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  • LUNAR AND PLANETARY EXPLORATION  (207)
  • ASTROPHYSICS  (97)
  • 1975-1979  (303)
  • 1970-1974  (1)
  • 1979  (303)
  • 1972  (1)
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  • 1975-1979  (303)
  • 1970-1974  (1)
Year
  • 1
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    The diameter of Pallas from its occultation of SAO 85009 (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The May 29, 1978, occultation of SAO 85009 by Pallas was observed photoelectrically at seven widely spaced sites. The observations are well represented by an elliptical apparent limb profile having semimajor and semiminor axes of 279.5 + or - 2.9 and 262.7 + or - 4.5 km, respectively. Combining these results with published information on the light curve and rotational pole position, Pallas's mean diameter is found to be 538 + or - 12 km, which yields a mean density for Pallas of 2.8 + or - 0.5 g/cu cm and a visual geometric albedo of 0.103 + or - 0.005. The diameter of Pallas as determined from this occultation is significantly smaller than the values derived by radiometric, polarimetric, and double-image techniques.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astronomical Journal; 84; Feb. 197
    Format: text
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  • 2
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    Evidence for lightning on Venus (1979)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Evidence for lightning on Venus obtained by the Pioneer Venus 1 Orbiter is presented. The first indications of lightning were detected by the electric field detector on board the Orbiter when the spacecraft periapsis, which is well within the ionosphere, moved into the night side of the planet. Impulsive wave signals were primarily detected at altitudes less than 25 km, and were found to be strongest at frequencies corresponding to propagation in the whistler mode, occurring at an average rate of about 0.5/sec. The signals were often observed during intervals of low and variable electron densities. It is tentatively concluded on the basis of the above observations that the impulsive events were caused by Venusian lightning.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 279; June 14
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  • 3
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    Stellar model chromospheres. XI - A survey of Ca II lambda 8542 line profiles in late-type stars of differing chromospheric activity (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Keywords: ASTROPHYSICS
    Type: PB80-144215 , Astrophysical Journal Supplement Series; 41; Nov. 197
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  • 4
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    Absorption of whistler mode waves in the ionosphere of Venus (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: It is shown that whistler mode waves from the ionosheath of Venus are absorbed by Landau damping at the dayside ionosphere boundary. This process heats the ionospheric electrons and it may provide an important energy input into the dayside ionosphere. Cyclotron damping of the waves does not occur in the same region. However, Landau damping of ionosheath waves is apparently not an important energy source in the nightside ionosphere. Impulsive events in the nightside ionosphere seem to fall into two classes: (1) lightning signals (near periapsis) and (2) noise, which may be caused by gradient or current instabilities.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 205; July 6
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  • 5
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    Regolith development and evolution on asteroids and the moon (1979)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Early descriptions of regoliths on small bodies were devised to account for observations of asteroids (Chapman 1971, 1976) and the gas-rich meteorites (Anders 1975). Lack of agreement between these approaches prompted Housen et al. (1978, 1979) to examine the problem in detail. The resulting model predicted that moderate-sized (100-300 km) asteroids should evolve regoliths up to a few kilometers deep which could be source regions of gas-rich meteorites. Smaller objects should have regoliths ranging from dust coatings to meters-thick layers depending on the strength of the object. The earlier model could not treat asteroids larger than 300 km in diameter. The model, now modified to treat larger-sized objects, predicts regolith depths, on asteroids larger than 300 km, which decrease with increasing size. A regolith depth of 7 m is predicted for the lunar maria in reasonable agreement with the observed depths of 5 m.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 6
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    The asteroids - Accretion, differentiation, fragmentation, and irradiation (1979)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Various types of meteorites have experienced processes of condensation, accretion, metamorphism, differentiation, brecciation, irradiation and fragmentation. A typical view of meteorite formation has been that the processes following accretion take place in a few asteroidal-sized (approximately 100 km) objects. Discovery of decay products of now extinct Al-26 and Pd-107 in meteorites, discovery of isotopic heterogeneity among meteorite types, re-analysis of meteorite cooling rates, and continuing study of meteoritic compositions have led some meteoriticists to conclude that meteorites obtained their chemical, isotopic, and some textural characteristics in objects initially less than 10 km in diameter. Such a scenario, which is described in this paper, raises the possibility that some of these small planetesimals may have been 'condensation nuclei' for the formation of comets as well as the precursors of asteroids.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 7
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    Voyager 1 photopolarimeter experiment and the phase curve and surface microstructure of Ganymede (1979)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Results are reported for optical-wavelength photopolarimetry of Ganymede from Voyager 1. A phase coefficient of 0.011 + or - 0.001 mag/deg and an opposition effect of 0.17 + or - 0.03 mag are derived. It is shown that Ganymede's surface is probably more porous than Callisto's and that micrometeoroids may continuously roughen the surface of Ganymede.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 280; Aug. 30
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  • 8
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    Balloon-borne ultraviolet stellar spectrograph. I - Instrumentation and observation. II - Highlights of first observational results (1979)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: A dual star-tracking system and a system including a telescope, an echelle spectrograph, and a SEC vidicon are the chief components of the Balloon-borne Ultraviolet Stellar Spectrograph (BUSS), which has flown four successful missions. The BUSS missions have yielded 81 spectra for 56 stars, recorded with a resolution of 0.1 A in the wavelength range from 2200 to 3400 A. BUSS observations include: profiles of Mg II lines indicating considerable mass flow in early-type supergiants; Mg II features suggesting a cool expanding outer shell above a hotter chromosphere; emission features in Zeta Tau (a shell star) indicating infalling material; and emission features of the Be star Phi Per suggesting mass outflow.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 230
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  • 9
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    Ar-40/Ar-39 age of the Shergotty achondrite and implications for its post-shock thermal history (1979)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Ar-40/Ar-39 measurements are used to determine the age of the Shergotty achondrite and the chronology of the shock event responsible for the complete conversion of its plagioclase to maskelynite is discussed. Apparent ages are found to vary between 240 and 640 million years for the whole rock sample, with a plateau age of 254 million years for a maskelynite separate. The Rb-Sr age of 165 million years determined by Nyquist at al (1978) suggests that the maskelynite as well as the whole rock was incompletely degassed. Argon diffusion characteristics indicate a post-shock cooling time greater than 1000 years and a burial depth greater than 300 m for a thermal model of a cooling ejecta blanket of variable thickness. It is concluded that the shock event which degassed the argon and reset the Rb-Sr systematics occurred between 165 and 250 million years ago when the parent body experienced a collision in the asteroid belt.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta; 43; July 197
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  • 10
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    Nature of the ultraviolet absorber in the Venus clouds - Inferences based on Pioneer Venus data (1979)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Several photometric measurements of Venus made from the Pioneer Venus orbiter and probes indicate that solar near-ultraviolet radiation is being absorbed throughout much of the main cloud region, but little above the clouds or within the first one or two optical depths. Radiative transfer calculations were carried out to simulate both Pioneer Venus and ground-based data for a number of proposed cloud compositions. This comparison rules out models invoking nitrogen dioxide, meteoritic material, and volatile metals as the source of the ultraviolet absorption. Models involving either small (approximately 1 micrometer) or large (approximately 10 micrometers) sulfur particles have same serious difficulties, while ones invoking sulfur dioxide gas appear to be promising.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 205; July 6
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