Search NASA⌕ Search

SEARCH · Search NASA

Results for “Tethys”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Orbit-orbit resonances in the solar system - Varieties and similarities

Descriptions of various orbit-orbit resonance mechanisms in the solar system are brought together in such a manner that the physical processes underlying the traditional mathematical presentations are apparent. A simple qualitative model based on the resonance between Saturn's satellites Titan and Hyperion is presented, the same resonance is analyzed quantitatively, and the small-eccentricity mechanism is examined. The following resonances are investigated in detail: Enceladus-Dione, Mimas-Tethys, Neptune-Pluto, and Rhea-Titan (secular resonance). Coupled librations of several asteroids near mean motions commensurable with Jupiter's are modeled, the Laplace relation involving Io, Europa, and Ganymede is studied, and the 1:1 resonance between the Trojan asteroids and Jupiter is discussed. Some higher-order commensurabilities involving asteroids are considered, including the 3:1 resonance between Alinda and Jupiter, the 13:5 resonance of Toro with Venus, the 8:5 resonance of Toro with earth, and the 11:28 resonance of Ivar with earth.

Greenberg, R.↗
NASA NTRS1978

The formation of the Cassini division in Saturn's rings

An explanation for the size and location of the Cassini division in Saturn's rings is proposed. The explanation is based on the collective response of the particles in the ring to the resonant forcing by Mimas. An upper limit is calculated for the width of the gap that could be opened at a resonance. In addition, an estimate is obtained regarding the damping of the density waves by viscous and nonlinear effects. A picture is presented of the development of a gap. The results are compared with the observed properties of the divisions in Saturn's rings. The exact position of the inner edge of the Cassini division is difficult to predict, because the 2:1 resonance lies very near several weaker resonances (4:2 and 6:3 with Mimas, 4:1 with Tethys). However, the edge should lie near 17 seconds, and this is consistent with ground based observations.

Goldreich, P.↗
NASA NTRS1979

Orbital theories of outer planet satellites

An analytical theory of Mimas and Tethys was developed, retaining terms which produce perturbations of the order of + or - 10 km. The theory uses a novel set of variables, and was developed with the Hori-Lie algorithm, using the algebraic manipulation language TRIGMAN. the perturbations were implemented by means of FORTRAN subroutines produced by the computer.

Jefferys, W. H.↗
NASA NTRS1979

Theories of resonant satellite pairs in Saturn's system

Analytical theories have been devised for the three resonant pairs in Saturn's satellite system: Enceladus-Dione, Titan-Hyperion, and Mimas-Tethys. An algebraic manipulation language was adopted to calculate the theories; use of the canonically invariant Hori-Lie (1966) theory in noncanonical variables made it possible to perform direct computations of perturbations in such quantities as longitude, latitude and radius vector. Important terms at the 1-100 km level have been found second-order terms of the resonant satellite are calculated.

Jefferys, W. H.↗
NASA NTRS1979

Pioneer Saturn Encounter

The Pioneer Saturn Spacecraft, which began its journey as Pioneer 11, provided the first close view of the rings of Saturn as well as its system of moons. Its payload of 11 operating instruments obtained or confirmed data about the mass, temperature, composition, radiation belts, and atmosphere of the planet and its larger satellite, Titan. It made photometric and polarization measurements of lapetus, Rhea, Dione, and Tethys, as well as discovered additional rings. Scientific highlights of the mission are summarized. Color imagery provided by the photopolarimeter is included along with illustrations of the planet's magnetic field and radiation belts.

Source record↗
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

Observations of energetic ions and electrons in Saturn's magnetosphere

Observations of the magnetosphere of Saturn made by the cosmic-ray experiment on board Pioneer 11 are summarized. Detailed energy spectra and angular distributions of protons from 0.2 to 22 MeV and electrons from 0.1 to 2 MeV were obtained, together with measurements of helium nuclei between 0.65 and 22 MeV/n. The time histories of proton and electron data suggest a division of the Saturn magnetosphere into three regions: (1) an outer magnetosphere between 17 and 7.5 Saturn radii, which is characterized by monotonically increasing fluxes and spectral hardening inward from the magnetosphere, with large changes in low-energy electron angular distributions; (2) a slot region between 7.5 and 4 Saturn radii where marked decreases in proton and low-energy electron fluxes are observed, apparently due to the presence of Dione, Tethys and Enceladus; and (3) an inner region between 4 Saturn radii and the ring edge, which exhibits sharp increases in proton fluxes with energies up to 20 MeV, which are broken near the orbits of Mimas, Janus and possibly S 11. A sharp cutoff of proton and electron fluxes is observed just beyond the nominal edge of the A ring.

Trainor, J. H.↗
NASA NTRS1980

Tidal dissipation, orbital evolution, and the nature of Saturn's inner satellites

Estimates of tidal damping times of the orbital eccentricities of Saturn's inner satellites place constraints on some satellite rigidities and dissipation functions Q. These constraints favor rock-like rather than ice-like properties for Mimas and probably Dione. Photometric and other observational data are consistent with relatively higher densities for these two satellites, but require lower densities for Tethys, Enceladus, and Rhea. This leads to a nonmonotonic density distribution for Saturn's inner satellites, apparently determined by different mass fractions of rocky materials. In spite of the consequences of tidal dissipation for the orbital eccentricity decay and implications for satellite compositions, tidal heating is not an important contributor to the thermal history of any Saturnian satellite.

Peale, S. J.↗
NASA NTRS1980

Plasmas in Saturn's magnetosphere

Passage of Pioneer 11 through Saturn's magnetosphere revealed a third magnetosphere with a high plasma abundance. The dominant ion species appears to be oxygen. The plasma is located in a large torus about Saturn, including the orbits of Dione and Tethys. The plasma are rigidly corotating with the planet to distances of at least 10 Saturn radii. Bulk flows appear to move in the corotation direction, but at speeds lower than those expected from rigid corotation. The ions appear to be the ionization products of water frost on the surface of the ring material.

Frank, L. A.↗
NASA NTRS1980

Observations of extreme ultraviolet emissions from the Saturnian plasmasphere

Emission signals from the Saturnian plasmasphere at wavelengths shortward of 800 A have been detected by the Pioneer ultraviolet photometer. The surface brightness of the emissions is about 0.3 + or - 0.2 R. These short-wavelength emissions are interpreted as arising primarily from the radiative decay of electron-excited atomic oxygen ions (O(2+)), in the region between 5 and 7 Saturn radii from Saturn. The total power radiated by the Saturnian plasma inferred from these ultraviolet measurements is about 2 x 10 to the 16th erg/sec, consistent with in situ plasma measurements. From the observed energy loss rate it is estimated that the ions are introduced into the plasma torus at a rate of 8 x 10 to the 25th ions/sec, possibly through the sputtering of water ice on the surface of Tethys and Dione by particle impact.

Wu, F. M.↗
NASA NTRS1981

Saturn gravity results obtained from Pioneer 11 tracking data and earth-based Saturn satellite data

Improved gravity coefficients for Saturn, its satellites and rings are calculated on the basis of a combination of Pioneer 11 spacecraft Doppler tracking data and earth-based determinations of Saturn natural satellite apse and node rates. Solutions are first obtained separately from the coherent Doppler tracking data obtained for the interval from August 20 to September 4, surrounding the time of closest approach, with the effects of solar plasma on radio signal propagation taken into account, and from secular rates for Mimas, Enceladus, Tethys, Dione, Rhea and Titan determined from astrometric data by Kozai (1957, 1976) and Garcia (1972). Combination of the data by the use of the Pioneer solution and corresponding unadjusted covariance matrix as a priori information for a secular rate analysis results in values for the total ring mass of essentially zero at a standard error level of 1.7 x 10 to the -6th Saturn masses, a ratio of solar mass to that of the Saturn system of 3498.09 + or - 0.22, masses of Rhea, Titan and Iapetus of 4.0 + or - 0.9, 238.8 + or - 3, and 3.4 + or - 1.3 x 10 to the -6th Saturn masses, respectively, and second and fourth zonal harmonics of 16,479 + or - 18 and -937 + or - 38, respectively. The harmonic coefficients are noted to be important as boundary conditions in the modeling of the Saturn interior.

Null, G. W.↗
NASA NTRS1981

Narrowband electromagnetic emissions from Saturn's magnetosphere

A series of narrowband electromagnetic emissions were detected by the plasma wave instrument on board Voyager 1 coming from the inner region of Saturn's magnetosphere in the frequency range 3-30 kHz. These emissions have many similarities to continuum radiation detected in the earth's magnetosphere and narrowband kilometric radiation in the Jovian magnetosphere. The observed frequency spacing suggests that the emissions are being generated near Tethys, Dione and Rhea, probably in regions of large plasma density gradients associated with boundaries of the plasma sheet.

Gurnett, D. A.↗
NASA NTRS1981

Theory of satellite orbit-orbit resonance

On the basis of the strong mathematical and physical parallels between orbit-orbit and spin-orbit resonances, the dynamics of mutual orbit perturbations between two satellites about a massive planet are examined, exploiting an approach previously adopted in the study of spin-orbit coupling. Resonances are found to exist when the mean orbital periods are commensurable with respect to some rotating axis, which condition also involves the apsidal and nodal motions of both satellites. In any resonant state the satellites are effectively trapped in separate potential wells, and a single variable is found to describe the simultaneous librations of both satellites. The librations in longitude are 180 deg out-of-phase, with fixed amplitude ratio that depends only on their relative masses and semimajor axes. The theory is applicable to Saturn's resonant pairs Titan-Hyperion and Mimas-Tethys, and in these cases the calculated libration periods are in reasonably good agreement with the observed periods.

Blitzer, L.↗
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

Voyager 2 encounter with the Saturnian system

An overview is presented of the encounter of Voyager 2 with the Saturnian system. Following an indication of the spacecraft trajectory through the Saturn system on its way to a 1986 encounter with Uranus, and the design and operation of the Voyager 2 scientific instruments, attention is given to the major scientific results of the encounters. These results include observations of similarities between the atmospheres of Saturn and Jupiter, studies of gaps in the rings and the eccentric ringlets within the gaps, imaging of the ring systems and satellites, particularly Phoebe, Iapetus, Hyperion, Tethys, Enceladus and the atmosphere of Titan, and studies of magnetospheric structures and dynamics responsible for Saturn radio emission.

Stone, E. C.↗
NASA NTRS1982

Energetic charged particles in Saturn's magnetosphere - Voyager 2 results

Results from the cosmic-ray system on Voyager 2 in Saturn's magnetosphere are presented. During the inbound pass through the outer magnetosphere, the not less than 0.43-million-electron-volt proton flux was more intense, and both the proton and electron fluxes were more variable, than previously observed. These changes are attributed to the influence on the magnetosphere of variations in the solar wind conditions. Outbound, beyond 18 Saturn radii, impulsive bursts of 0.14to greater than 1.0-million-electron-volt electrons were observed. In the inner magnetosphere, the charged particle absorption signatures of Mimas, Enceladus, and Tethys are used to constrain the possible tilt and offset of Saturn's internal magnetic dipole. At approximately 3 Saturn radii, a transient decrease was observed in the electron flux which was not due to Mimas. Characteristics of this decrease suggest the existence of additional material, perhaps another satellite, in the orbit of Mimas.

Vogt, R. E.↗
NASA NTRS1982

Volcanism and igneous processes in small icy satellites

Evidence for the production of endogenic processes of the small Saturnian satellites by igneous activity of low melting point NH3-H2O magma heated radiogenically is presented. An initial state of the inner satellites is modeled as a homogeneous mixture of particulate silicates and ices. Conductive transport is assumed to have either combined with heat capacity in a mixture of crystalline phases, or to have been reduced by the presence of dust, defects, vitreous or amorphous phases, and clathrates. The extent to which a eutectic melt could form is calculated in terms of the volume percentage of melt, with all heating above 175 K going toward overcoming the latent heat of the eutectic mix. Mimas and Enceladus were treated as free from radiogenic heat sources, which were significant for Tethys, Dione, Rhea, and Iapetus. The migrations of inner materials to form surface structures and seal off the interiors of the moons are described.

Stevenson, D. J.↗
NASA NTRS1982

The magnetosphere of Saturn

Information about the magnetosphere of Saturn is provided: the magnetic dipole moment is axisymmetric, the bow shock stand-off distance is about 22 R sub S. The satellites Titan, Dione, and Tethys are probably the primary sources of magnetospheric plasma. Outside of approx. 4 R sub S, energetic particles are energized by diffusing inward while conserving their first and second adiabatic invariants. Particles are lost by satellite sweep-out, absorption byt the E ring and probably also by plasma interactions. The inner magnetosphere is characterized.

Schardt, A. W.↗