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  • Inorganic Chemistry  (2.098)
  • LUNAR AND PLANETARY EXPLORATION  (1.805)
  • 1985-1989  (1.224)
  • 1980-1984  (2.679)
  • 1925-1929
  • 1988  (1.224)
  • 1983  (1.254)
  • 1980  (1.425)
Sammlung
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  • 1985-1989  (1.224)
  • 1980-1984  (2.679)
  • 1925-1929
Jahr
  • 1
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    The Lunar Orbital Prospector (1988)
    In:  CASI
    Details
    Publikationsdatum: 2005-07-19
    Beschreibung: The Moon is a body rich in natural resources and full of intriguing scientific questions, and it will most certainly play a central role in the growth of near-Earth and deep space ventures of the twenty-first century. The LOP mission is an example of one way to catalog the Moon's natural resources and to answer lunar science questions in parallel. In a realistic planetary exploration program, this mission must compete with other interesting planetary missions and therefore the LOP must be as low cost and adaptable as possible. This flexibility is reflected in the LOP's heavy design emphasis on modularity. The LOP mission can easily be expanded to include new technologies, and additional orbiters could be launched into lunar orbit to provide a constellation of remote-sensing platforms. This design thus projects a broad range of possibilities for continued lunar exploration in the next century.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: USRA, NASA(USRA University Advanced Design Program Fourth Annual Summer Conference; p 145-151
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  • 2
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    Design of a lunar transportation system (1988)
    In:  CASI
    Details
    Publikationsdatum: 2005-07-19
    Beschreibung: The establishment of lunar bases is the next logical step in the exploration of space. Permanent lunar bases will support scientific investigation, the industrialization of space, and the development of self-sufficiency on the Moon. Scientific investigation and research and development would lead to applications utilizing lunar material resources. By utilizing these resources, the industrialization of space can become a reality. The above two factors coupled with the development of key and enabling technologies would lead to achievement of self-sufficiency of the lunar base. Attention was focused on specific design(s) to be pursued during subsequent stages in advanced courses. Some of the objectives in the project included: (1) minimizing the transportation of construction material and fuel from earth, or maximizing the use of the lunar material; (2) use of novel materials and light weight structures; (3) use of new manufacturing methods and technology such as magnetically levitated, or superconducting materials; and (4) innovative concepts of effectively utilizing the exotic lunar conditions, i.e. high thermal gradients, lack of atmosphere, zero wind forces, and lower gravity, etc.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: USRA, NASA(USRA University Advanced Design Program Fourth Annual Summer Conference; p 89-92
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  • 3
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    Measurements of reflectance spectra of ion-bombarded ice and application to surfaces in the outer solar system (1988)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-19
    Beschreibung: The first results of laboratory measurements of the wavelength dependence of the alternation of the visible reflectance of H2O ice irradiated by keV ions are presented. When the implanted species is chemically neutral, absorption is slightly enhanced below 0.55 micron. For an incident species containing sulfur, a strong absorption feature is produced at 0.4 micron, probably corresponding to S3. This occurs at too large a wavelength to account for the absorption feature observed at Europa by Voyager and therefore casts doubt on the recent interpretation of the reflectance data of Europa.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Nature (ISSN 0028-0836); 333; 240
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  • 4
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    Surficial textures of the Galilean satellites (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The observations of the Galilean satellites of Jupiter obtained with the IUE have been analyzed as a function of solar phase angle. By fitting the measurements to a shadowing model, comparative descriptions of the microtextures of the optically active portion of the surfaces of the satellites are derived. Important differences among the satellites and between leading and trailing hemispheres of individual satellites result from the different processes of meteoritic bombardment, magnetospheric interaction, and geological resurfacing that operate in the Jovian system. Io and Callisto have the most tenuous upper regoliths, whereas the surface of the leading side of Europa is the most compact.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Nature (ISSN 0028-0836); 333; 148-151
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  • 5
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    Thermal structure of the ionosphere of Mars - Simulations with one- and two-dimensional models (1988)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-19
    Beschreibung: Heat flux saturation effects are included in the present one- and two-dimensional models of the Martian upper ionosphere's thermal structure. The inclusion of small upper boundary and volume heat sources is found to yield satisfactory simulations of the dayside ion temperature observation results obtained by Viking 1's retarding potential analyzers. It is noted that the plasma flow-transport of heat from the dayside to the nightside makes no contribution to the ion and electron temperatures that have been calculated for the nightside.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 74; 357-364
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  • 6
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    Deformational models of rifting and folding on Venus (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Features of presumed tectonic origin on Venus are reviewed, and lithospheric strength envelopes are derived based on laboratory measurements of the deformational properties of crustal and subcrustal rocks, extrapolated to conditions appropriate to Venus. Models for rifting and folding are developed that use this lithospheric structure and take into account both brittle and ductile yielding as well as finite elastic strength. For both rifting and folding, structures with characteristic widths and spacings are predicted whose size depends on the thickness of the lithosphere, density contrast, and elastic properties of the layer. Finally, the model predictions are compared with the widths and spacings of observed tectonic features, and it is concluded that they are consistent with a relatively strong mantle layer separated from a thin brittle surface layer by a ductile lower crust. These results allow constraints to be placed on the crustal thickness and thermal gradient on Venus.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 93; 4759-477
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  • 7
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    Evolution of a steam atmosphere during earth's accretion (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The evolution of an impact-generated steam atmosphere around an accreting earth is presently modeled under the assumption of Safronov (1978) accretion, in a scheme that encompasses the degassing of planetesimals on impact, thermal blanketing by the steam atmosphere, surface-to-interior water exchange, the shock heating and convective cooling of the earth's interior, and hydrogen escape due both to solar EUV-powered planetary wind and impact erosion. The model yields four distinct classes of impact-generated atmospheres: the first, on which emphasis is placed, has as its salient feature a molten surface that is maintained by the opacity of a massive water vapor atmosphere; the second occurs when the EUV-limited escape exceeds the impact degassing rate, while the third is dominated by impact erosion and the fourth is characterized by an atmosphere more massive than any thus far encountered.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 74; 62-97
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  • 8
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    On the origin of Venus' atmosphere - Possible contributions from simple component mixtures and fractionated solar wind (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: It is suggested that while an origin of the volatiles of the Venus atmosphere as a single, fractionated component derivable from the solar wind can account for Ar, Kr, and Xe relative abundances, it does so only with an excess of C, and perhaps of N. A similarity is noted in relative abundances between Venus volatiles and fractionated solar wind gases in the lunar regolith which implies that such a lunar-type component is a major contributor to Venus' volatiles. A variety of Venus atmosphere models is considered; these fail to explain the low Ne/Ar ratio on Venus.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 74; 3-20
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  • 9
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    Source of the Australasian tektite strewn field - A possible off-shore impact site (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Although there is a preponderance of evidence that tektites were formed by asteroid impacts on the earth, no source crater has been found for the largest and youngest of the strewn fields - the Austalasian strewn field. A combined Seasat/Geos 3 altimeter data set of sea surface heights in the northern portion of the Australasian strewn field has been examined for negative gravity anomalies on the continental shelf and slope which might be related to the source crater for these tektites. A large negative anomaly called the Qui Nhon Slope Anomaly is a sea surface depression of approximately 1.5 meters over an area of 100 km diameter. It corresponds to a gravity anomaly of about -50 mgal. It is proposed that this anomaly may be due to the impact structure that produced the Australasian strewn field.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Geophysical Research Letters (ISSN 0094-8276); 15; 357-360
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  • 10
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    The solar wind control of Jupiter's broad-band kilometric radio emission (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Observations of the solar wind close to Jupiter are compared with the broad-band kilometric radio emission (bKOM), using data recorded by Voyager 1 and Voyager 2 during 1979. The lower bKOM frequencies, less than about 300 kHz, are found to correlate with the solar wind density and pressure and with the interplanetary magnetic field (IMF) magnitude during periods when there is a well-defined magnetic sector structure. The results suggest that lower frequency bKOM events are most likely to occur after a sector boundary has passed Jupiter during the period when the solar wind density and the IMF magnitude are increasing towards the sector center. The average bKOM energy per Jovian rotation tends to have lower values soon after the sector center has passed. Higher-frequency/higher-energy bKOM emission may be contaminated by hectometric emission (HOM) and differently correlated with solar activity. The solar wind control may also be obscured by some stronger control. It is suggested that electron density fluctuations in the Io torus, where the source is believed to be located, may be responsible for variations in the beaming and hence variations in the observed emission.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Astronomy and Astrophysics (ISSN 0004-6361); 192; 1-2,; 354-359
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  • 11
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    Large impact basins and the mega-impact origin for the crustal dichotomy on Mars (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The hypothesis that the crustal dichotomy on Mars is due to a single giant (mega) impact early in Martian history is tested by determining the number of 'missing' basins, the difference between the observed number of large impact basins on Mars and the number expected from a 1/D-squared distribution. If the Borealis Basin was the largest member of a 1/D-squared impact population, a large number of 'missing' basins is expected which is too large to be hidden by the younger surface units. If Chryse is the largest member of a 1/D-squared impact population, the more modest number of 'missing' basins could be confined to areas of Mars that have been resurfaced or reworked by subsequent geologic processes.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Geophysical Research Letters (ISSN 0094-8276); 15; 229-232
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  • 12
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    Thermal emission from Saturn's rings at 380 microns (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Two different techniques have been used to derive the Saturn disk's ring brightness temperatures from 380-micron observations: (1) comparisons of these wide-beam observation disk-ring system results with those obtained for an earlier epoch, when the rings were edge-on, then differencing the two measurements to obtain a value for the rings' contribution; and (2) ring contribution resolution during scanning along the disk-ring plane, to yield a B-ring brightness temperature of 39 + or - 8 K at 380 microns. The results obtained indicate a gradual decrease of observed ring brightness temperature from the IR to the radio wavelength range.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 574-583
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  • 13
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    Superposed ridges of the Hesperia Planum area on Mars (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Mare ridges of the Hesperia Planum area form linear, reticular and circular structures. The main factors effective in mare ridge formation have been: (1) a large areal, or maybe even global, shortening and compression, (2) major crustal tectonics, and (3) the moderation of tectonic movements by the megaregolith discontinuity layer(s) between surface lavas and the bedrock leaving the compressional thrust to dominate over other fault movements in surface tectonics.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Earth, Moon, and Planets (ISSN 0167-9295); 40; 71-99
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  • 14
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    Analysis of Pioneer Venus Orbiter ultraviolet spectrometer Lyman alpha data from near the subsolar region (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Pioneer Venus Orbiter ultraviolet spectrometer data from 20 orbits which span 3 years have been analyzed to determine the atomic hydrogen number density and vertical flux at the exobase as a function of solar zenith angle, F(10.7) index, and spacecraft latitude. From 1979 through 1981, the exobase number density n(c) and flux phi(c) are remarkably constant at n(c) = 6.0 + or - 1.5 x 10 to the 4th/cu cm and phi(e) = 7.5 + or - 1.5 x 10 to the 7th/sq cm per s in the subsolar region. The integrated vertical column density above 110 km is 3.6 + or - 1 x 10 to the 13th/sq cm. An empirical relationship is determined between the line center solar flux at H Lyman alpha, piF(0), and the F(10.7) index.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 93; 1766-177
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  • 15
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    Voyager at Uranus (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The findings made in the Voyager flyby past Uranus are reviewed. The spacecraft is described, and the preparations for the Uranus encounter are recalled. The encounter characteristics are presented, and the characteristics of the Uranian atmosphere and interior, magnetic field, rings, and satellites are discussed.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: (ISSN 0007-084X); 41; 49-62
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  • 16
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    Neptune radio emission - Predictions based on planetary scaling laws (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: In this paper a prediction is advanced concerning Neptune's low-frequency radio emission based on the radiometric Bode's law for radio planets in combination with the magnetostrophic scaling law for magnetized planets. The total emitted radio power is predicted to be about 1.6 x 10 to the 7th W, very nearly the same as that predicted and observed for Uranus. Possible emission spectral shapes, based on Saturn and earth-like models, are shown. Using these models, the radio emission frequency range is predicted to extend from approximately 100 to just over 1000 kHz, with a spectral peak between 350 and 500 kHz. If radiation is beamed approximately in the sunward direction, Neptune should be detectable by the planetary radio astronomy experiment onboard the Voyager spacecraft sometime between 45 and 90 days before closest approach. This detection is likely to represent the first direct evidence of a Neptune magnetic field. Possible implications for Neptune's magnetosphere with regard to the time of first detection are discussed.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Geophysical Research Letters (ISSN 0094-8276); 15; 114-1117
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  • 17
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    High resolution images of Venus from ground-based radar (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The Goldstone Deep Space Station ground-based synthetic aperture radar system has been used to obtain radar images of Venus with resolutions of close to 1.3 km. Observations were made at 12.5 cm wavelength using circular polarization. From 12 days of observations during the 1986 inferior conjunction, three images have been selected for initial processing. The images show remarkable surface features including craters, ridges, and regions of high Fresnel reflectivity in the plains region.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Geophysical Research Letters (ISSN 0094-8276); 15; 577-580
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  • 18
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    High-temperature shock formation of N2 and organics on primordial Titan (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Theoretical models suggest that the initial form of nitrogen in Titan's atmosphere may have been NH3. The possible importance of strong shocks produced during high-velocity impacts accompanying the late stages of accretion are investigated as a method for converting NH3 to N2, of which Titan's atmosphere is now primarily composed. The focused beam of a high-power laser is used to simulate the effects of an impact in Titan's atmosphere. For mixtures of 10, 50, and 90 percent NH3, yields of 0.25, 1, and 6 x 20 to the 17th molecules of N2 per joule, respectively, were obtained. It is also found that the yield of HCN is comparable to that for N2. Several other hydrocarbons are produced, many with yields in excess of theoretical high-temperature-equilibrium models. The above yields, when combined with models of the satellite's accretion, result in a total N2 production comparable to that present in TItan's atmosphere and putative ocean.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Nature (ISSN 0028-0836); 332; 520-522
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  • 19
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    Charged particle depletion surrounding Saturn's F ring - Evidence for a moonlet belt? (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: An improved model of the Saturn magnetosphere and of the locations of known moons and rings is invoked in the present reconsideration of Pioneer 11 observations of five abrupt depletions in the flux of trapped magnetospheric electrons within a 2000-km-wide band around the F ring. It is inferred that the observed depletions of charged particles are caused by clumps of material with low optical depth; it is further hypothesized that these clumps are composed of regolith ejecta, are generated by collisions occurring within a belt of unseen, moonlet-scale (or smaller) objects occupying the entire radial region between Pandora and Prometheus. Attention is given to a self-consistent scenario in which these debris clouds are created, longitudinally spread, swept up onto belt object surfaces, and then thrown off by a subsequent collision.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 74; 284-324
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  • 20
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    Planetographic clustering of low-altitude impulsive electric signals in the night ionosphere of Venus (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: This paper presents maps of the locations of electromagnetic signals, presumably caused by lightning, which were observed at 730 Hz during the first three nighttime observing seasons of Pioneer Venus Orbiter when the spacecraft reached altitudes low enough to detect the signals. The maps show that there are specific 'active regions' of enhanced signal occurrence, and that at least some of these active regions appear to remain fixed in planetographic coordinates from year to year.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Nature (ISSN 0028-0836); 331; 591-594
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  • 21
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    'Domestic' origin of opaque assemblages in refractory inclusions in meteorites (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Experimental studies indicate that opaque assemblages rich in refractory siderophile elements were formed within host calcium- and aluminum-rich inclusions (CAIs) by exsolution, oxidation and sulphidization of homogeneous alloys, rather than by aggregation of materials in the solar nebula before the formation of CAIs. These opaque assemblages are thus not the oldest known solid materials, as was once thought, and they do not constrain processes in the early solar nebula before CAI formation. Instead, the assemblages record the changing oxygen fugacity experienced by CAIs during slow cooling in nebular and/or planetary environments.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Nature (ISSN 0028-0836); 331; 405-409
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  • 22
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    Are there carbonate deposits in the Valles Marineris, Mars? (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The precipitation of 30 mbar of Martian atmosphere CO2 as carbonates in lakes is suggested to be the source of thick sequences of layered deposits found in the Valles Marineris. Support is adduced for this scenario from processes occurring in the perennially frozen dry valley lakes of Antarctica, where the lake water is supersaturated with atmospheric gases. Atmospheric CO2 would have accumulated in such Martian lakes as temperatures fell, and the presence of an insulating ice cover would have allowed liquid water to exist.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 73; 142-148
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  • 23
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    Interactions of planetesimals with protoplanetary atmospheres (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The 'core instability' mechanism presently postulated for the interaction of planetesimals with the envelopes of growing giant planets involves core growth through the accretion of solid bodies in the solar nebula; the core thereby becomes more effective in the gravitational attraction of gas from the surrounding nebula into an envelope, until a runaway accretion stage is reached. Two-body trajectory curves of planetesimals through this envelope are computed which demonstrate the depth of penetration and the cross-sections for capture of icy and rocky planetesimals.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 73; 163-179
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  • 24
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    How climate evolved on the terrestrial planets (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: It is argued that the difference in the climates of Venus, earth, and Mars is due largely to differences in their ability to cycle CO2 between the crust and atmosphere. It is suggested that the earth has always had a moderate climate primarily because its cycling mechanism increases the amount of CO2 in the atmosphere when the surface of the planet cools and reduces the amount when the ground temperature rises. Mars is now frozen because it has lost the ability to cycle the gas back into its atmosphere, and Venus is a hothouse because it has no way of removing CO2 from its atmosphere.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Scientific American (ISSN 0036-8733); 258; 90-97
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  • 25
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    The tectonics of Mercury (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The probable tectonic history of Mercury and the relative sequence of events are discussed on the basis of data collected by the Mariner-10 spacecraft. Results indicate that Mercury's tectonic activity was confined to its early history; its endogenic activity was principally due to a small change in the shape of its lithosphere, caused by tidal despinning, and a small change in area caused by shrinkage due to cooling. Exogenic processes, in particular the impact activity, have produced more abundant tectonic features. Many features associated with the Caloris basin are due to loading of Mercury's thick lithosphere by extrusive lavas or subsidence due to magma withdrawal. It is emphasized that tectonic features observed on Mercury yield insight into the earliest tectonic events on planets like Mars and, perhaps, the earth, where subsequent events obscured or erased the most ancient tectonic records.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
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  • 26
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    Surface composition of Mercury from reflectance spectrophotometry (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The controversies surrounding the existing spectra of Mercury are discussed together with the various implications for interpretations of Mercury's surface composition. Special attention is given to the basic procedure used for reducing reflectance spectrophotometry data, the factors that must be accounted for in the reduction of these data, and the methodology for defining the portion of the surface contributing the greatest amount of light to an individual spectrum. The application of these methodologies to Mercury's spectra is presented.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
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    Meteorite regolithic breccias (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: In addition to endogenic processes such as heating and aqueous activity, meteorite parent bodies were subjected also to exogenic processing brought about by the impact of the other solar-system objects. Such impacts can produce a variety of effects, ranging from shock metamorphism of individual mineral grains to production of breccias; i.e., rocks consisting of mixtures of disparate lithic units. The present paper reviews recent studies of such breccias, which have generated significant information about the accretional growth of parent bodies, as well as their evolution, composition, stratigraphy, and geological processing.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
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  • 28
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    Extended sodium exosphere of the moon (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Sodium emission has been observed up to 1200 km above the subsolar limb of the moon at third quarter. The intensity of the emission is far in excess of that predicted from the scale height and surface density derived previously from measurements of sodium emission at low altitudes above the lunar surface. This can be explained by assuming that there are both 'hot' and 'cold' components of the lunar sodium exosphere.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Geophysical Research Letters (ISSN 0094-8276); 15; 1515-151
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  • 29
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    Io - Evidence for silicate volcanism in 1986 (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Infrared observations of Io during the 1986 apparition of Jupiter indicate that a large eruptive event occurred on the leading side of Io on August 7, 1986, UT. Measurements made at 4.8, 8.7, and 20 micrometers suggest that the source of the event was about 15 kilometers in radius with a model temperature of about 900 K. These measurements indicate that high-temperature volcanic activity on the leading side of Io may be more frequent than previously thought. The inferred temperature is significantly above the boiling point of sulfur in a vacuum (715 K) and thus constitutes strong evidence for active silicate volcanism on the surface of Io.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Science (ISSN 0036-8075); 242; 1280-128
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  • 30
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    Stratospheric composition measurements of earth and Titan using high-resolution tunable diode laser spectroscopy (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Field and laboratory measurements of species of atmospheric interest made as part of the JPL diode laser spectroscopy program are presented. Stratospheric measurements of NO2, NO, CO2, and H2O made in November 1985 using the BLISS instrument are reported, together with recent laboratory measurements of spectral line parameters of HNO3 and HO2NO2. In addition, a novel diode laser instrument concept for the in situ sensing of Titan's atmosphere is described for the Saturn Orbiter/Titan Probe (SOTP) Cassini Mission.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Quantitative Spectroscopy and Radiative Transfer (ISSN 0022-4073); 40; 239-248
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  • 31
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    Spectra of van der Waals complexes (dimers) with applications to planetary atmospheres (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Spectral features observed in the atmosphere of Titan by the Voyager IR experiment have been attributed to weakly bound complexes of N2 and H2, dominant and minor constituents, respectively. The abundance of H2-N2 dimers there was computed. Current calculations include quantitative spectral line positions and intensities for N2-Ar and CO2-CO2 relating to Titan and Earth, and to Mars and Venus, respectively. This work suggests applications to spectra of planetary atmospheres obtained in spacecraft missions.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Quantitative Spectroscopy and Radiative Transfer (ISSN 0022-4073); 40; 177-184
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  • 32
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    Zonally symmetric response to atmospheric tidal forcing in the dusty Martian atmosphere (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The paper presents a steady state, zonally symmetric response of an atmospheric circulation to the combined effects of the very large zonal-mean diabatic heating and thermotidal forcing thought to exist in the dusty Martian atmosphere during one of its episodic global dust storms. The zonal-mean components of the tidal flux-convergences of momentum and heat are computed using an existing classical atmospheric tidal model constrained by the surface pressure observations at the two Viking Lander sites on Mars. A nearly inviscid two-dimensional model is used to compute the zonally symmetric response to the computed tidal flux-convergences and to the zonal-mean heating of the airborne dust. The results are compared with data from the Viking missions.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of the Atmospheric Sciences (ISSN 0022-4928); 45; 2469-248
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  • 33
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    Lightning production of hydrocarbons and HCN on Titan - Laboratory measurements (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Experimental measurements have been obtained for the chemical yields of hydrogen cyanide, acetylene, ethylene, ethane, and propane from simulated lightning discharges, in order to ascertain whether lightning in the troposphere of Titan may be contributing to the hydrocarbon inventory. A comparison of these results with those obtained on the basis of thermodynamic equilibrium considerations shows substantial discrepancies and implies that thermodynamic equilibrium theories are inadequate. The production of ethylene by lightning and its subsequent stratospheric diffusion nevertheless appears to be one reasonable mechanism.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 76; 125-134
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  • 34
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    Mars - Satellite and ring search from Viking (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Viking Orbiter 1 imaging data were used in a search for possible satellites and rings of Mars in 1980, giving attention to a region within the Phobos orbit and + or - 350 km about the Martian equatorial plane. After picture processing, no images other than stars and Phobos itself were found to be a few brightnesses (or more) above their surrounding, as would be expected in the case of a point-spread, 'smeared' image of either satellites or rings. There is therefore no evidence of any such phenomenon in the 78 pictures studied.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 76; 160-162
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  • 35
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    Pressure-induced absorption coefficients for radiative transfer calculations in Titan's atmosphere (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The semiempirical theory of Birnbaum and Cohen (1976) is used to calculate the FIR pressure-induced absorption (PIA) spectra of N2, CH4, N2 + Ar, N2 + CH4, and N2 + H2 under conditions like those in the Titan troposphere. The results are presented graphically and compared with published data from laboratory measurements of PIA in the same gases and mixtures (Dagg et al., 1986; Dore et al., 1986). Good agreement is obtained, with only a slight underestimation of PIA at 300-400/cm in the case of CH4. The absorption coefficients are presented in tables, and it is suggested that the present findings are of value for evaluating the effects of tropospheric clouds on the Titan FIR spectrum and studying the greenhouse effect near the Titan surface.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 75; 245-254
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  • 36
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    Methane rain on Titan (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The atmosphere of Titan is characterized by means of model computations based on Voyager IRIS IR spectra and published data from laboratory determinations of absorption coefficients and cloud refractive indices. The results are presented in tables and graphs, and it is pointed out that the presence of Ar is not required in the model. Particular attention is given to the role of CH4, which is found to form patchy clouds (with particle radii of 50 microns or greater and visible/IR optical depths of 2-5) at altitudes up to about 30 km. The mechanisms by which such rain-sized particles could form are discussed, and it is suggested that the observed 500-600/cm spectrum is affected much less by the CH4 clouds than by H2 or variations in the temperature of the high-altitude haze.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 75; 255-284
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  • 37
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    Impact-driven supply of sodium and potassium to the atmosphere of Mercury (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The Mercury atmosphere is supplied with sodium atoms from both impacting meteoroids and the impacted regolith; the production of vaporized sodium due to such impact varies with the instantaneous distance of Mercury from the sun, in a way that differs from the distance-dependence of those source-and-sink processes driven by solar radiation. Such impact-driven vaporization will yield the Na/K ratio noted in the Mercury atmosphere only if both the meteoroids and the regolith of the planet are deficient in K relative to other solar system objects sampled, other than comets.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 75; 156-170
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  • 38
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    Enceladus - Implications of its unusual photometric properties (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Voyager 1 and 2 images are used to ascertain the photometric properties of Enceladus up to a 43-deg phase angle. The lack of correlation noted between spectrophotometric properties and terrain type indicates that optical characteristics result from a recently-deposited, ubiquitous surface layer that may have originated on the E-ring of Saturn. Enceladus' distinctive phase and photometric functions can be accounted for by the high degree of surface multiple scattering; observations to date indicate that the Enceladus regolith's textural characteristics are similar to those of other icy satellites of Saturn.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 75; 113-126
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  • 39
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    Large-amplitude photometric variations of Nereid (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Photometric UVBRI and astrometric data on Nereid were collected in June, 1987 using the 0.9-m telescope and CCD camera at the Cerro Tololo Inter-American Observatory. Four astrometric positions and UVBRI reflectances spanning eight days were obtained. From these data, an unusual reflectance spectrum for Nereid was determined. Variability of Nereid was observed in all bandpasses, with an amplitude greater than 1.5 mag and a probable period of between 8 and 24 hr.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Nature (ISSN 0028-0836); 333; 436-438
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  • 40
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    Aeolian weathering of Venusian surface materials - Preliminary results from laboratory simulations (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: An attempt is made to duplicate the atmospheric temperature, pressure, and approximate gas composition of all surface elevations on Venus by means of a simulator environment in which particles are impacted against rock targets as a way of studying planetary aeolian processes. While particles are abraded even at the low impact velocities envisioned for Venus, the same particles do not generate basaltic rock abrasion for impact velocities lower than 1 m/sec; comminution debris is instead transferred onto rock surfaces to form an accretion layer. These phenomena are seen as functions of the greater than 660 K temperatures encountered.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 74; 495-515
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  • 41
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    Runaway and moist greenhouse atmospheres and the evolution of earth and Venus (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: For the case of fully moisture-saturated and cloud-free conditions, the present one-dimensional climate model for the response of an earthlike atmosphere to large solar flux increases notes the critical solar flux at which runaway greenhouse (total evaporation of oceans) occurs to be 1.4 times the present flux at the earth's orbit, almost independently of the CO2 content of the atmophere. The value is, however, sensitive to the H2O absorption coefficient in the 8-12 micron window. Venus oceans may have been lost early on due to rapid water vapor photodissociation, followed by hydrogen escape into space.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 74; 472-494
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  • 42
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    Vacuum weathering of sulfur - Temperature effects and applications to Io (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The effect of surface temperature on the initial transient and subsequent steady-state behavior of the vacuum-sublimation rate and the UV/visible spectral reflectance of frozen sulfur has been investigated. Surface temperature is found to be the dominant parameter controlling the rate of vacuum weathering of sulfur. The present results suggest that any freshly-frozen sulfur deposits on Io at typical Io hotspot temperatures should display major transient changes in color in a matter of hours to days. It is noted that these rapid changes in spectral reflectivity should be readily detectable by future high-resolution synotopic observations of Io spectrum in the UV/visible.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Geophysical Research Letters (ISSN 0094-8276); 15; 697-700
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  • 43
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    Free and forced modes in the Martian atmosphere (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Computations are conducted for the periods of free modes in the Martian atmosphere with a view to the short atmospheric radiative damping time and the seasonal and interannual variation of globally representative temperatures, both of which differ from their terrestrial counterparts by an order of magnitude. Attention is given to the possibility of atmospheric resonance and the efficient excitation (or even the resonant amplification) of forced modes. A thermally-forced diurnal Kelvin wave is recommended as the most reasonable of several alternative explanations of the short-period transient mode that occurs just before, or during, Mars' great episodic dust storms.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 93; 9452-946
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    Ti(3+) in meteoritic and synthetic hibonite (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: This paper describes the first direct determination (performed by electron spin resonance spectroscopy) of Ti(3+) in hibonite from inclusion SH-7 of the Murchison C2 chondrite and in synthetic hibonites of four compositions, three of which corresponded to the compositions of blue hibonites and one to that of an orange hibonite. The Ti(3+) concentration in the hibonite from SH-7 was found to range from 0.35 to 0.44 percent, while the Ti(3+) contents in three synthetic blue hibonites ranged from 0.02 to 0.64 percent. Orange hibonite contained no Ti(3+), supporting an earlier conclusion that the orange-to-blue transition is associated with the presence of Ti(3+). At constant temperature and oxygen fugacity, the Ti(3+)/Ti(4+) ratio in synthetic hibonites was found to increase with decreasing V, but was not strongly dependent on bulk Ti. Fe and Cr contents did not have a significant effect on the amount of Ti(3+).
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 52; 1479-149
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  • 45
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    Remanent magnetism at Mars (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: It is shown that a strong case can be made for an intrinsic magnetic field of dynamo origin for Mars earlier in its history. The typical equatorial magnetic field intensity would have been equal to about 0.01-0.1 gauss. The earlier dynamo activity is no longer extant, but a significant remanent magnetic field may exist. A highly non-dipole magnetic field could result from the remanent magnetization of the surface. Remanent magnetization may thus play an important role in the Mars solar wind interactions, in contrast to Venus with its surface temperatures above the Curie point. The anomalous characteristics of Mars'solar wind interaction compared to that of Venus may be explicable on this basis.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Geophysical Research Letters (ISSN 0094-8276); 15; 737-739
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    Gravity waves in the upper atmosphere of Venus (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The transfer function model of Mayr et al. (1984, 1987) for a dissipative multiconstituent atmosphere on earth was modified to describe gravity waves in the thermosphere of Venus in terms of spherical and Fourier harmonics. This model is used to interpret density perturbations in CO2, O, and He which were observed with the orbital neutral mass spectrometer on Pioneer Venus. Results indicate that, in agreement with observations, for localized sources in the lower atmosphere and thermosphere of the same magnitude day and night, the computed wave amplitudes at satellite altitudes are about a factor of 3 to 5 larger during the night than during the day (due to the large night to day increase in the thermospheric temperature); waves excited in the lower atmosphere propagate more obliquely, and geometric attenuation and dissipation are less important than for the thermosphere. Due to wind-induced diffusion, the computed wave amplitudes for CO2, O, and He are of comparable magnitude (with the magnitude of CO2 being the largest).
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 93; 11247-11
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    Wavelike perturbations observed in the neutral thermosphere of Venus (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Wavelike perturbations are evident in the neutral thermosphere measurements of He, N, O, N2, and CO2 by the Pioneer Venus orbiter neutral mass spectrometer. In the wavelength range from 100 to 600 km, the amplitudes of the various species are comparable in magnitude, with CO2 having the largest amplitude, and with helium out of phase with respect to the heavier species. On the dayside, the small-scale variations of CO2 and N2 increase with increasing altitude from 170 to 210 km, with CO2 having the largest slope. Simple and complex wave structures are observed, including wave trains and pulselike events. There is more activity during nighttime than during daytime, and larger values of the activity occur in the vicinity of the predawn and postdusk terminator sectors. Below 160 km, the standard deviation of the CO2 density on the nightside is 12 percent, about 3 times the daytime value. The data are consistent with the interpretation that the density perturbation are due to gravity waves propagating upward from the lower thermosphere.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 93; 11237-11
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    The distribution and significance of evaporitic weathering products on Antarctic meteorites (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: This paper examines the occurrence of white evaporitic deposits on Antarctic meteorites from the U.S. collection, as a function of meteorite compositional group and weathering category. Evaporites occur with unusual frequency on carbonaceous chondrites. Almost two-thirds of all evaporite-bearing meteorites belong to weathering categories A, A/B, and B. Where chemical data were available, surficial evaporite deposits could be associated with elemental anomalies in meteorite interiors.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Meteoritics (ISSN 0026-1114); 23; 151-159
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  • 49
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    Microbeam analysis of four chondritic interplanetary dust particles for major elements, carbon and oxygen (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Chemical compositions determined using electron excited X-rays are reported for four interplanetary dust particles collected in the stratosphere. These analyses include measurements of carbon and oxygen abundances which are important elements in these primitive materials. Spot analyses show very heterogeneous compositions on a micrometer scale although average composition approaches that of C1 carbonaceous chondrites. While the spot analyses show intermediate compositions between cometary dust and carbonaceous chondrites, the heterogeneity more closely resembles that of comet Halley dust particles.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Meteoritics (ISSN 0026-1114); 23; 113-121
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    Cloud microphysics of the giant planets (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The characteristic time constants for the atmospheres of the giant planets were compared for the purpose of finding analogs for clouds in the atmospheres of these planets among the several types of cloud systems found on earth. The NH3 clouds on Jupiter and Saturn were found to be weakly precipitating systems, similar to the thicker cirrus clouds on earth, while the H2O clouds were found to be much more massive than the water clouds on earth. The CH4 and H2O clouds on Uranus and Neptune are completely unlike any cloud on earth, being 10 to 100 times more massive than the densest water clouds on earth. It is concluded that, while the microphysical characteristics of the clouds on Jupiter and Saturn are comparable to those of terrestrial stratus and cumulus clouds, the massive clouds on Uranus and Neptune reach conditions unlike anything on earth.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of the Atmospheric Sciences (ISSN 0022-4928); 45; 2066-208
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    Particle properties and the large-scale structure of planetary rings - Rebound characteristics and viscosity (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The present treatment of the apparently paradoxical reversal of momentum transport, or 'negative viscosity', in such swarms of particles on Keplerian orbits as planetary rings, illuminates the importance of particles' physical properties. Even the slightest deviation from the idealized (uniform, highly elastic, perfectly slippery, spherical) particles will affect viscosity, yielding predictions that are inconsistent with the observed ring structure. It is presently suggested that the size of the larger bodies in the rings determines random velocities, viscosity, and a substantial portion of ring structural characteristics.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 75; 527-539
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    Geologic implications of spectrophotometric measurements of Europa (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Photometric functions and reflectances have been obtained from spectrophotometric measurements of Voyager images of Europa for (1) six mapped geologic terrains, (2) three types of lineaments, and (3) the brown spots. The results thus obtained suggest that Europa's materials fall into two main categories: a comparatively clean ice that constitutes the plains, and a darker and redder, silicate-rich material that makes up the brown spots and the wedge-shaped bands. Reflectance profiles obtained across the wedge-shaped bands and triple bands indicate similar albedo and color changes, implying similar structures for both of these features.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 75; 437-449
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    Voyager 2 imaging eclipse observations of the Jovian high altitude haze (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: High stratospheric haze layer characteristics are presently explored in view of Voyager 2 wide-angle camera images of the Jupiter northern hemisphere dawn and dusk limbs. It is noted that such phenomena as particle size, refractive index, haze top altitude, and density have major effects on the intensity of scattered light; a unique solution specifying each of these is not possible. Important limits on the altitude of the haze top and haze extinction coefficients in the high stratosphere are nevertheless derived. The images show considerable, unanticipated differences between the dawn and dusk limbs at high latitude, suggesting a dynamically active upper atmosphere.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 75; 381-398
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  • 54
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    Infrared processes in the Jovian auroral zone (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: In the present theoretical model of the Jovian auroral zone's CH4 and H2 vibrational excitation and deexitation processes, the calculation of the emission intensities of nu3 and nu4 bands of CH3 assume that electrons are the bombarding particles. The most uncertain part of the model calculation involves the energy flux spectrum of incident electrons on the auroral zone. Comparisons with Voyager 1 IRIS observations indicate a domination of the nonthermal, directly or indirectly particle bombardment-derived emission by the thermal emission of the CH4 band.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 75; 399-408
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  • 55
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    Solid-state ice volcanism on the satellites of Uranus (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Voyager images of the Uranian satellites Ariel and Miranda show flow features with morphologies indicating that ice has been extruded to the satellites' surfaces in the solid state. These images provide the first observational evidence for solid-state ice volcanism in the solar system. Topographic profiles have been measured across a number of flow features on Ariel. With a simple model of extrusion, spreading, and cooling of a viscous flow, the initial viscosity of the flow material is found to have been no more than about 10 to the 16th poise, far lower than expected for H2O ice at the ambient surface temperatures in the Uranian system. Sharply reduced viscosities may have resulted from incorporation of ices like NH3 or CH4 in the Uranian satellites.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Science (ISSN 0036-8075); 241; 1322-132
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  • 56
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    Physical properties of the planet Mercury (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The global physical properties of Mercury are summarized with attention given to its figure and orbital parameters. The combination of properties suggests that Mercury has an extensive iron-rich core, possibly with a still-functioning dynamo, which is 42 percent of the interior by volume. Mercury's three major axes are comparable in size, indicating that the planet is a triaxial ellipsoid rather than an oblate spheroid. In terms of the domination of its surface by an intermediate plains terrane, it is more Venus- or Mars-like; however, due to the presence of a large metallic magnetic core, its interior may be more earth-like.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
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  • 57
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    Tharsis block tectonics on Mars (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The concept of block tectonics provides a framework for understanding many aspects of Tharsis and adjoining structures. This Tharsis block tectonics on Mars is manifested partly by mantle-related doming and partly by response to loading by subsequent volcanic construction. Although the origin of the volcanism from beneath Tharsis is a subject of controversy explanations have to include inhomogeneities in Martian internal structure, energy distribution, magma accumulation and motion below the lithosphere. Thermal convection can be seen as a necessary consequence for transient initial phase of Martian cooling. This produced part of the elevated topography with tensional stresses and graben systems radial to the main bulge. The linear grabens, radial to the Tharsis center, can be interpreted to indicate rift zones that define the crustal block boundaries. The load-induced stresses may then have contributed on further graben and ridge formation over an extended period of time.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Earth, Moon, and Planets (ISSN 0167-9295); 41; 201-216
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  • 58
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    Accretional heating of the satellites of Saturn and Uranus (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: A model developed specifically for accretional heating of small icy satellites of massive planets was used to investigate the effects of various parameters on the accretional heating of the Saturn and Uranus satellites. It was shown that accretional heating is completely dominated by cisplanetary impactors, with substantial deposition of heat occurring well below a satellite's surface. Three parameters that have large uncertainties were found to affect accretional temperature profile: the Safronov parameter for cisplanetary impactors, the fraction of impactor energy deposited below the surface, and the exponent in the impactor size-distribution equation. For most satellites, the depth of maximum heating and the maximum temperature reached have smooth positive dependences on satellite size. Accretional heating of these satellites is insufficient to melt H2O ice, but, if NH3 or CH4 are present, accretional heating may produce a warm buoyant mobile zone tens of kilometers below the surface.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 93; 8779-879
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  • 59
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    Geological observation of impact craters on Mars and the earth using remote-sensing methods (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: It has been suggested that future multispectral and radar remote sensing of Martian craters can be developed on the basis of studies of multispectral and radar signatures of earth craters which are reasonable analogues of the Martian varieties. The present paper is a contribution toward establishing a methodology for detecting the record of very fresh craters on Mars.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Astronomicheskii Vestnik (ISSN 0320-930X); 22; 213-228
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  • 60
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    Measured line positions and strengths of methane between 5500 and 6180/cm (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Calculations for the positions and strengths of over 2000 methane absorption lines stronger than 0.0001/sq cm per atm have been obtained in the 5500-6180/cm spectral region. Spectra were obtained at room temperature using the Fourier transform spectrometer at the Kitt Peak National Observatory solar telescope. The 2nu3 band strength of C-12H4 was shown to be 1.641/sq cm per atm. A Herman-Wallis-type correction of 1 + 0.0298 m + 0.000536 sq m was also found.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Applied Optics (ISSN 0003-6935); 27; 4038-405
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  • 61
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    Discovery of sodium and potassium vapor in the atmosphere of the moon (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: A ground-based telescopic study of the lunar surface with high resolution spectroscopy has led to the discovery of sodium and potassium vapor 'atmospheres'. The scale height for the sodium atmosphere is 120 + or - 42 km, and for potassium 90 + or - 20 km; these values imply that the effective temperature of the two elements closely approximates that of the lunar surface. The sodium density at the south polar region is similar to that at the subsolar point, indicating widespread distribution of the vapor. The ratio of sodium to potassium densities, at 6 (+ or - 3):1, is close to the lunar surface ratio and suggests that the atmosphere originated in the vaporization of surface minerals.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Science (ISSN 0036-8075); 241; 675-680
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  • 62
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    High temperatures in the early solar nebula (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: One fundamental controversy about terrestrial planet and asteroid formation is the discrepancy between meteoritical evidence for high temperatures (1500 to 2000 K) in the inner solar nebula, and much lower theoretical temperature predictions on the basis of models of viscous accretion disks that neglect compressional heating of infalling gas. It is shown here that rigorous numerical calculations of the collapse of a rotating, three-dimensional presolar nebula are capable of producing temperatures on the order of 1500 K in the asteroid region (2.5 astronomical units), in either nearly axisymmetric or strongly nonaxisymmetric nebula models. The latter models may permit significant thermal cycling of solid components in the early inner solar nebula.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Science (ISSN 0036-8075); 241; 565-567
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  • 63
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    Solar system history as recorded in the Saturnian ring structure (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Holberg's analysis of the Voyager Saturn photographs in reflected and transparent light, and occultation data of stars seen through the rings are discussed. A hyperfine structure with 10,000 ringlets can be explained by the Baxter-Thompson negative diffusion. This gives the ringlets a stability which makes it possible to interpret them as fossils which originated at cosmogonic times. It is shown that the bulk structure can be explained by the combined cosmogonic shadows of the satellites Mimas and Janus and the Shepherd satellites. This structure originated at the transition from the plasma phase to the planetesimal phase. The shadows are not simple void regions but exhibit a characteristic signature. Parts of the fine structure, explained by Holberg as resonances with satellites, are interpreted as cosmogonic shadow effects. However, there are a number of ringlets which can neither be explained by cosmogonic nor by resonance effects. Analysis of ring data can reconstruct the plasma-planetesimal transition with an accuracy of a few percent. Previously announced in STAR as N84-12013
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Astrophysics and Space Science (ISSN 0004-640X); 97; 1, No; 79-94
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  • 64
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    Stability of streams and lakes on Mars (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The freezing of small Martian streams is modelled for a variety of climatic conditions, on the supposition that the Martian atmosphere may have been considerably thicker in the past, at the time of the formation of the valley networks. This model examines the energy balance at the upper and lower surfaces of ice on streams, in order to determine the rate at which ice thickens with time. Results indicate that freezing rates are not strongly dependent on atmospheric pressure, and, under windy conditions, dependence on atmospheric pressure is even weaker. It is noted that the main problem in valley formation is in initiating the flow. Groundwater seepage alone is inadequate, due to the difficulty of groundwater system replenishment.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 56; 476-495
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  • 65
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    Implications of the GSFC Q3 model for trapped particle motion (1988)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The Uranus magnetic field model of Connerney et al. (1987), designated GSFC Q3, is used to compute field geometric invariant parameters that determine the adiabatic motion of energetic charged particles trapped in the Uranian magnetosphere, performing computations only for points located along the Voyager 2 flyby trajectory. The L-shell values computed along the Voyager-2 trajectory were compared with L shell values corresponding to the orbital positions for the Uranian satellites Ariel, Umbriel, Miranda, and Titania for a time period centered on the time of the Voyager 2 closest approach to the planet. Bimodal distributions of L minima asociated with the orbital motion of the moons are obtained, thus complicating the model predictions and correlations with charged particle data. The location of charged particle absorption signatures associated with the sweeping effects of the Uranian satellites is reasonably predicted, but significant discrepancies remain which cannot be explained by Q3 model uncertainties.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 93; 5505-551
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  • 66
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    Large amplitude MHD waves upstream of the Jovian bow shock (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Observations of large amplitude MHD waves upstream of Jupiter's bow shock are analyzed. The waves are found to be right circularly polarized in the solar wind frame, which suggests that they are propagating in the fast magnetosonic mode. A complete spectral and minimum variance eigenvalue analysis of the data was performed. The power spectrum of the magnetic fluctuations contains several peaks. The fluctuations at 2.3 MHz have a direction of minimum variance anti-parallel to the direction of the average magnetic field. Several harmonics at 6, 9, and 12 MHz are also present. The direction of minimum variance of these fluctuations lies at approximately 40 deg to the magnetic field. It is argued that these fluctuations are waves excited by protons reflected off the Jovian bow shock. The inferred speed of the reflected protons is about two times the solar wind speed in the solar wind frame. A linear instability analysis is presented that suggests an explanation for many of the observed features of the observations. The fluctuations apparently contain a significant fraction of magnetic energy that is linearly polarized and in the Alfven mode.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 88; 9989-999
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    Light element geochemistry and spallogenesis in lunar rocks (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Abundance and isotopic compositions are measured for the very volatile elements carbon, nitrogen and sulfur in 11 lunar rocks representing a wide spectrum of textures and compositions. Samples were combusted sequentially at three temperatures in order to remove terrestrial contaminants before melting the lunar rock and liberating lunar volatiles. The combustion results indicate very little terrestrial sulfur contamination, with sulfur contents correlated with the TiO2 contents of the basalts analyzed. Sulfur isotopic compositions are remarkably uniform and similar to the Canon Diablo meteorite standard. Nitrogen levels are found to be no greater than those obtained with procedural blanks, corresponding to abundances less than 0.1 microg/g. Stable nitrogen isotope measurements indicate a spallogenic N-15 production rate of 4.1 x 10 to the -6th microg N-15/g sample/million years, in agreement with previous estimates. No indigenous carbon in excess of procedural blank levels of about 0.7 microg/g is found in lunar basalts. Levels of 1 to 5 microg/g found in highland rocks may derive from meteoritic or terrestrial sources. The average measured spallogenic C-13 production rate is 4.1 x 10 to the -6th microg C-13/g sample/million years.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 47; 1769-178
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  • 68
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    The flux and source of energetic protons in Saturn's inner magnetosphere (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The flux of energetic protons in Saturn's inner magnetosphere was observed in two channels from 48 to 63 and 63 to 160 MeV. Absorption features due to the G ring and the satellites Enceladus and Mimas were easily identifiable. The flux observed in the absorption slot of Mimas can be maintained by the decay of a cosmic ray albedo neutron flux of 0.007/sq cm/s/sr. This flux is entirely consistent with calculations of the neutron flux produced by galactic cosmic ray interactions with the rings of Saturn. The omnidirectional proton flux of 0.0082/sq cm/s at 2.734 R sub s requires a residence time of 30 years. Both the residence time and the energy spectrum are comparable to those found in the inner radiation belt of the Earth. The angular distribution is nearly isotropic in the Mimas slot and beyond 4R sub s. Otherwise the pitch angle distribution is pancake and is approximated by sin(n)theta with n in the range 2 to 7. This distribution is consistent with an isotropic neutron source in the ring plane. Previously announced in STAR as N83-22084
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 88; 8923-893
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  • 69
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    Survey of low-energy plasma electrons in Saturn's magnetosphere - Voyagers 1 and 2 (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The low energy plasma electron environment within Saturn's magnetosphere was surveyed by the Plasma Science Experiment (PLS) during the Voyager encounters with Saturn. Over the full energy range of the PLS instrument (10 eV to 6 keV) the electron distribution functions are clearly non-Maxwellian in character; they are composed of a cold (thermal) component with Maxwellian shape and a hot (suprathermal) non-Maxwellian component. A large scale positive radial gradient in electron temperature is observed, increasing from less than 1 eV in the inner magnetosphere to as high as 800 eV in the outer magnetosphere. Three fundamentally different plasma regimes were identified from the measurements: (1) the hot outer magnetosphere, (2) the extended plasma sheet, and (3) the inner plasma torus. Previously announced in STAR as N83-34872
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 88; 8847-887
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    The Z3 zonal harmonic model of Saturn's magnetic field Analyses and implications (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The planetary magnetic field of Saturn has been studied by the spacecraft Pioneer 11 in 1979, Voyager 1 in 1980, and Voyager 2 in 1981. The field is found to be primarily dipolar and axially coincident with the rotation axis, but with significant quadrupole and octupole moments. The harmonic terms are g1(0) = 21535 nT, g2(0) = 1642 nT, and g3(0) = 2743 nT. This model field, Z3, in conjunction with a model for an equatorial ring current, represents very precisely the in situ magnetic-field measurements and data on charged-particle absorption by satellites and rings within 8 Saturn radii of the planet. However, this axisymmetric model fails to explain the periodic modulation of Saturn's kilometric radiation or Saturn's electrostatic discharges. This enigma of Saturn's magnetosphere remains unsolved in spite of extensive reconsideration of all available data bearing on this issue.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 88; 8771-877
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    Photometry and polarimetry of Saturn at 2640 and 7500 A (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Voyager 2 photometric and polarimetric data are reduced and tabulated, with spatially resolved limb-to-terminator scans across Saturn's equatorial zone providing information on the altitude distribution of UV-absorbing hazes, together with the phase function and polarizing properties of stratospheric and tropospheric aerosols. It is found that the UV photometry and polarimetry are best fit by Rayleigh's phase matrix. A stratospheric haze of small particles is allowed as long as the optical depth is near unity or less, and the center of the haze layer is in the 30 to 70 mbar region. The altitudes presently derived for three latitudes agree with those obtained by ground-based methane band studies and analyses from Pioneer 11. A high altitude absorber is abundant in the polar regions.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 88; 8679-869
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    Morphology and chemistry of projectile residue in small experimental impact craters (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Small-scale impact craters (5-7 mm in diameter) were produced with a light gas gun in high purity Au and Cu targets using soda lime glass (SL) and man-made basalt glass (BG) as projectiles. Maximum impact velocity was 6.4 km/s resulting in peak pressures of approximately 120-150 GPa. Copious amounts of projectile melts are preserved as thin glass liners draping the entire crater cavity; some of this liner may be lost by spallation, however. SEM investigations reveal complex surface textures including multistage flow phenomena and distinct temporal deposition sequences of small droplets. Inasmuch as some of the melts were generated at peak pressures greater than 120 GPa, these glasses represent the most severely shocked silicates recovered from laboratory experiments to date. Major element analyses reveal partial loss of alkalis; Na2O loss of 10-15 percent is observed, while K2O loss may be as high as 30-50 percent. Although the observed volatile loss in these projectile melts is significant, it still remains uncertain whether target melts produced on planetary surfaces are severely fractionated by selective volatilization processes.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research, Supplement (ISSN 0148-0227); 88; B353-B36
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    The production curve for agglutinates in planetary regoliths (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Models for the production of agglutinates are developed that can be applied to the lunar surface or to any planetary or asteroidal body lacking an atmosphere. Models are developed using rate equations for progressively more complex situations and range from Model 1, which is a simple linear increase of agglutinate content with time, to Model 4, which includes provision for recycling of existing agglutinates and replenishment and burial of exposed soil. Model 4 has some aspects of a steady state because, depending on the rate constants, agglutinate content may be limited to an intermediate value, even for long exposure times. In an extreme case, agglutinate content may be limited to a value near zero. These models predict that agglutinates should be low in abundance in areas of thin regolith, such as the Lunokhod-2 site on the moon, and on asteroids. The models may also help explain the apparent low agglutinate abundances of lunar regolith breccias and meteorite regolith breccias.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research, Supplement (ISSN 0148-0227); 88; B193-B19
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    Ancient crustal components in the Fra Mauro breccias (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Texturally pristine clasts preserve primary petrographic relationships and mineral compositions, yielding insights into igneous processes of the early lunar crust that cannot be gained from highly shocked and brecciated 'chemically pristine' samples. The use of texture as a prime criterion allows for expansion of the data base derived solely from chemical criteria, and provides complementary data. Texturally pristine clasts from the Apollo 14 site studied here include anorthosite, troctolites, gabbronorites, and basalts. Alkali anorthosites are plagioclase orthocumulates and may form by flotation in Mg-suite plutons. Ferroan anorthosite was cataclastically deformed and metamorphosed to granulite facies. Troctolites include both 01 + Plg and 01 + En + Plg cumulates. Major and trace element analyses of two troctolites reveal 'eastern' geochemical affinities that contrast other 'western' troctolites. Gabbronorites are Pig + Plg + or - Sp cumulates whose parent magmas may range from high-Al to intermediate-Ti mare basalt. At least three varieties of mare basalt are found at Apollo 14: high-Al, low-Ti; low-Al, intermediate-Ti; and low-Al, Ti VHK basalt. VHK (Very High Potassium) basalt is a new variety indigenous to Apollo 14.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research, Supplement (ISSN 0148-0227); 88; B177-B19
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    An upper bound on the radius of a highly electrically conducting lunar core (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Parker's (1980) nonlinear inverse theory for the electromagnetic sounding problem is converted to a form suitable for analysis of lunar day-side transfer function data by: (1) transforming the solution in plane geometry to that in spherical geometry; and (2) transforming the theoretical lunar transfer function in the dipole limit to an apparent resistivity function. The theory is applied to the revised lunar transfer function data set of Hood et al. (1982), which extends in frequency from 10 to the -5th to 10 to the -3rd Hz. On the assumption that an iron-rich lunar core, whether molten or solid, can be represented by a perfect conductor at the minimum sampled frequency, an upper bound of 435 km on the maximum radius of such a core is calculated. This bound is somewhat larger than values of 360-375 km previously estimated from the same data set via forward model calculations because the prior work did not consider all possible mantle conductivity functions.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research, Supplement (ISSN 0148-0227); 88; B97-B102
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    Atmospheric tides on Venus. III - The planetary boundary layer (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Diurnal solar heating of Venus' surface produces variable temperatures, winds, and pressure gradients within a shallow layer at the bottom of the atmosphere. The corresponding asymmetric mass distribution experiences a tidal torque tending to maintain Venus' slow retrograde rotation. It is shown that including viscosity in the boundary layer does not materially affect the balance of torques. On the other hand, friction between the air and ground can reduce the predicted wind speeds from about 5 to about 1 m/sec in the lower atmosphere, more consistent with the observations from Venus landers and descent probes. Implications for aeolian activity on Venus' surface and for future missions are discussed.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus (ISSN 0019-1035); 56; 165-175
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  • 77
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    Structure and dynamics of Saturn's outer magnetosphere and boundary regions (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: In 1979-1981, the three USA spacecraft Pioneer 11 and Voyagers 1 and 2 discovered and explored the magnetosphere of Saturn to the limited extent possible on flyby trajectories. Considerable variation in the locations of the bow shock (BS) and magnetopause (MP) surfaces were observed in association with variable solar wind conditions and, during the Voyager 2 encounter, possible immersion in Jupiter's distant magnetic tail. The limited number of BS and MP crossings were concentrated near the subsolar region and the dawn terminator, and that fact, together with the temporal variability, makes it difficult to assess the three dimensional shape of the sunward magnetospheric boundary. The combined BS and MP crossing positions from the three spacecraft yield an average BS-to-MP stagnation point distance ratio of 1.29 +/- 0.10. This is near the 1.33 value for the Earth's magnetosphere, implying a similar sunward shape at Saturn. Study of the structure and dynamical behavior of the outer magnetosphere, both in the sunward hemisphere and the magnetotail region using combined plasma and magnetic field data, suggest that Saturn's magnetosphere is more similar to that of Earth than that of Jupiter. Previously announced in STAR as N83-30346
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 88; 8791-880
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  • 78
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    Channels and valleys on Mars (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Tentative conclusions about the origins of channels and valleys on Mars based on the consensus of investigators who have studied the problem are presented. The morphology of outflow channels is described in detail, and the morphology, distribution, and genesis of Martian valleys are addressed. Secondary modification of channels and valleys by mass-wasting phenomena, eolian processes, cratering, and mantling by lava flows is discussed. The physics of the flows needed to account for the immense volumes of Martian outflow channels is considered in detail, including the possible influence of debris flows and mudflows, glaciers, and ice sheets. It is concluded that Mars once probably possessed an atmosphere with higher temperatures and pressures than at present which played an essential role in an active hydrological cycle.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Geological Society of America, Bulletin (ISSN 0016-7606); 94; 1035-105
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  • 79
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    Three Mars years - Viking Lander 1 imaging observations (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The Mutch Memorial Station (Viking Lander 1) on Mars acquired imaging and meteorological data over a period of 2245 martian days (3.3 martian years). This article discusses the deposition and erosion of thin deposits (ten to hundreds of micrometers) of bright red dust associated with global dust storms, and the removal of centimeter amounts of material in selected areas during a dust storm late in the third winter. Atmospheric pressure data acquired during the period of intense erosion imply that baroclinic disturbances and strong diurnal solar tidal heating combined to produce strong winds. Erosion occurred principally in areas where soil cohesion was reduced by earlier surface sampler activities. Except for redistribution of thin layers of materials, the surface appears to be remarkably stable, perhaps because of cohension of the undisturbed surface material.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Science (ISSN 0036-8075); 222; 463-468
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  • 80
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    Stability and capture of asteroids (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The problem of stability of asteroids is treated from the point of view of Hill's stability-concept and using Lyapunov's Characteristic Numbers. The quantitative measure of stability (S) introduced earlier is evaluated for over 300 asteroids and a surprisingly simple relation is established between the semi-major axes of some of the asteroids' orbits and S. A detailed analysis is presented of the Lyapunov Characteristic Numbers for two minor planets and the time-variation of these numbers is discussed. The technology of capture of asteroids is vitally dependent on their orbital stability, therefore, these two problems, i.e., capture and stability, are closely related. In fact, some predictable instabilities may be properly utilized to capture and/or change asteroidal orbits to accomplish collisions with the Earth.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Sao Paulo Univ. The Motion of Planets and Nat. and Artificial Satellites, Volume 2; p 39-46
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  • 81
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    A Sr and Nd isotopic study of five Yamato polymict eucrites and a comparison to other Antarctic and ordinary eucrites (1983)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Sr and Nd isotopic analysis of five Yamato polymict eucrites indicate that these samples formed at about 4.6 Ga ago with initial Sr and Nd ratios essentially the same as the analyzed non-Antarctic eucrites. The Yamato eucrites have Sr, Sm, and Nd concentrations that consistently lie among the highest found in eucritic samples. This characteristic identifies these Yamato samples as a closely related group. Comparisons between these Yamato samples and other Antarctic polymict eucrites clearly estabishes that they all share some characteristic trace element features. Comparisons of Antarctic polymict eucrites with non-Antarctic ordinary eucrites reveal consistent differences. The most obvious is an enrichment of Rb in the polymict eucrites. These comparisons suggest that the Antarctic polymict eucrites belong to a single large family of material that is itself fairly diverse and distinct from the non-Antarctic eucrites.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: National Institute of Polar Research, Memoirs, Special Issue (ISSN 0386-0744); 30, D
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  • 82
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    Condensation of chondrules (1983)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Analysis of current experimental results concerned with the kinetic constraints on chondrule formation showed that the major physical properties of chondrules could have been produced by direct condensation of metastable liquid silicates droplets from a hot gas in the primordial nebula. It is argued that such a condensation process would have to be followed by crystallization, accretion, and partial comminution of the droplets. The chemical mechanisms driving this process are described, including: nucleation constraints on comminution and crystallization; slow transformations and chemical reactions in chain silicates; and the slow diffusion of ions. It is shown that the physical mechanisms for chondrule condensation are applicable to a broad spectrum of chondrule sources.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
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  • 83
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    External control of planetary radio emission (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Recent studies using data from Voyagers 1 and 2 to correlate variations in the Saturn kilometric radiation (SKR) with changes in solar-wind properties are summarized and illustrated with graphs. Best SKR correlations have been obtained with the solar-wind ram pressure and the related kinetic energy flux. It is pointed out that the related phenomenon on earth, the auroral kilometric radiation, occurs mainly in the nightside auroral region (as opposed to the dayside cleft region for SKR) and is best correlated with solar-wind velocity and inverted-V electron-precipitation events, implying a different stimulation process. The evidence for solar-wind control of the non-Io-related decametric radiation of Jupiter is also reviewed.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Oesterreichische Akademie der Wissenschaften, mathematisch-naturwissenschaftliche Klasse, Sitzungsberichte, Abteilung 2 (ISSN 0723-9319); 192; 8-10,
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  • 84
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    Saturn - Origin and composition of its inner moons and rings (1980)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Theoretical modelling of the contraction of the primitive protosaturnian cloud, using ideas of supersonic turbulent convection, suggests that each of Saturn's inner moons, excepting Rhea, condensed above the ice-point of water and consists primarily of hydrous magnesium silicates. It is predicted that Voyager 1 may find that the satellite mean densities steadily increase towards the planet and that the rocky moons are irregular in shape.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Physics Letters; 80A; Nov. 24
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  • 85
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    Gravity anomalies on Venus (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Doppler radio tracking of the Pioneer Venus orbiter has provided gravity measures over a significant portion of Venus. Feature resolution is approximately 300-1000 km within an area extending from 10 deg S to 40 deg N latitude and from 70 deg W to 130 deg E longitude (approximately equal to 200 deg). Many anomalies were detected, and there is considerable correlation with radar altimetry topography (Pettengill et al., 1980). The amplitudes of the anomalies are relatively mild and similar to those on earth at this resolution. Calculations for isostatic adjustment reveal that significant compensation has occurred.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research; 85; Dec. 198
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  • 86
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    Distribution and source of the UV absorption in Venus' atmosphere (1980)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The model predictions were compared with the Pioneer Venus probes and orbiter to determine the composition of the UV absorbing materials. The simulations were carried out with radiative transfer codes which included spacecraft constraints on the aerosol and gas characteristics in the Venus atmosphere; gaseous SO2 (a source of opacity at the wavelengths below 0.32 microns), and a second absorber (which dominates above 0.32 microns) were required. The UV contrast variations are due to the optical depth changes in the upper haze layer producing brightness variations between equatorial and polar areas, and to differences in the depth over which the second UV absorber is depleted in the highest portion of the main clouds.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research; 85; Dec. 30
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  • 87
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    Measurements of thermal structure and thermal contrasts in the atmosphere of Venus and related dynamical observations - Results from the four Pioneer Venus probes (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The thermal structure of the Venus atmosphere and differences in structure with latitude (up to 60 deg) and clock hour (from midnight to 8 AM) have been measured in situ from a height of 126 km to the surface by instruments on the four Pioneer Venus entry probes. It is found that thermal contrasts below 45 km are a few K, with the midlatitudes warmer than both equatorial and high latitudes. Considerable temperature and pressure differences with latitude develop in the clouds (25 K and 20 mbar level). In addition, upward of 110 km, there is evidence of large-amplitude temperature oscillations with altitude, believed to signify the presence of large-amplitude waves, perhaps thermal tides. Agreement of structure data from other Pioneer Venus experiments is generally excellent.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research; 85; Dec. 30
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  • 88
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    Dust in Jupiter's magnetosphere. I - Physical processes. II - Origin of the ring. III - Time variations. IV - Effect on magnetospheric electrons and ions (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The physical processes acting on charged microscopic dust grains in the Jovian atmosphere involve electromagnetic forces which dominate dust particle dynamics and diffusion across field lines resulting from random charge fluctuations of the dust grains. A model of the Jovian ring hypothesizes that the 'visible' ring particles are produced by erosive collisions between an assumed population of kilometer-sized parent bodies and submicron-sized magnetospheric dust particles. Fluctuations in the ring topology and intensity are determined over various time scales, showing that the ring is a quasipermanent and quasistable characteristic of the Jovian system. Finally, the interaction of the Jovian energetic belt electrons and the Jovian plasma with an ambient dust population is examined; the distribution of dust ejected from Io in the inner magnetosphere and losses of magnetospheric ions and electrons due to direct collisions with charged dust particles are calculated.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Planetary and Space Science; 28; Dec. 198
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  • 89
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    Io control of Jovian radio emission (1980)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The possibility of Io controlling Jovian decametric radio emission, particularly in the region below 22 MHz, is discussed. Results of a two-year survey at 26.3 at 26.3 MHz are presented which demonstrate the control of Io over a high-intensity storm component of the radio emission and the independence of a weak radio component from the phase of Io, as was observed at lower frequencies. It is thus hypothesized that Io control is a flux-dependent rather than a frequency-dependent phenomenon, and results of analyses at 18 and 10 MHz which support this hypothesis are presented. The apparent correlation between frequency and Io control is thus shown to result from a selection effect due to the increase of non-Io emission with decreasing frequency and relative antenna detection threshold. This result implies a contiguous Io-controlled source region extending out several Jovian radii along the Io flux tube.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Nature; 287; Oct. 30
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  • 90
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    Viscous flow and crystallization behavior of tektite glasses (1980)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The variation of viscosity with temperature was determined in the 200-2000 K range for a Muong Nong tektite material. The viscosity at the liquidus temperature of 1320 C is 20,000 P; treatments between 900 and 1300 C do not result in significant crystallization in the natural sample except when the sample is heated in contact with a synthetic tektite composition. Two synthetic microtektite with lower SiO2 contents than the Muong Nong material were also examined; heat flow calculations were performed for 2.5 to 10 cm spheres of tektite when cooling by radiation.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research; 85; Oct. 10
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  • 91
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    The occurrence rate, polarization character, and intensity of broadband Jovian kilometric radiation (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The paper describes the major observational features of one new component of Jupiter's radio emission spectrum, the broadband kilometer wavelength radiation, or bKOM. This study, using the Voyager Planetary Radio Astronomy (PRA) experiments, reveals that the overall occurrence morphology, dynamic spectra, and polarization character of bKOM are strong functions of the latitude and/or local time geometry of the observations. The postencounter data show a decline in the mean occurrence rates and power level of bKOM and, in particular, a depletion in the occurrence rate at those same longitudes where the detection rate is a maximum before encounter. Additionally, the polarization sense undergoes a permanent reversal in sign after encounter, whereas the time-averaged wave axial ratio and degree of polarization remain relatively unchanged. Finally, no evidence of any control by Io is found. The strong dependence of the morphology on local time suggests a source whose beam is nearly fixed relative to the Jupiter-sun line
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research; 85; Aug. 1
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  • 92
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    The case against UV photostimulated oxidation of magnetite (1980)
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    Publikationsdatum: 2011-08-17
    Beschreibung: The kinetics of magnetite oxidation in O2-bearing atmospheres in the presence of electromagnetic radiation was studied. No perceptible oxidation of magnetite by ultraviolet (UV) photostimulation occurred. These results do not corroborate previous conclusions by Huguenin (1973, 1974) as to the occurrence of this process. Therefore, although the possibility that the process actually occurs cannot be ruled out, it is concluded that there is not yet a basis in laboratory experiments for inferring that UV photostimulated oxidation of magnetite occurs naturally on the surface of Mars.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Geophysical Research Letters; 7; Aug. 198
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  • 93
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    Voyager detection of nonthermal radio emission from Saturn (1980)
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    Publikationsdatum: 2011-08-17
    Beschreibung: The planetary radio astronomy experiment on board the Voyager spacecraft has detected bursts of nonthermal radio noise from Saturn occurring near 200 kilohertz, with a peak flux density comparable to higher frequency Jovian emissions. The radiation is right-hand polarized and is most likely emitted in the extraordinary magnetoionic mode from Saturn's northern hemisphere. Modulation that is consistent with a planetary rotation period of 10 hours 39.9 minutes is apparent in the data.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Science; 209; Sept. 12
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  • 94
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    Investigation of numerical properties of Hovenier's exit function equation for multiple scattering of light (1980)
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    Publikationsdatum: 2011-08-17
    Beschreibung: A technique of deriving Hovenier's exit function equation (1978) for multiple scattering, starting with a set of invariant imbedding equations, is presented. The feasibility of the exit function equation as a means to obtain reflection and transmission functions is investigated for isotropic, Rayleigh, and Henyey-Greenstein phase functions with emphasis on the numerical stability, accuracy and timing. It is possible to compute the reflection function rather accurately with an efficiency comparable to that of the standard doubling technique for the same phase functions with moderate anisotropy. The resulting transmission is slightly less accurate than the reflection function, but it may be acceptable for practical purposes.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Astrophysics and Space Science; 69; 1, Ma; May 1980
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  • 95
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    Instability of equatorial protons in Jupiter's mid-magnetosphere (1980)
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    Publikationsdatum: 2011-08-17
    Beschreibung: Two different models for the distribution function are fit to the Jovian protons seen by Pioneer 10 inbound. The models reproduce the observed energy and angular distributions. These models are then used to assess the collisionless mirror instability. Because of the pancake proton angular distributions in the equatorial ring current region, the ring current particle population appears to be mirror unstable at times, with instability growth rates of about 10 min. Such a time is consistent with observed proton flux autocorrelation times. An instability such as this (there are other candidates) may be responsible for the previously established proton flux flowing parallel to the magnetic field away from the equatorial region.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research; 85; Jan. 1
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  • 96
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    Saturn's rings - Particle composition and size distribution as constrained by observations at microwave wavelengths. II - Radio interferometric observations (1980)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Theoretical models are presented of the brightness of Saturn's rings at microwave wavelengths (0.34-21.0 cm) including both intrinsic ring emission and diffuse scattering by the rings of the planetary emission. In addition, several previously existing sets of interferometric observations of the Saturn system at 0.83, 3.71, 6.0, 11.1, and 21.0 cm wavelengths are analyzed. A comparison of models and experimental data make it possible to establish improved constraints on the properties of the rings. In particular, it is found that (1) the maximum optical depths in the rings is 1.5 + or - 0.3 referred to visible wavelengths; (2) a significant decrease in ring optical depths from 3.7 to 21.0 cm makes it possible to rule out the possibility that more than 30% of the cross section of the rings is composed of particles larger than about a meter; and (3) the ring particles cannot be primarily of silicate composition (independently of particle size), and the particles cannot be primarily smaller than about 0.1 cm, independently of composition.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus; 44; Dec. 198
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  • 97
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    Greenhouse models of Venus' high surface temperature, as constrained by Pioneer Venus measurements (1980)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Recent measurements conducted from the Pioneer Venus probes and orbiter have provided a significantly improved definition of the solar net flux profile, the gaseous composition, temperature structure, and cloud properties of Venus' lower atmosphere. Using these data, we have carried out a series of one-dimensional radiative-convective equilibrium calculations to determine the viability of the greenhouse model of Venus' high surface temperature and to assess the chief contributors to the greenhouse effect. New sources of infrared opacity include the permitted transitions of SO2, CO, and HCl as well as opacity due to several pressure-induced transitions of CO2. We find that the observed surface temperature and lapse rate structure of the lower atmosphere can be reproduced quite closely with a greenhouse model that contains the water vapor abundance reported by the Venera spectrophotometer experiment. Thus the greenhouse effect can account for essentially all of Venus' high surface temperature. The prime sources of infrared opacity are, in order of importance, CO2, H2O, cloud particles, and SO2, with CO and HCl playing very minor roles.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research; 85; Dec. 30
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  • 98
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    Cloud morphology and motions from Pioneer Venus images (1980)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The horizontal and vertical cloud structures, atmospheric waves, and wind velocities at the cloud top level were determined by the Pioneer Venus photopolarimeter images in the UV from January through March 1979. The images indicate long-term evolution of cloud characteristics, the atmospheric dynamics, and rapid small changes in cloud morphology. The clouds show a globally coordinated oscillation relative to latitude circles; retrograde zonal winds of 100 m/s near the equator are determined from the tracking of small-scale cloud properties, but two hemispheres show important variations. The zonal wind velocity in the southern hemisphere is reduced toward the poles at a rate similar to solid body rotation; the midlatitude jet stream noted by Mariner 10 is not observed.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research; 85; Dec. 30
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  • 99
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    Pioneer Venus gas chromatography of the lower atmosphere of Venus (1980)
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    Publikationsdatum: 2011-08-18
    Beschreibung: A gas chromatograph mounted in the Pioneer Venus sounder probe measured the chemical composition of the atmosphere of Venus at three altitudes. Ne, N2, O2, Ar, CO, H2O, SO2, and CO2 were measured, and upper limits set for H2, COS, H2S, CH4, Kr, N2O, C2H4, C2H6, and C3H8. Simulation studies have provided indirect evidence for sulfuric acid-like droplets and support the possibility of water vapor at altitudes of 42 and 24 km. The paper discusses the implications of these results for the origin, evolution, and present state of Venus' atmosphere.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research; 85; Dec. 30
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  • 100
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    Dynamic properties of the thermosphere inferred from Pioneer Venus mass spectrometer measurements (1980)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The data obtained by the Pioneer Venus spectrometer experiments indicate that the day-night temperature contrast on Venus is associated with wind velocities of about 200 m/s which transport oxygen, helium, and hydrogen toward the night side. A mass exchange with the mesosphere commensurate with an eddy diffusion coefficient of 3 x 10 to the 7th is required to buffer the horizontal advection so as to reproduce the observed day time bulge in oxygen and the small diurnal variations in helium. The observed time response and magnitude of the day-night density variations require transport processes to be effective over time periods between five and ten days, implying a superrotation rate or prevailing winds in excess of 50 m/s at the equator. Nonlinear mass transport results in wave steepening and contributes to the amplification of the density extrema in hydrogen and helium.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research; 85; Dec. 30
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