Jupiter's outer atmosphere

The current state of the theory of Jupiter's outer atmosphere is briefly reviewed. The similarities and dissimilarities between the terrestrial and Jovian upper atmospheres are discussed, including the interaction of the solar wind with the planetary magnetic fields. Estimates of Jovian parameters are given, including magnetosphere and auroral zone sizes, ionospheric conductivity, energy inputs, and solar wind parameters at Jupiter. The influence of the large centrifugal force on the cold plasma distribution is considered. The Jovian Van Alien belt is attributed to solar wind particles diffused in towards the planet by dynamo electric fields from ionospheric neutral winds and consequences of this theory are given.     

Jupiter's radiation belts

A model for the production and loss of energetic electrons in Jupiter's radiation belt is presented. It is postulated that the electrons originate in the solar wind and are diffused in toward the planet by perturbations which violate the particles' third adiabatic invariant. At large distances, magnetic perturbations, electric fields associated with magnotospheric convection, or interchange instabilities driven by thermal plasma gradients may drive the diffusion. Inside about 10 R_J the diffusion is probably driven by electric fields associated with the upper atmosphere dynamo which is driven by neutral winds in the ionosphere. The diurnal component of the dynamo wind fields produces a dawn-dusk asymmetry in the decimetric radiation from the electrons in the belts, and the lack of obvious measured asymmetries in the decimetric radiation measurements provides estimates of upper limits for these Jovian ionospheric neutral winds. The average diurnal winds are less than or comparable to those on earth, but only modest fluctuating winds are required to drive the energetic electron diffusion referred to above.The winds required to diffuse the energetic particles across the orbit of the satellite lo in a time equal to their drift period are also estimated. If Io is non-conducting, modest winds are required, but if Io is conducting, only small winds are needed. It is concluded that both protons and electrons are diffused in from the solar wind to small distances without serious losses occurring due to the particles being swept up by the satellites.Consideration of proton and electron diffusion in energy shows that once the electrons become relativistic, the ratio of proton to electron energy increases. Thus, if protons and electrons have the same energy in the solar wind, when the electrons reach nMeV, the protons will be nMeV if n ? 1 or n² MeV if n ? 1. If the proton-to-electron energy ratio is initially, e.g., 5, then these figures are 5n and 5n², respectively.     

Acetylene photopolymers in Jupiter's stratosphere

Laboratory data on the rate of photolytic polymerization of acetylene, highly diluted with hydrogen, at the pressure range of the Jovian stratosphere is presented. It is shown that this rate is sufficient to maintain the stratospheric aerosol haze which was observed on Jupiter by Smith et al. (1977, Icarus30).     

Mutual phenomena of Jupiter's satellites

Observations of an occultation of Europa by Io are fitted by a model light curve. The model has five free parameters, namely the radius of Europa, the impact parameter, the brightness ratio of the satellites, the time of midevent and the mean relative velocity. The model assumes a fixed value for the radius of Io and for the solar phase angle α, and that Europa has a uniform surface brightness. The OC residuals of the best fitting light curve are very small (～0.002 mag) and of a purely random nature; there is no evidence of albedo features. Taking α = 0 does not affect significantly the quality of the fit. Six mutual eclipses were also observed, and their times of minima agree well with the predictions of Aksnes Icarus21 (1974). For two events these predictions differ by about 20 min from those of Brinkmann and Millis Sky & Telescope45 (1973).     

Baroclinic instabilities in Jupiter's zonal flow

The baroclinic stability of Jupiter's zonal flow is investigated using a model consisting of two continuously stratified fluid layers. The upper layer, containing a zonal shear flow and representing the Jovian cloudy regions above p ～ 5 bars, is the same as Eady's (1949) model for the Earth. The lower layer has a relatively large but finite depth with a quiescent basic state, representing the deep Jovian fluid bulk below p ～ 5 bars. Due to the presence of the lower layer, the linearized non-dimensional growth rates are drastically reduced from the O(1) growth rates of the original Early model. Only very long wavelengths relative to the upper fluid's radius of deformation L₁ are unstable. Eddy transports of heat are also reduced relative to estimates based on scaling arguments alone. Since the hydrostatic approximation for the lower-layer perturbation breaks down at great depths, a second model is presented in which energy propagates downward in an infinitely deep lower fluid obeying the full linearized fluid equations. In this model, the growth rates are again very small, but now all wavelengths are unstable with maximum growth rates occurring for wavelengths O(1) relative to L₁. These results illustrate the importance for the upper-layer meteorology of the interface boundary condition with the lower fluid, which is radically different from the rigid lower boundary of the Earth's troposphere.     

Frost spectra: Comparison with Jupiter's Satellites

The near infrared spectral reflectance of pure CH₄, CO₂, H₂O, H₂S, NH₃ and NH₄SH frosts has been measured. Comparison with recent Galilean satellite spectra indicates that H₂O at approximately 150°K and with about 0.01 cm grain size is the major component on the surface of JII (Europa) and JIII (Ganymede); upper limits for the remaining frosts range from 5 to 28%. Materials other than these frosts must be present on the surface of JI (Io) and JIV (Callisto).     

Vertical cloud structure of Jupiter's Equitorial Plumes

A model for the vertical cloud structure of Jupiter's Equitorial Plumes is deduced based on an analysis of Voyager images of the equitorial region in the 6190Å methane band and the 6000-Å continuum, and ground-based 8900-Å methane band images of Jupiter. A computer code that represents scattering and absorption from aerosol and gas layers was applied to a heirarchy of increasingly complex model aerosol structures to match the observations in the three wavelengths. The observations are consistent with a model for the vertical cloud structure of the equitorial region that consists of four aerosol layers. A high-altitude haze layer (HAL) with optical depth τ = 1 uniformly blankets the equitorial region at an altitude between 100 and 250 mbar. Below that, a middle-level cloud layer between 400 and 800 mbar contains the well-known Equatorial Plumes. The Plume clouds are optically thick (τ ≥ 12), bright clouds with single scattering albedo $\text{ω}\text{= 0.997}$. They are probably composed of ammonia ice. The darker ($\text{ω}\text{= 0.990}$) interplume regions contain optically thinner clouds (2 ≤ τ ≤ 5) at the same altitude as the Plumes. An opaque cloud deck between 4000 and 6000 mbar, which is probably composed of water, forms the lowest model layer. In addition to these three layers, a thin forward scattering haze layer above 100 mbar was included in the models for consistency with previous work (Tomasko et al., 1978). We conclude that the vertical structure of the Equatorial Plume clouds is consistent with the hypothesis (Hunt et al., 1981) that the Plumes are caused by upwelling at the ammonia condensation level produced by bouyancy due to latent heat release from the condensation of water clouds nearly three scale heights below the Plumes.     

Decametric radio measurement of Jupiter's rotation period

A total of 26 measurements of Jupiter's 12-year average rotation period were made at frequencies of 18, 20, and 22.2 MHz at observatories in Florida and Chile. An improved method was employed in which histograms of occurrence probability vs central meridian longitude obtained at the same frequency and observatory during apparitions about 12 years (one Jovian year) apart were cross correlated. The longitude shift giving maximum cross correlation was used to correct the initially assumed rotation period value. The mean of the measurements is 9 hr 55 min 29.689 sec, with a standard deviation of the mean of 0.005 sec. This is about 0.02 sec, or 4 standard deviations, less than the System III (1965) value. The measurements indicate that the rotation period was not changing (linearly) at a rate in excess of 0.03 sec/yr. If the synoptic monitoring program is continued through the next maximum of the jovicentric declination of the Earth (D_E), we will probably be able to detect a rate of change in rotation period as small as 0.002 sec/yr. This accuracy might be sufficient to reveal a secular drift in Jupiter's magnetic field.     

Formation and photochemistry of Methylamine in Jupiter's atmosphere

The formation of methylamine (CH₃NH₂) in the upper troposphere and lower stratosphere of Jupiter is investigated. Translationally hot hydrogen atoms are produced in the photolysis of ammonia, phosphine, and acetylene which react with methane to produce methyl (CH₃) radicals; the latter recombine with NH₂ to form CH₃NH₂. Also, methane is catalytically dissociated to CH₃ + H by the species C₂ and C₂H produced in the photolysis of acetylene. It is shown that the combined production of CH₃NH₂ and subsequent photolysis to HCN is unlikely to account for the HCN observed near Jupiter's tropopause. Recombination of NH₂ and C₂H₅N followed by photolysis to HCN is the preferred path. Production of C₂H₆ by these two processes is negligible in comparison to the downward flux of C₂H₆ from the Lyman α photolysis region of CH₄. An upper limit column density on CH₃PH₂ is estimated to be ～10¹³ cm^?2 as compared to 10¹⁵ cm^?2 for CH₃NH₂. Hot H atoms account for a negligible fraction of the total ortho-para conversion by the reaction H + H₂     

The ammonia mixing ratio in Jupiter's stratosphere

Model calculations show that the far-infrared bands of ammonia are very sensitive to the ammonia distribution above the Jovian atmospheric inversion layer. Observation of the J = 5 and J = 6 ammonia bands at moderate resolution (R ～ 700) can differentiate between a cold trap model or the irreversible uv photodestruction model for the ammonia distribution. The amount of core emission is very sensitive to the distribution of ammonia above the Jovian inversion layer.     

Io's interaction with the magnetosphere

Jupiter's innermost Galilean satellite Io is regarded as a fairly good conductor ($\text{σ > 10}{}^{\mathrm{?5}}\text{Ω}{}^{\mathrm{?1}}\text{m}{}^{\mathrm{?1}}$). The trapping of magnetic field lines by Io and their deformation is described. A neutral point forms in the vicinity of the satellite. The magnetic field annihilation in the neutral point is enhanced by the emission of low frequency hmd waves. The power carried away by these waves may be as high 10¹⁵ W. The characteristic frequency of the wave and its variation while Io orbits around Jupiter is determined.     

The microwave spectrum of ammonia in Jupiter's atmosphere

High-frequency-resolution observations of the microwave inversions lines of ammonia in Jupiter have been compared with the models of the temperature inversion in the stratosphere of the planet to deduce that much of the ammonia must be frozen out in the cloud layer, leaving a smaller mixing ration above.     

On the presumed capture origin of Jupiter's outer satellites

The problem of the origin of Jupiter's outer satellites is treated within the framework of the theory of capture through collinear libration points. Lower bounds for the satellites' semimajor axes are found from a corrected rederivation of Bailey's capture theory. Upper bounds are found from a new derivation of the stability limit for satellites, based on Floquet stability theory.It is shown that if the bodies had near-zero relative velocity when passing the libration point, direct orbits would lie outside retrograde orbits, which is not the case for Jupiter. It is found that the dimensions and distributions of the direct group are well explained by libration-point capture with $\text{Jupiter's mass}\text{=}\text{1}\text{1730}$ solar mass, which is interpreted as indicating capture soon after Jupiter's formation. But ad hoc assumptions are required for this capture model to explain the retrograde group. It is concluded that the direct and retrograde groups may have had different mechanisms of origin.     

Mutual phenomena of Jupiter's five inner satellites in 1979

In this paper, we first predict eclipses and occultations of the Galilean satellites in 1979 and find that, although circumstances are generally poor, about 75 events are observable. We have then made a special point of including 40 eclipses of J5 (Amalthea) by the Galilean satellites in the hope that both visual and far-infrared light curves can be obtained—the former giving accurate astrometric information for J5, and the latter possibly bearing on its surface stucture or composition.     

Mutual phenomena of Jupiter's Galilean satellites 1973–74

Two series of predictions have been published for the 1973–1974 mutual phenomena of Jupiter's satellites, one (June–October, 1973) by Milbourn and Carey, and the other (February 1973–May 1974) by Brinkmann and Millis. The main purpose of this paper is to investigate some significant discrepancies between these two sets of predictions. New predictions are calculated for the period June 1973–May 1974. They agree very nearly with the predictions by Milbourn and Carey, but frequently differ by several minutes (up to 30 min when Jupiter III and IV are involved) from those by Brinkmann and Millis. Unlike the previous predictions, the new ones also give the estimated light decreases during the phenomena. The method of prediction is documented for future applications to Jupiter's and Saturn's satellites. The paper concludes with a brief discussion of the problems involved in extracting information about the positions, radii, and albedos of the satellites from observed light curves.     

Some particularities affecting the movements of Jupiter's red spot

The fluctuations in longitude of Jupiter's Red Spot are discussed. The long term fluctuations show behaviour similar to the fluctuations of zonal circulations on the Earth from 1830–1950. The three-monthly fluctuations have a temporal connection with the inferior conjunction of Mercury 1963–1971. Solar activity may be the key to both phenomena.     

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 cm^?2s^?1. 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 1–2 orders of magnitude, although inferences from direct plasma measurements suggest that the required plasma is indeed present.     

Alfvén drag for satellites orbiting in Jupiter's plasmasphere

According to a mechanism discovered by S. D. Drell, H. M. Foley, and M. A. Ruderman ((1965). J. Geophys. Res.70, 3131–3145), a satellite orbiting around a planet having a strong magnetic field and a dense ionospheric plasma dissipates orbital energy via radiation of Alfvén waves. The dissipation process is effective for objects larger than a minimum size and made of material exceeding a minimum electrical conductivity. It is shown that the corresponding drag effect could have influenced in a significant way the orbital evolution of the small natural moons orbiting inside or in proximity of Jupiter's ring. In particular this mechanism could explain the absence in the ring of objects in the size range from ～0.1 to ～10 km.     

Circular polarization of the 1.4 GHz emission from Jupiter's radiation belts

Measurements of the 1.4 GHz emission from Jupiter made when D_E was 3°·1 show the circular polarization to vary from +0.8 to ?1.1% as the planet rotates. The rms scatter of the points about the mean curve is only 0.09%. Expressed as a function of Jovian magnetic latitude the polarization at first increases linearly but beyond latitudes ～7° the curve flattens. This shape requires that the radiating electrons have a pitch angle distribution similar to that inferred earlier from the beaming and linear polarization. The magnitude of the circular polarization requires an equatorial magnetic flux density in the belt of about 0.3G, consistent with the Pioneer results.Compared with measurements made one orbital period earlier, the total flux density has decreased by 15%, but the beaming has not changed appreciably.     

On solar wind interaction with the earth's magnetosphere

Hydrodynamic and electrodynamic problems of solar wind interaction with the Earth's magnetosphere on the day-side are investigated.The initial fact, well established, is that the density of the magnetic field energy in the solar wind is rather small. Magnetic field intensity and orientation are shown to determine the character of the solar wind flow around the magnetosphere. For mean parameters of the wind, if the tangential component of the magnetic field is more or equal 5γ, the flow in the magneto-sheath will be laminar. For other cases the flow is of a turbulent type.For turbulent flow, typical plasma parameters are estimated: mean free path, internal scale of inhomogeneities and dissipated energy. The results obtained are compared with experimental data.For the case of laminar flow, special attention is paid to the situation when magnetic fields of the solar wind and Earth are antiparallel. It is suggested, on the basis of solid arguments, that the southward interplanetary field diffuses from the magnetosheath into the Earth's magnetosphere. These ideas are used for the estimation of the distance to the magnetopause subsolar point. A detailed comparison with results of observation is made. The coincidence is satisfactory. Theoretical investigation has been made to a great extent for thin magnetopause with thickness δ ～ R_He-gyroradius of an electron.It is shown that during magnetospheric substorms relaxation oscillations with the period τ = 100–300 sec must appear. A theorem is proved about the appearance of a westward electrical field during the substorm development, when the magnetosphere's day-side boundary moves Earthward and about the recovery phase, when the magnetopause motion is away from the Earth, when there is an eastward electrical field.In the Appendix, plasma wave exitation in the magnetopause is considered and conductivity magnitudes are calculated, including the reduction due to the scattering by plasma turbulence.