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  • LUNAR AND PLANETARY EXPLORATION  (20)
  • 1980-1984  (20)
  • 1
    Publication Date: 2019-08-28
    Description: The hypothesis that a part of the lechatellierites which originated by etching from a basic moldavite mass became broken off after deposition of moldavite in the sedimentation layer is advanced. Those found close to the original moldavite were measured for statistical averaging of length. The average length of lechatelierite fibers per cubic mm of moldavite mass volume was determined by measurement under a microscope in toluene. The data were used to calculate the depth of the moldavite layer that had to be etched to produce the corresponding amount of lechatelierite fragments. The calculations from five "fields" of moldavite surface, where layers of fixed lechatelierite fragments were preserved, produced values of 2.0, 3.1, 3.5, 3.9 and 4.5. Due to inadvertent loss of some fragments the determined values are somewhat lower than those found in references. The difference may be explained by the fact that the depth of the layer is only that caused by etching after moldavite deposition.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-TM-77334 , NAS 1.15:77334
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  • 2
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    In:  Other Sources
    Publication Date: 2011-08-19
    Description: Disturbances of the atmosphere at heights of 120 to 40 km by penetration of meteroids of meter and decameter dimensions were examined. Unbiased data on atmospheric penetration of large meteroids was acquired, and their supply of gas and dust components to the middle atmosphere and their connection with the noctilucent clouds were determined.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: International Council of Scientific Unions Middle Atmosphere Program. Handbook for MAP, Vol. 4; p 153-154
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  • 3
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    Publication Date: 2011-08-18
    Description: A bibliography of articles entered into the data base at the Lunar and Planetary Institute Library from November 1982 through January 1983 is presented. An abstract of each article is given. The subjects covered by the articles include: the motion of the moon and dynamics of the earth-moon system: shape and gravity field of the moon; the physical structure of the moon, its thermal and stress history; the morphology of the lunar surface, the origin and stratigraphy of lunar formations, and mapping of the moon; the chemical composition of the moon, lunar petrology, mineralogy, and crystallography; electromagnetic properties of the moon; the planets; and other objects, including asteroids, comets, meteorites, and cosmic dust.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Moon and the Planets (ISSN 0165-0807); 29; 237-327
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  • 4
    Publication Date: 2011-08-18
    Description: Data from the 15 micron band of CO2 readings with the two Viking IR thermal mappers are discussed. Contrasts were observed to be strong between clear and dusty conditions, with a latitudinal gradient and a diurnal amplitude variation in the winter southern hemisphere. Consistency was found in zonal mean temperatures in the absence of dust, with a peak temperature of 180 K at the poles and a diurnal amplitude of 15 K at the equator. Large temperature increases occur in dusty conditions, with global dust storms being present in the northern, but not southern, hemisphere. Estimations of the surface and atmospheric temperatures are calculated in order to derive optical depths from the IR measurements of atmospheric opacity. The optical depth around the whole planet is found to be relatively uniform at any given moment. Finally, the diurnal behavior of the brightness temperature is outlined for 1.4 Mars years.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Advances in Space Research; 2; 2, 19; 1982
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  • 5
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    In:  Other Sources
    Publication Date: 2011-08-18
    Description: It is suggested that existing data on the 1908 Tunguska fall precludes an interpretation of the object as an either active or extinct comet fragment. Because a fireball of the Tunguska mass is not efficiently decelerated by the earth's atmosphere, it would at an entry velocity of about 30 km/sec have had to resist aerodynamic pressures greater than one billon dyn/sq cm before disintegrating. The inherently extremely fragile cometary material could not have survived a load of this magnitude. The data on Type II fireballs with prominent terminal flares are extrapolated, to estimate Tunguska's critical dynamic pressure at the same time of explosion as being of the order of 200 million dyn/sq cm, and its preexplosion velocity as about 10 km/sec, thereby ruling out a comet-like orbit. The Tunguska object is most consistently described as a small Apollo-type asteroid, 90-190 m across.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astronomical Journal (ISSN 0004-6256); 88; Sept
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  • 6
    Publication Date: 2011-08-18
    Description: Calculations of the space charge, ion density, and conductivity in the Venus atmosphere were made. The presence of the cloud particles on Venus causes a profund reduction in the calculated values of the ion density and conductivity compared to the values that are obtained without consideration of the cloud particles. When the cloud particles are included in the calculations, the results for the ion density and conductivity are approximately the same as those of the terrestrial atmosphere at the same pressure-altitude. Because the particles span such a large range of sizes and are abundant over a substantial range of pressure, the space charge varies strongly with altitude and particle size. Differential settling of the particles is expected to produce weak electric fields in the clouds.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 7
    Publication Date: 2011-08-18
    Description: The possibilities of lightning generation on other planets are considered, and the basic conditions that exist in terrestrial clouds during lightning discharges and the various theories of charge separation are reviewed. The properties of terrestrial clouds that produce lightning, the properties of lightning itself, and the fairweather field are first reviewed. The general requirements and the different proposed charging mechanisms for electrification of terrestrial clouds are discussed. The mechanisms of electrical breakdown and whistler production are considered, and recent observations of extraterrestrial lightning and of clouds on other planetary bodies are summarized. Circumstances likely to account for lightning activity on Jupiter and Venus and for electrical activity on Mars and in the rings of Saturn are discussed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 56; 80-115
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  • 8
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    In:  Other Sources
    Publication Date: 2011-08-19
    Description: The near-nucleus dust coma structure of Comet Halley are studied using modern digital image processing techniques on photographs taken in 1910. Recent investigations carried out in conjunction with the Near-Nucleus Studies Net of the IHW to better understand the characteristics and behavior of Comet Halley are reviewed. A new image processing algorithm developed to enhance coma feature boundaries permits their evolution over as many as three days to be followed. The features can be modeled to derive information on the nucleus spin vector, particle sizes, ejection velocities and distribution of emission areas on the nucleus. Useful contributions by observers in the Astrometry Net are also discussed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: JPL Cometary Astrometry; p 14-20
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  • 9
    Publication Date: 2019-01-25
    Description: A new interpretation of the formation of metallic phases in pallasites and nickel-iron meteorites can be made using a non-equilibrium microgravity solidification hypothesis. This hypothesis implies that meteorites were initially large, weightless melts which solidified by radiative cooling. Current theories do not satisfactorily explain the coexistence of equilibrium and metastable phases. The proposed hypothesis accounts for the composition, morphology and coexistence of kamacite, plessite and pearlite within these same meteorites.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Institute The 47th Ann. Meteoritical Soc. Meeting; 1 p
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  • 10
    Publication Date: 2019-01-25
    Description: The effects of gravitational body force must be considered in the formation of extraterrestrial materials such as meteoritic chondrules and lunar glasses. Solidification experiments conducted in microgravity as well as g values greater than Earth's gravitational force have demonstrated that gravitational force can have profound and sometimes unexpected effects upon the way materials solidify and, therefore, upon their physical and mechanical properties. Solutal, thermal and sedimentation effects differ from those experienced on Earth. Because buoyancy forces are reduced, materials of different densities may remain in close proximity. The spherical morphology of chondrules and many lunar glasses may reflect the tendency for free floating liquids to form spherical droplets in a microgravity environment, a form which minimizes surface energy. Under these conditions, surface energy forces dominate gravity forces. The formation of two common chondrule textures, barred and radiating chondrules, can be explained using observations from glass science.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Institute The 47th Ann. Meteoritical Soc. Meeting; 1 p
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