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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Structure of Saturn's rings: Optical and dynamical considerations

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.

Franklin, F. A.↗
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 NTRS1983

The fine structure of the Saturnian ring system

A dust disk within a planetary magnetosphere constitutes a novel type of dust-ring current. Such an azimuthal current carrying dust disk is subject to the dusty plasma analog of the well known finite-resistivity 'tearing' mode instability in regular plasma current sheets, at long wavelengths. It is proposed that the presently observed fine ringlet of the Saturnian ring system is a relic of this process operating at cosmogonic times and breaking up the initial proto-ring (which may be regarded as an admixture of fine dust and plasma) into an ensemble of thin ringlets. It is shown that this instability develops at a rate that is many orders of magnitude faster than any other known instability, when the disk thickness reaches a value that is comparable to its present observed value.

Houpis, H. L. F.↗
NASA NTRS1984

Structure of the Uranian rings. I - Square-well model and particle-size constraints

A least squares fitting is added to the diffraction model for the Uranian rings and the model is then used to determine the relative optical depths of the rings at visible and near-IR wavelengths. Light transmission is assumed constant on a scale of a few radial km in the rings. The amount of starlight passing through the rings is calculated from occultations with account taken of a monolayer ring, diffraction effects, and multiple ring layers. A diffracted occultation profile is generated with consideration given to the angular diameter of the star, the impulse response of the detector, and atmospheric aberrations. Calculation procedures which remove noise are outlined and results are compared with the observational data base. The wavelength dependence of optical depth is formulated. It is shown that occultation data do not support the presence of a large fraction of submicron particles. No optical depth variations are projected for 0.88-2.2 microns wavelengths. Unchopped data are needed to verify the model predictions.

Elliot, J. L.↗
NASA NTRS1985

Bending waves and the structure of Saturn's rings

The surface mass density profiles at four locations within Saturn's rings are calculated using Voyager spacecraft images of spiral bending waves. The identification of a feature in Saturn's outer B ring as Mimas's 4:2 bending waves is confirmed, and these 4:2 waves are analyzed to determine the surface density in Saturn's B ring. A fourth set of bending waves, the Mimas 7:4, located in the inner A ring, is identified and analyzed. Mimas's 5:3 and 8:5 bending waves, observed in the middle and outer A ring respectively, are reanalyzed.

Lissauer, J. J.↗
NASA NTRS1986

Structure of the Uranian rings. II - Ring orbits and widths

A square-well model was used to calculate the midtimes, widths and optical depths at visible and IR wavelengths of the nine Uranian rings based on 13 occultation measurements from 1977-1983. Many of the measurement campaigns contained data from repeated crossings. An improved kinematical model is developed for the ring system, noting that the gamma and delta rings were confirmed to depart from Keplerian ellipses. Upper limits are calculated for the sizes of shepherd satellites of various potential densities. The ring width determinations demonstrate the existence of significant width perturbations in the rings, which all displayed particle shadowing.

French, R. G.↗
NASA NTRS1991

Resonance structures in Saturn's rings probed by radio occultation. I - Methods and examples

Individual and comparative analyses are conducted for 29 of the wavelike features revealed by optical depth profiles of Saturn's rings; of these, 18 are in Ring A, one is in Ring B, and 10 are in Ring C. Only 20 of these were identifiable with known resonances, and all eight of the unexplained wave features are in Ring C. For 14 weak density waves in Ring A, a linear density wave theory modeling of the waveform near resonance yields independent estimates of the surface mass density together with reliable estimates of resonance location.

Rosen, Paul A.↗
NASA NTRS1986

Nonlinear density waves in planetary rings

The steady-state structure of planetary rings in the presence of density waves at the Lindblad resonances of a satellite is indicated. The study is based on the dispersion relation and damping rate for nonlinear density waves, derived by Shu et al. (1985) and by Borderies, Goldreich, and Tremaine (1985). It is shown that strong density waves lead to an enhancement of the background surface density in the wave zone.

Borderies, Nicole↗
NASA NTRS2006

Optical and Mechanical Properties of Glass Blown In Vacuo

Theoretically, the strength of glass processed in vacuum should be higher due to outgassing of contaminants normally present in the glass, such as bulk water in the form of OH bonds that tends to weaken the glass structure. In this research, small discs of a few types of glass have been subjected to various temperatures for extended periods of time in vacuum. Their strength was then tested using a standard flexure technique, facilitated by a custom-designed test fixture, and the results were compared to glass tested in air using the same fixture. The purpose of the glass blowing investigation was to prove the basic feasibility of a high-level concept for in-space manufacture of optical elements. The central requirement was that the glass bubble had to be blown into a support structure such that the bubble could be handled by manipulation of the structure. The blown bubble attached itself to a mullite ring geometrically and mechanically, as a demonstration in the initial experiments described here, by expanding through and around it. The vacuum system used was custom made, as were most of the components of the system, such as the heating element, the glass and ring support structure, and the gas inlet system that provided the pressure needed to blow the glass.

Manning, andrew↗
NASA NTRS1981

Moonlets in Saturn's rings

The brightness structure within Cassini's division in Saturn's rings is explained in terms of perturbations produced by moonlets embedded within an optically thin disk of smaller ring particles. The moonlets exert gravitational torques on neighboring ring particles and create gaps; diffusion acts to fill the gaps. A new explanation is offered for the inner edge of the Cassini division being located at the 2:1 resonance with Mimas.

Lissauer, J. J.↗
NASA NTRS1986

Structure and evolution of Saturn's rings

It is noted that many Voyager observations on the structure and evolution of Saturn's rings remain largely unexplained. The variation of ring thickness and particle size with composition may be partly explained by the input of density waves in the 'heating' of such rings as the outer A ring; in addition, the particles appear to resemble Weidenschilling et al.'s (1984) 'ephemeral bodies' rather than chunks of ice. It is suggested that many current difficulties may be resolved by positing that at least ring A is young, having been created by the destruction of one of the ring moons.

Esposito, L. W.↗
NASA NTRS1976

Photoionization and ion cyclotron resonance studies of the ion chemistry of ethylene oxide

The formation of the ethylene oxide molecular ion and its subsequent ion-molecule reactions leading to the products C2H5O(+) and C3H5O(+) have been studied using time-resolved photoionization mass spectroscopy, ion cyclotron resonance spectroscopy, and photoelectron spectroscopy. An examination of the effects of internal energy on reactivity shows that the ratio of C3H5O(+) to C2H5O(+) increases by an order of magnitude with a single quantum of vibrational energy. The formation of (C2H4O/+/)-asterisk in a collision-induced isomerization is found which yields a ring-opened structure by C-C bond cleavage. The relaxed ring-opened C2H4O(+) ion reacts with neutral ethylene oxide by CH2(+) transfer to yield an intermediate product ion C3H6O(+) which gives C3H5O(+) by loss of H.

Corderman, R. R.↗