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NASA NTRS1982

Effects of differential rotation on the gravitational figures of Jupiter and Saturn

It is assumed that observed zonal currents in the atmospheres of Jupiter and Saturn correspond to a state of permanent rotation, and that the angular velocity is constant on cylindrical surfaces parallel to the rotation axis. The equation of hydrostatic equilibrium for a rotating planet is solved under these restrictive assumptions, and the effect of the hypothesized rotation state on the planet's gravity harmonics and external shape is investigated. Spacecraft data on zonal currents are used to derive nearly model-independent corrections to the first four zonal gravity harmonic coefficients, which can be used to correct observed gravity harmonics to values appropriate for solid-body rotation. If the assumed rotation state is applicable, then zonal currents lead to measurable topography of isopycnic surfaces with respect to the reference figure defined by the magnetospheric rotation period and the gravity harmonics. The amplitude of the topography is on the order of 5 km for Jupiter and 60 km for Saturn.

Hubbard, W. B.↗

NASA NTRS1999

Cassini Radio Science Experiments on Saturn and Titan Preserved Because of Lewis Analysis

The Cassini mission to Saturn is an international venture with participation from NASA, the European Space Agency, and the Italian Space Agency. The Cassini spacecraft was launched from Cape Canaveral in October 1997 and is scheduled to arrive at Saturn in July 2004. After arrival, the spacecraft will orbit Saturn about 60 times over a period of 4 years. During this time, the Cassini Radio Science Subsystem will be used to investigate the atmosphere and rings of Saturn and the atmosphere of its largest moon, Titan--which is larger than Mercury and is the only moon in our solar system with a dense atmosphere. A critical component in Cassini s Radio Science Subsystem is a traveling-wave tube (TWT) that was designed at the NASA Lewis Research Center and built by Hughes Electronic Dynamics Division (ref. 1). This TWT will amplify downlink microwave signals at a frequency of 32 GHz for the Deep Space Network and will be involved in a number of experiments. These include occultation experiments in which the microwave signal will be beamed through rings and atmospheres toward Earth. Researchers will analyze the received signals to determine the sizes and distributions of the particles in the rings and the structure and composition of the atmospheres. The Radio Science Subsystem also will also be used to more accurately determine the mass and size of Saturn and its moons, to investigate the solar corona, and to search for gravity waves from outside the solar system.

Wilson, Jeffrey D.↗

NASA NTRS1975

Saturn's 3 nu 3 methane band - An analysis in terms of a scattering atmosphere

Using parameters recently measured in the laboratory, the shapes of manifolds belonging to the R-branch of Saturn's 3 nu 3 CH4 band were analyzed in terms of a homogeneous scattering model of Saturn's atmosphere, and the results were compared with those of an earlier analysis in terms of a reflecting-layer model. The resulting effective pressure is an order of magnitude smaller than for the reflecting-layer analysis, and the C/H ratio is an order of magnitude higher than the solar value. The overall fit of the theoretical profiles to the observed manifold shapes is distinctly worse, especially for R(7). Scattering evidently plays only a minor role in the formation of this band along Saturn's south-central meridian.

Trafton, L.↗

NASA NTRS1974

The Mariner Jupiter/Saturn ultraviolet experiment

Atmospheric properties of Saturn's rings as measured by an ultraviolet spectrometer onboard the Mariner Jupiter/Saturn probe are studied. Measurements were made of planetary atmospheric radiation, resonance scattered by atomic or molecular constituents, solar spectra, and the absorption characteristics of the atmosphere. Measurements were made in the 400 to 1600 A region.

Broadfoot, A. L.↗

NASA NTRS1989

The far ultraviolet reflection spectrum of Uranus - Results from the Voyager encounter

The present analysis of the 1250-1700 A region Uranus spectrum obtained by Voyager's US spectrometer characterizes these observation results as due primarily to solar light reflected from an H2 Rayleigh and Raman scattering atmosphere with small but measurable hydrocarbon absorption. The hydrocarbon abundances obtained are substantially lower than those at comparable levels of the Saturn or Jupiter atmospheres; it is suggested, in one-dimensional terms, that this is due to diffusive separation, in conjunction with photochemical depletion caused by a very low eddy-diffusion coefficient. Strong latitudinal variations in the hydrocarbon abundances are suggested in the subsolar, polar stratosphere.

Yelle, Roger V.↗

NASA NTRS1993

Vertical structure models of the 1990 equatorial disturbance on Saturn

In September 1990, an atmospheric disturbance in the form of an abnormally high albedo area developed in the equatorial region of Saturn. Events of this nature are exceedingly rare for this planet as they have been detected in the equatorial region on only two other occasions in over a century. In ongoing monitoring of the atmospheres of the outer planets, CCD imaging observations of Saturn by New Mexico State University's Tortugas Mountain Station were made before, during, and after the disturbance's formation through both broad-band filters and narrow-band visible/near-IR filters centered in methane absorption bands. Also, multispectral Hubble Space Telescope observations were made within weeks of the event and later in 1991. These observations were calibrated and scans of reflectivity at constant latitude are being modeled with a vertically inhomogeneous, multiple scattering model previously used to model Jupiter's South Equatorial Belt brightening event in 1989. In addition, the reflectivity of the disturbance as a function of the scattering angles is being obtained so as to model this feature's vertical structure in particular. A preliminary report of the modeling results will be presented.

Kuehn, D. M.↗

NASA NTRS1986

The Voyager 2 encounter with the Uranian system

Discoveries which have occurred due to the success of the Voyager 2 flyby of Uranus and its moons are summarized, along with techniques used to maximize the data collected and minimize the demands on the spacecraft. The 11 spacecraft science packages, including photopolarimeters, spectrometers, a magnetometer, radios and a charged particle detector gathered information on the ring system, the scattering, emitting and reflecting characteristics of the Uranian atmosphere, and the five major satellites. The data revealed 10 minor satellites between Miranda and Uranus and the similarities between the Uranus, Saturn and Jupiter atmospheres. Extensive tabular data are provided for the physical dimensions of the nine rings and the 15 satellites. Finally, data on the magnetosphere and upper atmosphere environment of Uranus and imagery of the major moons are discussed.

Stone, E. C.↗

NASA NTRS2000

Innovative Balloon Buoyancy Techniques for Atmospheric Exploration

Until quite recently, the only practical means to control balloon buoyancy, and thus altitude, required consuming large amounts of fuel or the limited venting of helium balloons and/or dropping of ballast. With recent discoveries at JPL, novel long-life, balloon buoyancy techniques have been discovered that for the first time allow balloons to float in the primarily hydrogen atmospheres of Jupiter, Saturn, Uranus, and Neptune (using ambient fill-gas), and by using renewable energy sources, allow multiple controlled landings on Venus (using atmospheric temperature differences), Mars (solar heat), Titan (RTG heat), and Earth (planet radiant heat).

Balloon Planetary Aerobot Buoyancy Mars Titan Venu↗

NASA NTRS1994

Infrared spectroscopy of Jupiter and Saturn

Infrared spectroscopy provides unique insights into the chemistry and dynamics of the atmospheres of Jupiter and Saturn -- and of Titan, the enigmatic satellite of Saturn. The 5 micron spectral region of these objects is transparent to deep levels, and is therefore particularly useful for the identification of molecules in the deep atmosphere at very low (parts per billion) concentrations. In 1991 we obtained data at J, H, K, and M and made repeated observations of Titan's albedo as the satellite orbited Saturn. The J albedo is 12 + -3% greater than the albedo measured in 1979; the H and K albedos are the same. There was no evidence for variations at any wavelength over the eastern half of Titan's orbit. We also obtained low resolution (R = 50) spectra of Titan between 3.1 and 5.1 microns. The spectra contain evidence for CO and CH3D absorptions. Spectra of Callisto and Ganymede in the 4.5 micron spectral region are featureless and give albedos of 0.08 and 0.04 respectively. If Titan's atmosphere is transparent near 5 microns, its surface albedo there is similar to Callisto's. In 1992 and 1993 we obtained further spectroscopic data of Titan with the UKIRT CGS4 spectrometer. We discovered two unexpected and unexplained spectral features in the 3-4 micron /spectrum of Titan. An apparent emission feature near the 3 micron (nu3) band of methane indicates temperatures higher than known to be present in Titan's upper stratosphere and may be caused by unexpected non-LTE emission. An absorption feature near 3.47 microns may be caused by absorption in solid grains or aerosol's in Titan's clouds. The feature is similar, but not identical to organics in the interstellar matter and in comets.

Knacke, Roger F.↗

NASA NTRS1980

Ultraviolet photometer observations of the Saturnian system

Several interesting cloud and atmospheric features of the Saturn system have been observed by the long-wavelength channel of the two-channel ultraviolet photometer aboard the Pioneer Saturn spacecraft. Reported are observations of the most obvious features, including a Titan-associated cloud, a ring cloud, and the variation of atmospheric emission across Saturn's disk. The long-wavelength data for Titan suggest that a cloud of atomic hydrogen extends at least 5 Saturn radii along its orbit and about 1.5 Saturn radii vertically. A ring cloud, thought to be atomic hydrogen, has also been observed by the long-wavelength channel of the photometer; it shows significant enhancement in the vicinity of the B ring. Finally, spatially resolved observations of Saturn's disk show significant latitudinal variation. Possible explanations of the variation include aurora or limb brightening.

Judge, D. L.↗

NASA NTRS1980

Voyager Encounters Saturn: Scientific Highlights

Observations generated by Voyager 1's encounter with Saturn are disclosed. Atmospheric conditions, the rings, new moons and the five inner moons are described. Titan, Hyperion and Iapetus are discussed in detail, as is Saturn's magnetosphere.

Source record↗

NASA NTRS1992

The Composite Infrared Spectrometer

The Composite Infrared Spectrometer (CIRS) is a remote sensing instrument to be flown on the Cassini orbiter. It contains two Fourier transform spectrometers covering wavelengths of 7-1000 microns. The instrument is expected to have higher spectral resolution, smaller field of view, and better signal-to-noise performance than its counterpart, IRIS, on the Voyager missions. These improvements allow the study of the variability of the composition and temperature of the atmospheres of both Saturn and Titan with latitude, longitude and height, as well as allowing the possibility of discovery of previously undetected chemical species in these atmospheres. The long wavelengths accessible to CIRS allow sounding deeper into both atmospheres than was possible with IRIS.

Calcutt, Simon↗

NASA NTRS1978

Voyager radio occultation investigations at Saturn

Voyager will use dual-frequency 3.5 and 13 cm wavelength radio occultation techniques to study the atmospheres and ionospheres of Saturn and Titan, and the rings of Saturn. At Titan radio occultation is predicted to probe the atmosphere to the surface. The existence of a surface could be confirmed by detection of an obliquely scattered echo. At Saturn the two Voyager encounters will provide occultation measurements of temperate and equatorial regions of the atmosphere and ionosphere, and of the rings. The atmosphere will also be probed in polar regions during the deepest portions of the occultation. Both frequency and intensity data will be collected and jointly analyzed to study temperature-pressure profiles, and to derive information on atmospheric shape, turbulence, and weather. For the rings, Voyager will provide measurements of the complex (amplitude and phase) radio extinction and angular scattering functions of the ring particles as a function of wavelength, polarization, and radial distance from Saturn.

Tyler, G. L.↗

NASA NTRS2017

Diving Deeper: Exploring the Feasibility of Lowering Cassini’s Final Orbits

During the final five orbits of Cassini’s mission, the spacecraft will get closer to Saturn than it has ever been. These five orbits were designed to be as deep in the atmosphere as Cassini could safely fly; however, recent occultation data of Saturn’s atmosphere suggest that it is contracting. Given this contraction, the primary concern during these orbits has shifted from spacecraft health and safety to loss of science value. This paper explores a scenario for modifying the Cassini spacecraft’s trajectory, during these final orbits, such that it dips deeper into Saturn’s atmosphere. This scenario describes the method for in-situ detection of Saturn’s atmospheric state, the locations and sizes of maneuvers that would reduce the final periapsis altitudes, the effects of such maneuvers on the remaining trajectory, and the risks involved. The result is that a periapsis-lowering, “pop-down” maneuver is feasible during Cassini’s final orbits. Risk to the spacecraft is minimized by using the attitude control thrusters as density detectors during the first three atmospheric transits of the final five orbits. Should these transits reveal sufficiently low density and should sufficient propellant remain, then the Cassini project will consider performing the maneuver.

Sturm, Erick J., II↗

NASA NTRS1976

An analysis of Saturn's methane 3 nu /3/ band profiles in terms of an inhomogeneous atmosphere

Observed profiles of the R branch of Saturn's CH4 3 nu (3) band are compared with synthetic profiles computed from inhomogeneous models which are consistent with Saturn's H2 quadrupole-line equivalent widths. A C/H ratio approximately three times the solar value and a CH4 abundance of about 100 m am are found. Scattering plays a significant role in the formation of manifold profiles below a depth where the H2 abundance is 20-30 km am.

Macy, W., Jr.↗

NASA NTRS1974

Gaseous toroid around Saturn

The trapping of Titan's escaping atmosphere in the Saturnian system by a toroidal ring is discussed. The radius of the toroid is comparable to Titan's orbit, or about ten times larger than the visible rings. Theoretical atmospheric models are formulated that consider Saturn's gravitational attraction and magnetospheric properties in forming this toroid and in protecting toroid particles from direct ionization by solar wind particles.

Mcdonough, T. R.↗

NASA NTRS1972

Thermal radio emission from Jupiter and Saturn

Microwave brightness temperature calculations have been carried out for a number of model atmospheres for Jupiter and Saturn. The models considered are characterized by helium to hydrogen number mixing ratios which range from 0 to 0.2. Gaseous ammonia is assumed to be a trace constituent in all the models. The ammonia abundance below the (NH3) cloud level is a free parameter which is determined by comparing the observed thermal spectrum of Jupiter and the total spectrum of Saturn with the model calculations. The theoretical microwave spectra corresponding to those models in which the ammonia abundance is that expected from an atmosphere containing a solar abundance of elements are found to be in generally good agreement with the observations. This result is shown to be nearly independent of the helium to hydrogen ratio for the models considered. There is no evidence at this time that a non-thermal component contributes to Saturn's microwave spectrum.

Gulkis, S.↗

NASA NTRS1991

Infrared variability of Jupiter and Saturn

Infrared spectroscopy provides unique insights into the chemistry and dynamics of the atmospheres of Jupiter and Saturn, and of the enigmatic satellite of Saturn, Titan. The 5 micron spectral region of these objects is transparent to deep levels, and is therefore particularly useful for the identification of molecules that are present at very low (parts per billion) concentrations. In Titan, 5 micron observations probe atmospheric layers at or near the surface. Ground-based spectroscopy complements Voyager, Galileo, and Cassini measurements. The spectroscopy is sensitive to lower mixing ratios for selected molecules, while the on-board mass and infrared spectrometers probe molecules and levels that are inaccessible form the ground. The observations also provide time-based data for preparation of the upcoming missions.

Knacke, Roger↗