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At least 1,207 records · Page 67
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NASA NTRS1976

The far ultraviolet /1200-1900 A/ spectrum of Jupiter obtained with a rocket-borne multichannel spectrometer

Far-ultraviolet spectra of Jupiter with a significant improvement in sensitivity and spectral resolution have been obtained from a sounding rocket by using a 10-channel spectrometer behind a pointing telescope. The major results obtained from these spectra are: (1) measurement of the Jovian H I 1216-A brightness (a comparison with other measurements indicates that the Ly-alpha emission is likely to be variable); (2) measurement of the wavelength-dependent albedo for Rayleigh-scattered solar radiation from about 1550 to 1875 A with approximately 25-A resolution, making it possible to set revised upper limits on the abundances of some of the minor constituents in the upper Jovian atmosphere; and (3) a demonstration that weak emissions between approximately 1250 and 1500 A and near 1600 A are probably the Lyman bands of H2 excited by low-energy electrons.

Giles, J. W.↗
NASA NTRS1976

The magnetic field of Jupiter

The paper is concerned mainly with the intrinsic planetary field which dominates the inner magnetosphere up to a distance of 10 to 12 Jovian radii where other phenomena, such as ring currents and diamagnetic effects of trapped charged particles, become significant. The main magnetic field of Jupiter as determined by in-situ observations by Pioner 10 and 11 is found to be relatively more complex than a simple offset tilted dipole. Deviations from a simple dipole geometry lead to distortions of the charged particle L shells and warping of the magnetic equator. Enhanced absorption effects associated with Io and Amalthea are predicted. The results are consistent with the conclusions derived from extensive radio observations at decimetric and decametric wavelengths for the planetary field.

Acuna, M. H.↗
NASA NTRS1977

Observations of NH3 in the atmosphere of Jupiter during 1973, 1974

The 6450 A ammonia absorption band in the atmosphere of Jupiter was observed during the summers of 1973 and 1974. High-dispersion spectra of this band were obtained and analyzed on a line-by-line basis to derive ammonia abundances in the Jovian atmosphere. The abundances determined this way show strikingly large fluctuations.

Young, K. A.↗
NASA NTRS1977

Observations of Jupiter and Saturn at 5-8 micron

Moderate-resolution spectrophotometry (about 0.015) has shown the effects of known atmospheric constituents (NH3, CH4, C2H6) on the 5-8 micron spectrum of Jupiter. Broadband observations of Saturn at 6.5 micron are also reported.

Russell, R. W.↗
NASA NTRS1977

Infrared observations of Jupiter cloud zones

Images of Jupiter have been obtained at three wavelengths intervals in the infrared: 0.7-2.5, 1.2-1.3, and 1.5-1.7 micron. The images show evidence for two distinct zones of high-altitude clouds; one at 10 deg N, the other at 22 deg S. The cloud zones also appear to be at different heights in the atmosphere and to have particles with different scattering properties.

Davies, D. W.↗
NASA NTRS1977

Turbulent viscosity and Jupiter's tidal Q

A recent estimate of tidal dissipation by turbulent viscosity in Jupiter's convective interior predicts that the current value of the planet's tidal Q is roughly 5 million. We point out a fundamental error in this calculation, and show that turbulent dissipation alone implies that at present Q is about 50 trillion. Our reduced estimate for the rate of tidal dissipation shows conclusively that tidal torques have produced only negligible modifications of the orbits of the Galilean satellites over the age of the solar system.

Goldreich, P.↗
NASA NTRS1977

de Sitter's theory flattens Jupiter

The discrepancy between values of Jupiter's dynamic oblateness as measured by space probes and via 1971 beta Sco occultations is re-examined. The indicated correction to the Io ephemeris is compared to corrections proposed by Aksnes and Franklin (1975, 1976). It is found that the latter corrections reduce the above discrepancy to a marginal level.

Hubbard, W. B.↗
NASA NTRS1977

Mariner-Jupiter-Saturn Low Energy Charged Particle Experiment

The Low Energy Charged Particle Experiment will be launched on the Mariner-Jupiter-Saturn spacecraft in August 1977. The experiment has been designed to perform particle measurements in the intense radiation belts of the Jovian and Saturnian environments, and to provide detailed spectral analysis of both solar and galactic particles in interplanetary space. A single instrument uses 23 solid-state detectors configured in two distinct detector subsystems: one optimized for interplanetary and interstellar measurements, the other for specific particle species, energies, and intensities expected near the planets.

Peletier, D. P.↗
NASA NTRS1976

Attitude control of Mariner Jupiter-Saturn spacecraft

A major challenge of the Mariner Jupiter-Saturn '77 spacecraft was devising a suboptimal attitude controller that could meet the demanding mission requirements. The challenge was met by implementing a discrete stochastic controller for a specially designed onboard computer. The paper describes the design and operation of the controller, based on a simple model of spacecraft dynamics. Two types of cruising modes are considered: inertial cruise, where spacecraft attitude is determined from gyro position outputs, and celestial cruise, where position information is obtained from sun sensors and a star tracker. These two cruise modes under conditions of disturbances were simulated on computer, and the results showed that the controller maintained the spacecraft attitude with low rates. An appendix gives details on the single-step predictor.

Bahrami, K. A.↗
NASA NTRS1977

Infrared imaging of Jupiter in the 8-14-micrometer spectral region

High-spatial-resolution images of Jupiter were produced on the Hale 200-in. telescope. A programmable wobbling secondary was used to raster-scan the planet with 64 by 64 1-arcsec pixels. Images were made with broadband (8-14 microns) and several 1- and 2-micron-wide filters. All images reveal a belt-and-ozone structure similar to visible photographs. Belts in the broadband data appear to be about 2 K hotter than zones, but contrast varies markedly in different parts of the 8-14-micron spectral region. The lowest belt-zone contrast is found in the hydrogen-opacity-dominated region at 12.5 microns, while images at 9.5 microns exhibit the greatest contrast. Isolated areas are observed to be as much as 4 K hotter than surrounding areas at 9.5 microns. This large contrast is probably due to variations in the distribution of the ammonia clouds in the upper atmosphere.

Terrile, R. J.↗
NASA NTRS1977

Measures of Jupiter photographs - 1974/75 apparition

The 1974/75 Jupiter apparition is described. Photographic images have been measured and zonal velocities are given for all spots observed on four or more dates. Global and localized zonal flow patterns are graphically presented. Methane absorption band imagery at 890 nm indicates that white ovals and red spots are high in altitude, and blue features are cloud-free areas. The motions of blue features are complex and unlike the motions of other features. Interactions or associations between spots at five adjacent atmospheric currents have been observed. Zonal motion within an equatorial plume has been observed. Evidence is presented for a probable source of red spots in the North Tropical Zone.

Minton, R. B.↗
NASA NTRS1977

The distribution of ammonia and its photochemical products on Jupiter

Altitude profiles of ammonia and its photochemical products are generated in the light of measurements of the Jovian temperature structure, eddy transport coefficient, improved chemical scheme, and rate constants. Realistic limits are placed on the concentration of hydrazine which may participate in the recycling of ammonia on Jupiter. The maximum hydrazine-ice production rate is calculated to be about 1.3 mg/sq m per Jovian day. The distribution of nitrogen gas is presented with and without supersaturation of hydrazine. The nitrogen mixing ratio near the ammonia cloud top is estimated to be in the range between 10 to the -9th and 10 to the -11th power. An appreciable latitudinal variation in the ammonia concentration is expected.

Atreya, S. K.↗
NASA NTRS1976

Jupiter's distant environment

Qualitative features of the distant Jovian magnetosphere which have been noted previously are reviewed. These features include the highly deformable or spongy nature of the outer regions, the temporal variability of the middle magnetosphere, the presence of a near-equatorial ring current sheet from about 30 Jupiter radii to the magnetopause and the regular oscillation of particle and field properties associated with planetary rotation. We next add evidence for the persistent presence of a layer of magnetic turbulence in the portion of the magnetosphere just inside the magnetopause and we examine its properties. The importance of the presence of the turbulent layer to theoretical models of the magnetosphere is stressed.

Kivelson, M. G.↗
NASA NTRS1977

Soft electrons as a possible heat source for Jupiter's thermosphere

The 850 K exospheric temperature inferred for Jupiter from the radio-occultation experiments on Pioneers 10 and 11 is shown to imply a heat input of 0.25-0.5 erg/sq cm/sec. One possible source of this energy is precipitation of electrons from a warm plasma (temperature corresponding to energies of the order of 30-500 eV). A mechanism is suggested wherein the presence of this plasma can be accounted for by centrifugal acceleration and adiabatic compression of ionospheric electrons and protons. Present ideas of the source strength of ionospheric plasma, however, give heating rates that are too small by one to two orders of magnitude, although inferences from direct plasma measurements suggest that the required plasma is indeed present.

Hunten, D. M.↗
NASA NTRS1977

Impulsive penetration of filamentary plasma elements into the magnetospheres of the earth and Jupiter

Assuming that the solar wind plasma is usually nonuniform over distances of 10,000 km or less, it is shown that filamentary plasma elements stretched out from the sun can penetrate impulsively and become engulfed into the magnetosphere. The diamagnetic effects associated with these plasma inhomogeneities are observed in outer magnetospheres and magnetosheaths as dips or directional discontinuities in the magnetic field measurements. From the mean penetration distances of these diamagnetic plasma elements one can deduce a mean deceleration time, as well as an approximate value of the integrated Pedersen conductivity in the polar cusp of the earth and Jupiter.

Lemaire, J.↗
NASA NTRS1977

A determination of the L dependence of the radial diffusion coefficient for protons in Jupiter's inner magnetosphere

In a previous paper (Thomsen et al., 1977), a technique was proposed for estimating the radial diffusion coefficient (n) in the inner magnetosphere of Jupiter from the observations of the sweeping effect of the inner Jovian satellites on the fluxes of the energetic charged particles. The present paper extends this technique to permit the unique identification of the parameters D sub O and n, where the diffusion coefficient is assumed to be of the form D = D sub O L to the nth. The derived value of D sub O depends directly on assumptions regarding the nature and efficiency of the loss mechanism operating on the particles, while the value of n depends only on the assumed width of the loss region. The extended technique is applied to the University of Iowa Pioneer 11 proton data, leading to values of n of about O and D(6) of about 3 x 10 to the -8th (R sub J)-squared/sec, when satellite sweepup losses are assumed to be the only loss operating on the protons. The small value of n is strong evidence that the radial diffusion is driven by ionospheric winds.

Thomsen, M. F.↗
NASA NTRS1977

The effects of the atmospheric point-spread 'seeing' function on spatially resolved spectra of Jupiter

We present the results of an analysis of the effects of atmospheric seeing and of instrumental spectral and spatial resolution on the observed variation of absorption-line profiles across the disk of Jupiter. The technique described may be applied equally well to the analysis of observations of any extended astronomical source. These results show the necessity of obtaining accurate point-spread-function information during the course of observations of this nature. We also point out that in order to avoid the uncertainties and ambiguities inherent in attempts at deconvolution of observational data, one must properly convolve the appropriate spatial and spectral resolution functions with the models being tested and then compare the results with the observational data.

Gelfand, J.↗
NASA NTRS1977

Active spacecraft potential control system selection for the Jupiter orbiter with probe mission

It is shown that the high flux of energetic plasma electrons and the reduced photoemission rate in the Jovian environment can result in the spacecraft developing a large negative potential. The effects of the electric fields produced by this charging phenomenon are discussed in terms of spacecraft integrity as well as charged particle and fields measurements. The primary area of concern is shown to be the interaction of the electric fields with the measuring devices on the spacecraft. The need for controlling the potential of the spacecraft is identified, and a system capable of active control of the spacecraft potential in the Jupiter environment is proposed. The desirability of using this system to vary the spacecraft potential relative to the ambient plasma potential is also discussed. Various charged particle release devices are identified as potential candidates for use with the spacecraft potential control system. These devices are evaluated and compared on the basis of system mass, power consumption, and system complexity and reliability.

Beattie, J. R.↗