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  • Other Sources  (20)
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  • 1
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    Saturn's rings - A new survey (1977)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Observations of radar returns from Saturn's rings, together with radio interferometry of their absorption of radiation from the disk, combine to require an effective radius of ring particles of about 6 cm or larger. It is suggested that the ring particles may also include, in addition to the known ice constituent, a mixture of the clathrated hydrate of methane and ammonia hydrate. A two-density model for ring particles is possible in which a matrix of low density contains many nodules of higher-density ice particles; in this case, radii nearly as large as the observed ring thickness would be possible. Improved resolution in radio observations at 21 cm or, if necessary, at longer wavelengths for narrow ring openings is perhaps the most useful method for determining upper limits on the particle size.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 2
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    Structure of Saturn's rings: Optical and dynamical considerations (1974)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The photometric phase curves of Saturn's rings are considered, as well as a conflict between dynamical and photometric models of the rings. The dependence of ring brightness on angular separation of the earth and sun as viewed from Saturn is discussed. The nonlinear brightness surge is interpreted. Some quantitative calculations were carried out for bodies in and near the asteroidal belt. Predicted density profiles of the ring obtained with Mimas in an eccentric orbit and in a circular orbit are also included.
    Keywords: ASTROPHYSICS
    Type: NASA, Washington The Rings of Saturn; p 3-15
    Format: application/pdf
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  • 3
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    Study of lunar earthshine by photoelectric photometry Semiannual report, 1 Nov. 1965 - 30 Apr. 1966 (1966)
    In:  CASI
    Details
    Publication Date: 2019-05-30
    Description: Photoelectric photometer developed to measure earth albedo and lunar earthshine
    Keywords: SPACE SCIENCES
    Type: NASA-CR-76753
    Format: application/pdf
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  • 4
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    Tidal torques on infrequently colliding particle disks in binary systems and the truncation of the asteroid belt (1980)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Conditions leading to the truncation, at the 2:1 resonance, of a disk of infrequently colliding particles surrounding the primary of a binary system are studied numerically and analytically. Attention is given to the case in which the mass ratio, q, is sufficiently small (less than about 0.1) and the radius of the disk centered on the primary allowably larger, so that first-order orbit-orbit resonances between ring material and the secondary can lie within it. Collisions are found to be less frequent than q to the -2/3 power orbital periods (the period of the forced eccentricity at the 2:1 resonance), and truncation occurs and Kirkwood gaps are produced only if the particle eccentricity is less than some critical value, estimated to be of order q to the 5/9 power, or approximately 0.02 for the sun-Jupiter case having q equal to 10 to the -3rd power.
    Keywords: ASTROPHYSICS
    Type: Icarus; 42; May 1980
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  • 5
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    A possible link between the rotation of Saturn and its ring structure (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Evidence is presented that two previously unidentified, yet conspicuous gaps in Saturn's rings lie at distances corresponding to 2/3 and 4/3 of the planet's rotation period. Gaps such as these can be produced in a ring of large bodies or small uncharged particles by a nonaxisymmetric gravitational field (both of the above can be associated with the l = m = 3 harmonic), a fact that is relevant to models of planetary interiors.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 295; Jan. 14
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  • 6
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    Saturn's rings - A survey. (1973)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: In this review paper we first discuss the dimensions of major ring features and of the disk of the planet. We then summarize the observed photometric parameters, and because frozen H2O appears to be a major ring constituent, we compare the appropriate photometric properties of various forms of snow with those of the ring. We examine several ring models, noting certain characteristics that any model should supply. In our view, a physical means of accounting for the observed ring thickness of about 2 km is a prime requirement. There appears to be one model that presents no clear observational or theoretical inconsistency.
    Keywords: SPACE SCIENCES
    Type: Icarus; 18; Feb. 197
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  • 7
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    de Sitter's theory 'melts' Europa's polar cap (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: In photoelectric observations of a series of occultations of the Jovian satellite Europa by the Jovian satellite Io it was observed that increasingly larger fractions of the north polar region of the former were covered at mid-event with each successive occultation. One of the possible explanations of the observed phenomena involves the existence of a bright north polar cap for Europa. The reported investigation shows that a second explanation may be more plausible. This explanation is related to the possibility that at mid-event the projected minimum distance between the centers of the satellites was smaller than predicted by Sampson's theory.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 258; Dec. 11
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  • 8
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    Minor planets and comets in libration about the 2:1 resonance with Jupiter (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: We examine the orbits of minor planets in a search for objects librating about the 2:1 mean-motion resonance with Jupiter. Some 30 candidates are found among the Palomar-Leiden Survey and other unnumbered minor planets. Although almost all the orbits are very uncertain, there does seem to be an indication that librators of low orbital eccentricity do exist, contrary to the hypothesis by Giffen. We also tabulate data describing 12 comets that are temporarily librating about the 2:1 resonance. Finally, we present a discussion of what are apparently 'apocentric' librations. This type of libration, of which we find seven representatives among the numbered minor planets, can occur only for sufficiently small eccentricity. For such bodies, the role of Jupiter's eccentricity is vital; it is associated with a continuing alternation between apocentric libration and an oscillation of the line of apsides.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astronomical Journal; 80; Sept
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  • 9
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    The geometric oblateness of Uranus (1980)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The paper considers photographs of Uranus obtained by the Stratoscope II balloon-borne telescope in 1970. These data have been redigitized and reanalyzed, and the geometric oblateness of Uranus was determined from the isophotes near the limb using an expression in terms of the equatorial and polar radii.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal; vol. 236
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  • 10
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    On the azimuthal brightness variations of Saturn's rings (1978)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: A simple semiquantitative explanation is presented which accounts both for the presence of the azimuthal brightness variations in Saturn's ring A and for their absence in ring B. This explanation avoids any ad hoc reliance on albedo variations and/or synchronous rotation of ring particles. Instead, it requires only some degree of self-gravitation between nearby orbiting bodies. A bias in the particle distribution and corresponding photometric effects are thereby produced the latter corresponding very closely to the variations observed in ring A. Their absence in ring B is primarily a consequence of the higher optical thickness and decreasing importance of self-gravitation in that ring.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 33; Feb. 197
    Format: text
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