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  • 1
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    Composition of the Cayley Formation at Apollo 16 as inferred from impact melt splashes (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Abundances of major and trace elements and magnetic properties of 50 impact melt splashes (IMSs) from the Apollo 16 landing site are analzyed to determine the composition of their meteoritic component. MgO-Sc and Ca-Sc variation diagrams and least-squares mixing models are utilized to analyze the IMS, soil, and rock data. Consideration is given to progenitor lithologies of the IMS, the number of impact events represented by the IMS, and the heterogeneity of impact melts from single events. It is observed that the IMSs are composed of either a mixture of anorthosite and low-Sc impact melt rocks or anorthositic norite. It is determined that the surface Cayley layer is composed of TiO2, MgO, Sc, and La concentrations of 0.69, and 7.1 wt pct and 10.5 and 21.2 microg/g, respectively and 0.38 and 5.9 wt pct and 6.1 and 11.8 microg/g, respectively, for the subsurface Cayley layer. The Descartes Formation composition is estimated as TiO2, MgO, Sc, and La concentrations of 0.25, and 3.5 wt pct and 7.7 and 2.2 microg/g, respectively.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; E21-E42
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  • 2
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    Apollo 16 impact-melt splashes - Petrography and major-element composition (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Petrographic and major-element analyses are applied to 50 Apollo 16 impact-melt splash (IMS) samples in order to determine their origin and assess the nature of the subregolith source. The macroscopic analyses reveal that the IMSs exhibit a glassy appearance, but the textures range from holohyaline to hyalopilitic. Schlieren-rich glasses dominate the holohyaline areas, and the crystalline areas are mainly spherulitic. It is observed that most IMSs contain feldspathic monomineralic and lithic clasts and no regolithic materials. It is detected that the chemistry of most IMSs is not like the local regolith and appears to represent varied mixtures of VHA impact-melt breccias and anorthosite; the host rocks are mainly dimict breccias. It is concluded that the Cayley Formation is a polymict deposit composed of VHA impact-melt breccias and anorthosites. Tables revealing the macroscopic characteristics of the IMSs and the major-element composition of IMSs and various host rock are presented.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; E3-E20
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  • 3
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    Small satellites (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Satellites smaller than Mimas (r = 195 km) are distinguished by irregular overall shapes and by rough limb topography. Material properties and impact cratering dominate the shaping of these objects. Long fragmentation histories can produce a variety of internal structures, but so far there is no direct evidence that any small satellite is an equilibrium ellipsoid made up of noncohesive gravitationally bound rubble. One many bodies that orbit close to their primary the tidal and rotational components of surface gravity strongly affect the directions of local g and thereby affect the redistribution of regolith by mass wasting. Downslope movement of regolith is extensive on Deimos, and is probably effective on many other small satellites. It is shown that in some cases observed patterns of downslope mass wasting cold produce useful constraints on the satellite's mean density. The diversity of features seen in the few high-resolution images of small satellites currently available suggests that these objects have undergone complex histories of cratering, fragmentation, and regolith evolution.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 4
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    Thermal emission from Saturn's rings at 380 microns (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: 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.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 574-583
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  • 5
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    High-temperature shock formation of N2 and organics on primordial Titan (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: 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.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 332; 520-522
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  • 6
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    Evidence for interstellar SiC in the Murray carbonaceous meteorite (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Silicon carbide has been identified in two separates from the Murray carbonaceous chondrite that are enriched 20,000-fold in isotopically anomalous neon and xenon. The SiC is present in the form of crystalline grains 0.1-1 micron in size. Cubic and 111-plane-twinned cubic are the most common ordered polytypes observed so far. The anomalous isotopic composition of its carbon, nitrogen, and silicon indicates a presolar origin, probably in the atmospheres of red giants. An additional silicon- and oxygen-rich phase shows large isotropic anomalies in nitrogen and silicon, also associated with a presolar origin.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 330; 728-730
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  • 7
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    Stability of polar rings around Neptune (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An analytical and numerical study of the stability of polar rings around Neptune is presented. The stability proofs are based on various methods used to study gas disks in galaxies. It is shown that stable polar rings can exist despite energy dissipation by collisions between particles. Also, four equilibrium orientations which pass nearly over the pole of Neptune are found, two of which are stable in the presence of dissipation.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 81; 132-144
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  • 8
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    Mars - Satellite and ring search from Viking (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: 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.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 76; 160-162
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  • 9
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    Methane rain on Titan (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: 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.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 75; 255-284
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  • 10
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    Production of organic compounds in plasmas - A comparison among electric sparks, laser-induced plasmas, and UV light (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: In order to ascertain the features of organic compound-production in planetary atmospheres under the effects of plasmas and shocks, various mixtures of N2, CH4, and H2 modeling the atmosphere of Titan were subjected to discrete sparks, laser-induced plasmas, and UV radiation. The experimental results obtained suggest that UV photolysis from the plasma is an important organic compound synthesis process, as confirmed by the photolysis of gas samples that were exposed to the light but not to the shock waves emitted by the sparks. The thermodynamic equilibrium theory is therefore incomplete in the absence of photolysis.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 81; 413-428
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