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At least 559 records · Page 31
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NASA NTRS1979

Planetary rings

Two models of planetary ring formation are discussed: the break-up of a large body coming nearer to the planet than the Roche limit for the particular mechanical strength of the body would allow; and condensation of the protoplanetary nebula within a suitable Roche limit without formation of a large satellite. The location of the newly discovered Uranian rings has been interpreted in terms of three-body orbital resonance with satellites. A possible relationship between the origin and characteristics of the Uranian rings and the unusual tilt of the planetary axis is also discussed. In addition, attention is given to the polarization of light characteristic of planetary rings.

Smoluchowski, R.↗
NASA NTRS1979

International Planetary Patrol observations of Saturn's rings. I - Observations and data reduction

The paper describes the reduction procedure used for observations of Saturn's rings taken with the International Planetary Patrol Network in 1977. Corrections for atmospheric smearing are determined using an assumed ring model and performed by a two-dimensional Wiener filter developed at JPL's Image Processing Laboratory. These smearing corrections are shown to be consistent with the radial profile of the rings, not just on the major axis of the ring system, but over a range of azimuthal angle.

Lumme, K.↗
NASA NTRS1980

Damping in ring seals for compressible fluids

An analysis is presented to calculate damping in ring seals for a compressible fluid. Results show that damping in tapered ring seals (optimized for stiffness) is less than that in straight bore ring seals for the same minimum clearance. Damping in ring seals can promote fractional frequency whirl and can, thus, be detrimental. Thus, tapered seals can benefit rotor and seal stability by having lower damping as well as higher stiffness. Use of incompressible results leads to large errors.

Fleming, D. P.↗
NASA NTRS1979

Direct and inverse problems in radiation of sound from discrete random sources on two coaxial rings

An analytical model consisting of two ring sources of sound is developed to study the direct radiation in terms of correlation, coherence, and phase and also to aid in solving the inverse-radiation problem of determining the noise source in terms of farfield measurements. The rings consist of discrete sources which are either monopoles or quadrupoles with Gaussian autocorrelations. Only adjacent sources, both within and between the rings, are correlated. Results show that from the farfield information one can determine when the sources are compact or noncompact with respect to the acoustic wavelength and distinguish between the types of sources. In addition, from the inverse-radiation approach one can recover the center of mass, the location and separation distance of the ring, and the respective diameters.

Maestrello, L.↗
NASA NTRS1980

Images of Jupiter's sulfur ring

Images of the ring of singly ionized sulfur encircling Jupiter, obtained on two successive nights in April 1979, show that the ring characteristics may change dramatically in about 24 hr. On the first night the ring was narrow and confined to the magnetic equator inside Io's orbit. On the second night it was confined symmetrically about the centrifugal symmetry surface and showed considerable radial structure, including a 'fan' extending to Io's orbit. Many of the differences in the ring on the two nights can be explained in terms of differences in sulfur plasma temperature.

Pilcher, C. B.↗
NASA NTRS1980

Saturn's magnetosphere, rings, and inner satellites

The discovery of the Saturn magnetosphere and its characterization by Pioneer 11 are reported, and findings on the planet's rings and satellites obtained by energetic charged particle measurements within the inner magnetosphere are presented. Bow shock crossings identified by the Pioneer plasma analyzer and magnetometer at distances of 24.1, 23.1 and 20.0 Saturn radii indicate the presence of a magnetosphere with physical dimensions and charged particle populations intermediate between those of the earth and Jupiter, with a scale more similar to that of the earth. Particle angular distributions on the inbound leg of the trajectory are consistent with a dipole magnetic field approximately perpendicular to the planet's equator, while on the outbound leg the distributions indicate the presence of an equatorial current sheet. Charged particle absorption features are detected at the orbits of Dione and Mimas, encompassing the orbits of Tethys and Enceladus, and at 2.534 and 2.343 Saturn radii indicating the presence of satellites of diameters greater than 170 km. Charged particle measurements also confirm the Pioneer division in the rings between 2.292 and 2.336 Saturn radii, a suspected satellite at 2.82 Saturn radii, the presence of the F ring between 2.336 and 2.371 Saturn radii and the outer radius of the A ring at 2.292 Saturn radii.

Van Allen, J. A.↗
NASA NTRS1980

Impact of Saturn ring particles on Pioneer 11

The detection of particles near the rings of Saturn by the meteoroid detection instrument on board Pioneer 11 is discussed. The instrument consists of 234 penetration detectors, distributed between two independent data channels each of which is designed to become inhibited for a period of 77 min after the registration of a penetration event in that channel. At least four particles penetrated the detectors in the 4.5 h period around Saturn periapsis at radial distances between 1.36 and 3.1 Saturn radii, a radial distribution inconsistent with the gravitational focusing of meteoroids. The detection of particles which may have been part of the E ring before the crossing of the ring plane suggests that this ring may be 1800 km thick, with an optical thickness greater than 10 to the -8th.

Humes, D. H.↗
NASA NTRS1980

Saturn's E ring revisited

Images of the E ring of Saturn obtained by the image processing of photographs of the 1966 edge-on presentation of the planet's ring plane are presented. Two methods of image enhancement were used: scanning with an image quantizer operated in the derivative mode to enhance contrast and computerized subtraction of a circularly symmetric image of the overexposed Saturn disk. Further photographic and CCD observation confirming the existence of the ring extending to twice the diameter of the A ring, which was not detected by the Pioneer 11 imaging photopolarimeter, is indicated.

Feibelman, W. A.↗
NASA NTRS1981

An Experimental Evaluation of Oil Pumping Rings

The design and construction of a reciprocating test vehicle to be used in evaluating hydrodynamic oil pumping rings are discussed. In addition, experimental test data are presented for three pumping ring designs that were constructed from Tin-Based Babbitt (SAE 11), Bearing Bronze (SAE 660), and Mechanical Carbon Graphite (Union Carbide Grade CNF-J). Data of pumped flow rate versus delivered pressure, as well as friction loss, are reported for the following conditions: frequencies of 10, 35 and 45 Hz; strokes of 25.4 mm (1.00 in.), 38.1 mm (1.50 in.) and 50.8 mm (2.00 in.) oil inlet temperature of 49 degrees (120 degrees); and pumping ring close-in pressures of 10.3 MPa (1500 lb/square inch. A 20W40 automotive oil was used for all tests. The maximum delivered pressure was 11 MPa (1600 lb/square inch. An analysis of hydrodynamic oil pumping rings was performed and the results of the analysis were compared to measured test data.

Eusepi, M. W.↗
NASA NTRS1980

An extraordinary view of Saturn's rings

A unique set of photometric and polarimetric observations made by the imaging photopolarimeter aboard the Pioneer spacecraft shortly after it penetrated the ring plane from above on its way to closest approach is reported. The bright planet limb is observed through the rings, which themselves weakly reflect direct sunlight. Polarizations range from 41% (16%) at the extreme planet limb to 2% (1.5%) at the darkest part of the B ring in the blue (red) channel. Detailed structure of the A ring is evident, most notably the Encke gap.

Burke, J. J.↗
NASA NTRS1980

Dust in Jupiter's magnetosphere. I - Physical processes. II - Origin of the ring. III - Time variations. IV - Effect on magnetospheric electrons and ions

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.

Morfill, G. E.↗
NASA NTRS1981

Effect of elastic end rings on the eigenfrequencies of thin cylinders

The effect of elastic end rings on the eigenfrequencies of thin cylindrical shells is studied by using an exact solution of the linear eigenvalue problem. The out-of-plane and torsional rigidities of the rings are responsible for the overall shell stiffness. Considerable mode interaction exists for modes with low circumferential wave numbers when the mass of the ring is comparable with that of the shell. The hypothetical simply supported and clamped boundary conditions are practically impossible to realize with a finite-mass ring for relatively short and thin shells.

El Raheb, M.↗
NASA NTRS1981

On the braids and spokes in Saturn's ring system

Two of the features in the Saturnian ring system recently observed by the Voyager 1 spacecraft are (1) the braiding of the F-ring and (2) the radial spokes that rotate across the B-ring. Both of these phenomena are explained by recognizing that the grains that constitute both the F-ring and the spokes are charged to high electrostatic potentials and are sufficiently small to be strongly affected by the magnetic field of the planet. Processes for the charging of the grains are also suggested.

Hill, J. R.↗
NASA NTRS1980

A model of the origin of the Jovian ring

Assuming that the micron-sized particles making up the bright Jovian ring are fragments of erosive collisions between micrometeoroid projectiles and large parent bodies, a physical model of the ring is calculated. This leads to a well-defined size distribution for the ejecta, whose optical properties can be compared with observation. The (most likely silicate) ejecta material maximum diameter is estimated to be 0.1 micron, and most likely the result of Io volcanic activity. The impact model's determination of ejecta size distribution in turn determines the structure of the ring, with the largest ejecta forming the bright ring, medium-sized ejecta forming a disk that extends to the Jovian atmosphere, and small ejecta forming a faint halo whose structure is dominated by electromagnetic forces.

Gruen, E.↗
NASA NTRS1981

On the radial structure of Saturn's rings

Voyager 1 cameras revealed that Saturn's B ring appears to be subdivided into hundreds of chaotically spaced narrow rings in a hierarchy that extends to the limit of resolution. A disk model is proposed and applied to Saturn's rings: it is shown that the radial diffusion in a particulate Keplerian disk, under the influence of a viscosity law that decreases more steeply with a certain surface density than with another, will promote the breakdown of the system into an ensemble of thin rings.

Ward, W. R.↗
NASA NTRS1981

Observations of the Saturn E ring and a new satellite

It is noted that the faint E ring of Saturn appears as a narrow ring 246,000 + or - 4000 km from the center of Saturn on photographs taken when the ring-plane inclination was 5.4 deg. The apparent brightness of the ring was uniform at all observed orbital longitudes and makes it possible to estimate the normal optical thickness. In addition, a faint satellite (1981S1) was observed near the L4 triangular libration point of Tethys; this satellite is probably the same object as 1980S13.

Larson, S. M.↗
NASA NTRS1982

Photopolarimetry from Voyager 2 - Preliminary results on Saturn, Titan, and the rings

The Voyager 2 photopolarimeter was reprogrammed prior to the August 1981 Saturn encounter to perform orthogonal-polarization, two-color measurements on Saturn, Titan, and the rings. Saturn's atmosphere has ultraviolet limb brightening in the mid-latitudes and pronounced polar darkening north of 65 deg N. Titan's opaque atmosphere shows strong positive polarization at all phase angles (2.7 deg to 154 deg), and no single-size spherical particle model appears to fit the data. A single radial stellar occultation of the darkened, shadowed rings indicated a ring thickness of less than 200 meters at several locations and clear evidence for density waves caused by satellite resonances. Multiple, very narrow strands of material were found in the Encke division and within the brightest single strand of the F ring.

Lane, A. L.↗
NASA NTRS1981

Application of ring tectonic theory to Mercury and other solar system bodies

It is pointed out that multiringed structures, by their presence or absence, provide a powerful tool for deciphering the thermal histories of the solid planets. The theory of ring tectonics considered by Melosh and McKinnon (1978) and Melosh et al. (1980) establishes the framework of that undertaking. The present investigation has the objective to apply this conceptualization in detail to the multiringed basins on Mercury, taking into account also a brief review concerning the current state of understanding of ring tectonics on the moon, Mars, earth, Ganymede, and Callisto. The small, icy satellites of Saturn are also discussed. The mechanics of multiple ring formation are related to the collapse of the transient basin cavity when the excavation depth and lithosphere thickness are comparable. Attention is given to the Caloris Basin on Mercury, the peak ring basins on Mercury, and the Argyre Basin on Mars.

Mckinnon, W. B.↗