Further mineralogical and stable-isotope studies of the secondary minerals may establish the limits for biological activity over the last 1300 million years of Mars' water-based chemistry.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 99; 1; p. 28-41.
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    Results from the Magellan mission to Venus (1992)
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    Publication Date: 2011-08-24
    Description: Magellan's radar-mapping mission to Venus has thus far accomplished the mapping of nearly 95 percent of the planet's surface; the 100-m resolution of these data facilitate studies of Venus' geological evolution. Widespread evidence of horizontal compression and extension at many scales is noted. Crustal deformation appears to be distributed across most of the surface. The density distribution of the interior of Venus will be explored in an upcomimg gravity experiment, in which accurate tracking of spacecraft orbital accelerations is used to identify gravity anomalies.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: EOS (ISSN 0096-3941); 73; 2; p. 22.
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  • 96
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    Density waves in Saturn's rings probed by radio and optical occultation - Observational tests of theory (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A parallel examination is conducted of Voyager radio and photopolarimeter occultation observations of the Saturn A ring's density waves. The radio instrument waves exhibit an average -90 deg offset from the dynamical phase. A warping height of about 100-m amplitude can qualtitatively reproduce this phase shift, while preserving the overall model wave shape. These results may be profoundly relevant for satellite-ring torque calculations in Saturn's rings, given the deposition of all of the net torque of the standard model in the first wavelength.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 99; 2; p. 448-467.
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  • 97
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    Optical search for lightning on Neptune (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A search for optical flashes has been conducted to verify the hypothesized identification of whistlers detected by Voyager 2 on Neptune with lightning events. A set of 98 of the best Voyager 2 images of the nightside of Neptune have been processed and searched for optical flashes; no lightning storms were found, despite the image ranges' being as short as those which showed intense lightning storms on Jupiter, and the coverage of the planet by the images being of the order of 94 percent of the surface. Either Neptune's lightning is less visible than that of Jupiter, or it is only one-fourth as frequent.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 99; 2; p. 384-389.
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  • 98
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    Stratospheric ethane on Neptune - Comparison of groundbased and Voyager IRIS retrievals (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Near-simultaneous ground and spacecraft measurements of 12-micron ethane emission spectra during the Voyager encounter with Neptune have furnished bases for the determination of stratospheric ethane abundance and the testing and constraining of Neptune methane-photochemistry models. The ethane retrievals were sensitive to the thermal profile used. Contribution functions for warm thermal profiles peaked at higher altitudes, as expected, with the heterodyne functions covering lower-pressure regions. Both constant- and nonconstant-with-height profiles remain candidate distributions for Neptune's stratospheric ethane.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 99; 2; p. 353-362.
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  • 99
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    The first mission to Mars (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: NASA's first mission to Mars used an Atlas-Agena D launcher, which left Cape Canaveral on November 28, 1964, to place a Mariner probe capable of telemetering back photographs of the Martian surface. After an 8-month flight of 135 million miles, the spacecraft encountered Mars only 500 miles off the aiming point 6000 miles from the Martian surface. Attention is given to NASA-JPL's solving of problems arising after Mariner's separation from the Agena upper stage, using two competing investigative teams.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars: Past, present, and future; Proceedings of the Conference, Williamsburg, VA, July 16-19, 1991 (A93-12051 02-91); p. 29-35.
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    Terraforming earth and Mars (1992)
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    Publication Date: 2011-08-24
    Description: The uncontrolled character of current earth environment changes ascribable to anthropogenic pollutants is presently contrasted with the prospects for a controlled, long-term program of 'terraforming' for Mars, whose culmination could be the introduction of organisms able to thrive in the new Martian environment in carefully designed ways. A detailed discussion is conducted concerning the chemical building-blocks available on Mars for this manner of 'environmental engineering', with frequent reference to comparable and contrasting features of the terrestrial surface, hydrosphere and atmosphere.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars: Past, present, and future; Proceedings of the Conference, Williamsburg, VA, July 16-19, 1991 (A93-12051 02-91); p. 17-26.
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