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NASA NTRS1979

Phosphine absorption in the 5-micron window of Jupiter

Since the original suggestion by Gillett et al. (1969) it has generally been assumed that the region of partial transparency near 5 micron in Jupiter's atmosphere (the 5-micron window) is bounded by the nu sub 4 NH3 at 6.1 micron and the nu sub 3 CH4 band at 3.3 micron. New measurements of Jupiter and of laboratory phosphine (PH3) samples show that PH3 is a significant contributor to the continuum opacity in the window and in fact defines its short-wavelength limit. This has important implications for the use of 5-micron observations as a means to probe the deep atmospheric structure of Jupiter. The abundance of PH3 which results from a comparison of Jovian and laboratory spectra is about 3 to 5 cm-am. This is five to eight times less than that found by Larson et al. (1977) in the same spectral region, but is in good agreement with the result of Tokunaga et al. (1979) from 10-micron observations.

Beer, R.↗
NASA NTRS1979

Silicon compounds in the Jupiter atmosphere

The formation of colored silicon compounds under nonequilibrium conditions is discussed with reference to the composition of the Jupiter atmosphere. It is shown that many of these reactions produce strongly colored intermediates that are relatively stable and similar in appearance to those observed on Jupiter. It is suggested that the silicon compounds could substantially contribute to the colors observed on Jupiter. The colored intermediates may be the result of relatively rapid amorphous silicon monoxide formation in vertical atmospheric currents in the region near the red spot and in the red spot itself.

Howland, G.↗
NASA NTRS1980

Electromagnetic scattering lifetimes for dust in Jupiter's ring

The lifetime of the charged, micron-sized dust particles found to lie in a ring at 1.8 Jupiter radii from Jupiter against electromagnetic scattering is estimated. Interactions of the particles with the Jovian magnetic field dipole are found to spread particle orbits out to a much greater extent than observed for particle charges greater than -10 V, and to result in slightly eccentric, open orbits for the dust particles, with eccentricities dependent on particle size. In addition, fluctuations within the magnetic field are found to lead to significant changes in the eccentricity and inclination of the ring particle orbits. It is concluded that Jovian ring particles, if charged to -10 V as is consistent with Voyager data, will be strongly perturbed and scattered on a short time scale (100 yr), so the ring must be constantly replenished or it is a temporary phenomenon. Finally, the dust cloud observed to extend above, below, and beyond the Jupiter ring is attributed to the electromagnetic scattering of particles smaller than the ring particles.

Consolmagno, G. J.↗
NASA NTRS1980

The effect of dense cores on the structure and evolution of Jupiter and Saturn

The evolutionary and static models of Jupiter and Saturn were calculated with homogeneous solar composition mantles and dense cores of material consisting of solar abundances of SiO2, MgO, Fe, and Ni. Evolutionary sequences for Jupiter were calculated with cores of mass ranging from 2 to 8% of the Jovian mass; the Saturn sequences ranged from cores of mass of 16 to 22% of total mass. Two envelope mixtures representative of the solar abundances were used: they contained mass fraction of 0.74 and 0.77 of hydrogen, respectively, and 0.24 and 0.21 mass fractions of helium. For Jupiter, the observations of the temperature at 1 bar pressure, of radius and of internal luminosity were best fit by evolutionary models with a core mass of about 6.5% and chemical composition of 0.77 mass fraction of hydrogen and 0.21 mass fraction of helium. The cooling time calculated for Saturn was 2.6 x 10 to the 9th yr, almost a factor of 2 less than the percentage of the solar system.

Grossman, A. S.↗
NASA NTRS1980

Maximum frequency of the decametric radiation from Jupiter

The upper frequency limits of Jupiter's decametric radio emission are found to be essentially the same when observed from the earth or, with considerably higher sensitivity, from the Voyager spacecraft close to Jupiter. This suggests that the maximum frequency is a real cut-off corresponding to a maximum gyrofrequency of about 38-40 MHz at Jupiter. It no longer appears to be necessary to specify different cut-off frequencies for the Io and non-Io emission as the maximum frequencies are roughly the same in each case.

Barrow, C. H.↗
NASA NTRS1980

Airglow from Jupiter's nightside and crescent - Ultraviolet spectrometer observations from Voyager 2

The Voyager Ultraviolet Spectrometer has made extensive observations of airglow from Jupiter's dark-side equatorial latitudes. The brightness of H Lyman alpha, the only emission detected, varies between 700 and 1000 rayleighs (R) as a function of longitude. The dark side of Jupiter is illuminated by sky background Lyman alpha arising from resonance scattering of the solar Lyman alpha line by the neutral hydrogen of the interstellar medium. Calculations show that resonance scattering of this sky background by hydrogen in Jupiter's thermosphere will produce about 300 R of Lyman alpha emission. The additional Lyman alpha observed is probably excited by electrons and protons precipitating at equatorial latitudes. Based on the 500-R upper limit set here on the dark-side H2 Lyman and Werner bands, and the Lyman alpha measurements, the exciting particles are thought to have a soft energy spectrum and deposit about 0.04 erg/sq cm per sec in the atmosphere. There is evidence for an asymmetrical precipitation pattern associated with the longitudinal variation in Lyman alpha emission, and a suggestion of a strong day-night difference in precipitation as well.

Mcconnell, J. C.↗
NASA NTRS1981

Jupiter's magnetopause, bow shock, and 10-hour modulated magnetosheath Voyagers 1 and 2

This summary report discusses Jupiter's magnetopause, bow shock and magnetosheath, based on fine scale magnetic field data from the Voyager 1 and 2 encounters. Explicit models of the dawnside magnetopause and bow shock in Jupiter's orbital plane employ an axisymmetric parabola and hyperbola, respectively, and satisfy average boundary crossing positions, inbound and outbound; these models are determined separately for the two encounters. A new phenomenon has been discovered in Jupiter's magnetosheath. It is manifested as (5 or) 10 hour quasi-periodic modulation of the direction of the magnetic field in the outbound magnetosheath, predominantly in the northward (N) and southward (S) directions. It was seen to occur during both encounters and appears most evident in Voyager 2 outbound observations.

Lepping, R. P.↗
NASA NTRS1981

1979J3 - Discovery of a previously unknown satellite of Jupiter

During a detailed search of Voyager 1 frames for additional observations of the satellite 1979J1, two small dark spots were observed in transit in several consecutive wide-angle frames of the Jovian atmosphere. The size, spacing, and motion of these pairs of dark spots indicated that they were the images of 1979J1 and its shadow. Subsequent analysis of images spanning 6 days, however, proved that the satellite observed in these Voyager 1 frames would have been occulted by Jupiter at the times of the Voyager 2 images of 1979J1 and was, therefore, a new satellite. It was subsequently found in transit on Voyager 2 images within 13 deg of the Voyager 1 prediction. Its period is 7 hrs 4 min 30 sec + or - 3 sec, and its mean distance is 1.793 Jupiter radii (Jupiter radius = 71,400 km). The observable profile appears to be roughly circular with a diameter of 40 km, and the albedo is approximately 0.05, similar to Amalthea's.

Synnott, S. P.↗
NASA NTRS1981

Compression of Jupiter's magnetosphere by the solar wind - Reexamination via MHD simulation of evolving corotating interaction regions

Major changes in the solar wind before, during and after the Pioneer 10 and 11 missions' encounter with the Jovian magnetosphere are considered. A numerical simulation of the multiple corotating interaction region (CIR) evolutions from one spacecraft to its sister spacecraft is shown to have confirmed the suggestion by Smith et al (1978) that Jupiter's magnetosphere was compressed by interplanetary CIRs during three out of four of the observed events. The MHD simulation presented suggests that the Jupiter magnetosphere reacts to solar wind rarefactions by expanding. A pair of previously unexplained magnetopause crossings of the Pioneer 11 outbound pass may be due to a delayed reexpansion of the Jupiter magnetosphere from a compression that occurred during the inbound pass.

Smith, Z. K.↗
NASA NTRS1982

Thermal Structure of Jupiter and Saturn

Temperatures in the sensible regions of the atmospheres of the outer planets are quite cold. The temperature structures for Jupiter, Saturn, Uranus and Neptune, derived from the equilibrium models are presented in preparation. The vertical temperature profiles for Jupiter and Saturn, the molecular spectroscopic data which form the basis for this type of analysis, and the problems involved with these models for molecular absorption and with the recovery technique in general, are discussed. Results for Jupiter and Saturn from the Pioneer and Voyager infrared experiments are also presented.

Orton, G.↗
NASA NTRS1981

Models for Jupiter's decametric arcs

Arc-shaped structures that dominate Jupiter's decametric emission are discussed in terms of a magnetic fine structure. The sequence of arcs manifest the occurence of widespread fine structures similar to the white ovals on Jupiter's visible surface. An arc concave toward increasing time occurs at the east limb passage, and an arc convex occurs at the west limb passage, which is consistent with the early source producing vertex early arcs, and the late source producing vertex late arcs. Due to the geometry of the Io plasma torus (IPT) which is arranged so that Io skims the northern surface of the IPT, for any connection between Io and Jupiter's surface that involves Alfven waves, the propagation time, the refraction and the directional defocusing of these waves must be strongly influenced by the amount of Alfven wave path length between the instantaneous position of Io and the surface of the IPT.

Warwick, J. W.↗
NASA NTRS1981

Jupiter and Io - A binary magnetosphere

A qualitative assessment is presented of Voyager 1 and 2 data analysis and theoretical interpretation, regarding the Io torus and Jovian aurora, dominant magnetospheric components, plasma waves and radio emissions, with emphasis on the difficulty of accounting for either the Jupiter aurora or Io torus EUV emission luminosities in energetic terms. Jupiter's middle atmosphere is also considered, with attention to observations of corotating ions, their ambiguities and their implications. After a discussion of the question of Jupiter's interaction with the solar wind, as manifested by its magnetic tail, terrestrial magnetospherics are invoked in the construction of a tentative unification of observed phenomena which is within the latitude afforded by the current state of data reduction.

Scarf, F. L.↗
NASA NTRS1982

The far-ultraviolet spectra and geometric albedos of Jupiter and Saturn

Spectra and geometric albedoes in the range 1200 to 1940 A are compiled for Jupiter and Saturn on the basis of IUE observations. The spectra of both planets are dominated by H Lyman-alpha emission line at 1216 A, although absorption bands of C2H2 are apparent at longer wavelengths, particularly in the spectrum of Saturn, and the C I line at 1657 A is also observed. Geometric albedoes show emission features corresponding to the weak H2 Lyman and Werner bands around 1230-1280 A, auroral Lyman band emission, C I emission, and C2H2 absorption from 1600 to 1900 A. A model of atmospheric absorption in homogeneously mixed atmospheres of H2 and trace molecular absorbers is then presented and fit to the Jupiter albedo, resulting in a predicted atmosphere containing C2H2 and an unidentified molecular or particulate absorber. Finally, north-south maps of Jupiter continuum emission show limb darkening, and a comparison of equatorial and polar spectra indicates a polar increase in C2H2 absorption and weaker polar H2 emissions than previously reported.

Clarke, J. T.↗
NASA NTRS1982

Galileo probe forebody flowfield predictions during Jupiter entry

This paper presents forebody flowfield solutions for Jupiter entry conditions where the ablation injection rate is coupled with the surface heating rate. The calculations are made with a time-dependent viscous-shock-layer analysis where the flow is assumed to be in chemical equilibrium. The results obtained demonstrate how variations in various properties influence the calculations and how recent modifications in probe forebody heatshield design influence the heating and mass-loss conditions for Jupiter entry. The heatshield mass-loss rates are shown to decrease when the new radiative and thermodynamic property values are used as well as when the nose bluntness is reduced. Also, the inclusion of a finite surface reflectivity reduces the mass loss whereas spallation increases the mass loss by about 6 percent. Finally, the heating, mass-loss, and flowfield structure characteristics are described for a 335-kg probe as it enters the atmosphere of Jupiter.

Moss, J. N.↗
NASA NTRS1982

Magnetospheres of Jupiter and Saturn

During the time from 1973 to 1981, the giant planets, Jupiter and Saturn, have been studied with the aid of the spacecraft Pioneers 10, 11, and Voyagers 1 and 2. The present investigation is concerned with the study of the magnetospheres of these planets, taking into account the immediate region of their environment in which the planetary magnetic field is the dominant physical force, and the boundary of the magnetospheres which is formed by the interaction with the solar wind. Attention is given to the recent results obtained by the Voyagers. It is found that the basic features of the magnetospheres of Jupiter and Saturn are similar to those of the earth. There are, however, also differences with the earth which relate to the large amount of entrapped low energy plasmas that form a magnetodisk and an Io associated torus at Jupiter, while at Saturn there is a Titan torus and a substantial ring current.

Ness, N. F.↗
NASA NTRS1982

Interplanetary mission design handbook. Volume 1, part 3: Earth to Jupiter ballistic mission opportunities, 1985-2005

Graphical data necessary for the preliminary design of ballistic missions to Jupiter are provided. Contours of launch energy requirements, as well as many other launch and Jupiter arrival parameters, are presented in launch date/arrival date space for all launch opportunities from 1985 through 2005. In addition, an extensive text is included which explains mission design methods, from launch window development to Jupiter probe and orbiter arrival design, utilizing the graphical data in this volume as well as numerous equations relating various parameters.

Sergeyevsky, A. B.↗
NASA NTRS1982

Energetic-ion acceleration and transport in the upstream region of Jupiter: Voyager 1 and 2

Long-lived upstream energetic ion events at Jupiter appear to be very similar in nearly all respects to upstream ion events at Earth. A notable difference between the two planetary systems is the enhanced heavy ion compositional signature reported for the Jovian events. This compositional feature has suggested that ions escaping from the Jovian magnetosphere play an important role in forming upstream ion populations at Jupiter. In contrast, models of energetic upstream ions at Earth emphasize in situ acceleration of reflected solar wind ions within the upstream region itself. Using Voyager 1 and 2 energetic ( approximately 30 keV) ion measurements near the magnetopause, in the magnetosheath, and immediately upstream of the bow shock, the compositional patterns are examined together with typical energy spectra in each of these regions. A model involving upstream Fermi acceleration early in events and emphasizing energetic particle escape in the prenoon part of the Jovian magnetosphere late in events is presented to explain many of the features in the upstream region of Jupiter.

Baker, D. N.↗
NASA NTRS1983

The C-12/C-13 ratio in Jupiter from the Voyager infrared investigation

An analysis of the v(4) band of CH4 in the spectra recorded by the Voyager 1 IRIS experiment has yielded a C-12/C-13 ratio in Jupiter that is 160 plus 40 or minus 55, or 1.8 plus 0.4 or minus 0.6 times the terrestrial value. It is noted that while no plausible theory predicts such a difference between the C-12/C-13 ratio values of Jupiter and the inner solar system, values of this ratio in the solar neighborhood 4.5 million years ago, inferred from recent interstellar medium measurements, are compatible with the present determination in Jupiter. The Jovian, rather than the terrestrial value, would then be representative of the carbon isotope ratio in the primitive solar nebula.

Courtin, R.↗