共查询到20条相似文献，搜索用时 31 毫秒
1.
The intensity of Jupiter's He 584 Å airglow has been measured by the Voyager U.V. spectrometers. The disc-averaged brightness is about 4 Rs and limb darkening is present. The intensity probably varies with longitude, the variation being out of phase with the H Lyman-α intensity bulge. Modelling of resonance scattering of the solar He 584 Å line by Jupiter's atmosphere has shown that the hydrogen and helium emissions can be explained about equally well by at least two self-consistent scenarios involving the structure (temperature and eddy diffusion coefficient) and excitation of the atmosphere. All our evidence points to a dramatic change of conditions in the Jovian atmosphere in the time between Pioneer and Voyager encounters. 相似文献
2.
Radio observations of Jupiter have been carried out at Goldstone, CA at a wavelength of 13 cm during the oppositions of 1969 and 1971. In 1969, circular-polarization and total-flux measurements were made with a 64-m radio telescope. From May through October 1971, Jupiter's flux density was measured at weekly intervals with a 26-m antenna. Analysis of the 2 years of data has yielded the following results: (a) The upper limit to the degree of circular polarization over the longitude ranges 10–100° and 160–250° System III (1957.0) is 1%; (b) the flux data have been used to derive a magnetospheric rotation period which is approximately 0.37s longer than the IAU System III (1957.0); (c) the flux-density data define beaming curves which are apparently different from 11-cm beaming curves measured in 1964; (d) Jupiter's peak flux density decreased by ～20% between 1964 and 1971, and 8% between 1969 and 1971. 相似文献
3.
C.K. Goertz 《Planetary and Space Science》1974,22(11):1491-1500
Decametric radiation from Jupiter impinging on the Earth's ionosphere is not in a magnetoionic base mode. If one assumes, as most researchers in the field do, that the radiation is generated at Jupiter in the extraordinary base mode, one must conclude that coupling has occurred somewhere near Jupiter. It is shown here that coupling does not occur in Jupiter's ionosphere but further out in the Jovian magnetosphere. The lack of observed Faraday rotation within Jupiter's ionosphere and magnetosphere cannot be used to rule ou ta hot, dense ionosphere and magnetosphere as was suggested previously. It is also shown that the radiation emerging from Jupiter should be elliptically polarized with an axial ratio varying between 0.4 and 0.9. The orientation of the polarization ellipse varies as a function of emitting longitude. 相似文献
4.
High-altitude spectra of Jupiter obtained from the Kuiper Airborne Observatory are analyzed for the presence of germane (GeH4) in Jupiter's atmosphere. Comparison with laboratory spectra shows that the strong Q branch of the ν3 band of germane at 2111 cm?1 is prominent in the Jovian spectra. The abundance of germane in Jupiter's atmosphere is 0.006 (±0.003) cm-am corresponding to a mixing ratio of 0.6 ppb. This trace amount of germane is consistent with chemical equilibrium calculations if the germane present at ～1000°K is carried up by convection to the spectroscopically observable region at ～300°K. 相似文献
5.
A.J. Dessler 《Icarus》1980,44(2):291-295
Theoretical arguments have been presented to the effect that both plasma and energy are supplied to the Jovian magnetosphere primarily from internal sources. If we assume that Io is the source of plasma for the Jovian magnetosphere and that outward flow of plasma from the torus is the means of drawing from the kinetic energy of rotation of Jupiter to drive magnetospheric phenomena, we can obtain a new, independent estimate of the rate of mass injection from Io into the Io plasma torus. We explicitly assume the solar wind supplies neither plasma nor energy to the Jovian magnetosphere in significant amounts. The power expended by the Jovian magnetosphere is supplied by torus plasma falling outward through the corotational-centrifugal-potential field. A lower limit to the rate of mass injection into the torus, which on the average must equal the rate of mass loss from the torus, is therefore derivable if we adopt a value for the power expended to drive the various magnetospheric phenomena. This method yields an injection rate of at least 103 kg/sec, a value in agreement with the results obtained by two other independent methods of estimating mass injection rate. If this injection rate from Io and extraction of energy from Jupiter's kinetic energy of rotation has been maintained over geologic time, then approximately 0.1% of Io's mass (principally in the form of sulfur and oxygen) has been lost to the Jovian magnetosphere, and Jupiter's spin rate has been reduced by less than 0.1%. 相似文献
6.
D.F. Strobel 《Planetary and Space Science》1982,30(8):839-848
The chemistry and evolution of Titan's atmosphere is reviewed in the light of the scientific findings from the Voyager mission. It is argued that the present N2 atmosphere may be Titan's initial atmosphere rather than photochemically derived from an original NH3 atmosphere. The escape rate of hydrogen from Titan is controlled by photochemical production from hydrocarbons. CH4 is irreversibly converted to less hydrogen rich hydrocarbons, which over geologic time accumulate on the surface to a layer thickness of ～0.5 km. Magnetospheric electrons interacting with Titan's exosphere may dissociate enough N2 into hot, escaping N atoms to remove ～0.2 of Titan's present atmosphere over geologic time. The energy dissipation of magnetospheric electrons exceeds solar e.u.v. energy deposition in Titan's atmosphere by an order of magnitude and is the principal driver of nitrogen photochemistry. The environmental conditions in Titan's upper atmosphere are favorable to building up complex molecules, particularly in the north polar cap region. 相似文献
7.
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 (DE), 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. 相似文献
8.
N.M. Brice 《Planetary and Space Science》1973,21(9):1587-1591
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. 相似文献
9.
Ammonia photolysis under simulated Jovian conditions indicates that the photochemical reaction would rapidly convert all the ammonia of Jupiter to nitrogen even in a large excess of hydrogen. It is suggested that ammonia is observed because the planet's atmosphere is deep and hot and/or because electrical discharge phenomena are important. 相似文献
10.
The Voyager Ultraviolet Spectrometer has made extensive observations of airglow from Jupiter's dark-side equatorial latitudes. The brightness of H Lyman α (Lyα), the only emission detected, varies between 700 and 1000 rayleighs (R) as a function of lungitude. The dark side of Jupiter is illuminated by sky background Lyα arising from resonance scattering of the solar Lyα 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 Lyα emission. The additional Lyα 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 Lyα measurements, the exciting particles are thought to have a soft energy spectrum and deposit about 0.04 erg cm?2 sec?1 in the atmosphere. There is evidence for an asymmetrical precipitation pattern associated with the longitudinal variation in Ly α emission, and a suggestion of a strong day-night difference in precipitation as well. 相似文献
11.
P. A. Cloutier R. E. Daniell Jr. A. J. Dessler T. W. Hill 《Astrophysics and Space Science》1978,55(1):93-112
The ionosphere of Jupiter's satellite Io, discovered by the Pioneer 10 radio-occultation experiment, cannot easily be understood in terms of a model of a gravitationally bound, Earth-like ionosphere. Io's gravitational field is so weak that a gravitationally bound ionosphere would probably be blown away by the ram force of the Jovian magnetospheric wind — i.e., the plasma corotating in the Jovian magnetosphere. We propose here a model in which the material for Io's atmosphere and ionosphere is drawn from the ionosphere of Jupiter through a Birkeland current system that is driven by the potential induced across Io by the Jovian corotation electric field. We argue that the ionization near Io is caused by a comet-like interaction between the corotating plasma and Io's atmosphere. The initial interaction employs the critical velocity phenomenon proposed many years ago by Alfvén. Further ionization is produced by the impact of Jovian trapped energetic electrons, and the ionization thus created is swept out ahead of Io in its orbit. Thus, we suggest that what has been reported as a day-night ionospheric asymmetry is in fact an upstream-downstream asymmetry caused by the Jovian magnetospheric wind.Paper dedicated to Professor Hannes Alfvén on the occasion of his 70th birthday, 30th May, 1978. 相似文献
12.
The theory of formation of pressure-broadened methane lines and collision-narrowed hydrogen quadrupole lines in a Jovian atmosphere is studied in detail for a physically realistic model of the planet's lower atmosphere. Only observations of the center-to-limb (CTL) variations of the equivalent width of absorption lines for both of these molecules can identify the structure of the visible cloud layers. Observations of the CTL variation of methane and hydrogen quadrupole lines are the most suitable for studying the Jovian atmosphere. The CTL variations for hydrogen are much greater and more sensitive to variations of the properties of the thin upper tropospheric cloud layer than the corresponding observations of methane lines. A detailed comparison of hydrogen quadrupole with methane lines is made for the same continuum conditions, enabling us to develop a detailed understanding of the formation of the collision-narrowed hydrogen quadrupole lines in a Jovian atmosphere. 相似文献
13.
If Jupiter's and Saturn's fluid interiors were inviscid and adiabatic, any steady zonal motion would take the form of differentially rotating cylinders concentric about the planetary axis of rotation. B. A. Smith et al. [Science215, 504–537 (1982)] showed that Saturn's observed zonal wind profile extends a significant distance below cloud base. Further extension into the interior occurs if the values of the eddy viscosity and superadiabaticity are small. We estimate these values using a scaling analysis of deep convection in the presence of differential rotation. The differential rotation inhibits the convection and reduces the effective eddy viscosity. Viscous dissipation of zonal mean kinetic energy is then within the bounds set by the internal heat source. The differential rotation increases the superadiabaticity, but not so much as to eliminate the cylindrical structure of the flow. Very large departures from adiabaticity, necessary for decoupling the atmosphere and interior, do not occur. Using our scaling analysis we develop the anelastic equations that describe motions in Jupiter's and Saturn's interiors. A simple problem is solved, that of an adiabatic fluid with a steady zonal wind varying as a function of cylindrical radius. Low zonal wavenumber perturbations are two dimensional (independent of the axial coordinate) and obey a modified barotropic stability equation. The parameter analogous to β is negative and is three to four times larger than the β for thin atmospheres. Jupiter's and Saturn's observed zonal wind profiles are close to marginal stability according to this deep sphere criterion, but are several times supercritical according to the thin atmosphere criterion. 相似文献
14.
V. I. Shematovich 《Solar System Research》2006,40(3):175-190
This paper analyzes the formation, kinetics, and transport of hot oxygen atoms in the atmosphere of the Jovian satellite Europa. Atmospheric sources of suprathermal oxygen atoms are assumed to be represented by the processes of dissociation of molecular oxygen, which is the main component of the atmosphere, by solar UV radiation and electron fluxes from the inner magnetosphere of Jupiter, as well as by the reaction of dissociative recombination of the main ionospheric ion O 2 + which thermal electrons. It is shown that dissociation in Europa’s near-surface atmosphere is balanced by the processes of the loss of atomic oxygen due to the effective escape of suprathermal oxygen atoms into the inner magnetosphere of Jupiter along the orbit of Europa and due to ionization by magnetospheric electrons and catalytic recombination of oxygen atoms on the icy surface of the satellite. It thus follows that atomic oxygen is only a small admixture to the main atmospheric component—molecular oxygen—in the near-surface part of the atmosphere. However, the outer exospheric layers of Europa’s atmosphere are populated mostly by suprathermal oxygen atoms. The near-surface molecular envelope of Europa is therefore surrounded by a tenuous extended corona of hot atomic oxygen. 相似文献
15.
L. Trafton 《Icarus》1980,41(2):318-325
The hot Jovian plasma torus discovered by Voyager 1 is responsible for the periodic intensity variations of Io's sodium cloud, which are correlated with Io's magnetic latitude. The plasma torus must be a long-lived phenomenon in spite of its apparent absence at the time of the Pioneer flybys. The hot electrons (～105°K) must be concentrated ～1 RJ from the magnetic equator in order to produce the observed variations. Electron impact ionization in the hot plasma torus is strong enough to form and to maintain Io's ionosphere; the hot plasma torus may be the dominant agent forming the ionosphere. Io's bound atmosphere is dense enough that the plasma torus electrons cannot cause a noticeable variation in its Na emission intensity. 相似文献
16.
Models of convection in Jupiter's interior are studied to test the hypothesis that internal heat balances the absorbed sunlight at each latitude. Such a balance requires that the ratio of total emitted heat to absorbed sunlight be above a critical value 4/π ≈ 1.27. The necessary horizontal heat transport then takes place in the interior instead of in the atmosphere. Regions of stable stratification can arise in the interior owing to the effects of solar heating and rotation. In such regions, upward heat transfer takes place on sloping surfaces, as in the Earth's atmosphere, provided there are horizontal temperature gradients. Potential temperature gradients are found to be small, and the time constant for the pattern to reach equilibrium is found to be short compared to the age of the solar system. It is suggested that Jupiter and Saturn owe their axisymmetric appearance to internal heat flow, which eliminates differential heating in the atmosphere that would otherwise drive meridional motions. 相似文献
17.
The Galileo spacecraft explored Jupiter’s magnetotail in a low-inclination orbit, where it detected the signatures of tail reconnection. In this paper, we examine and classify the tail reconnection signatures into four types: dipolarizations, strong northward Bθ excursions, tailward-moving plasmoids and planetward-moving plasmoids. The distribution of these four types of events is used to infer the most probable location of the Jovian tail reconnection site to be near 0200 LT at a planetocentric distance of 80 Jovian radii. Dipolarizations are mainly observed planetward of this point, and strong northward Bθ excursions and plasmoids are found mostly tailward. The observations also suggest that the Jovian tail reconnection starts at a point (neutral point), a localized region in the tail, instead of along an extended azimuthal line (X-line). Using the updated Khurana’s Jupiter’s magnetospheric model, which includes the external field and the effects of the swept-back configuration of tail field lines, we map the signatures of Jovian tail reconnection into the Jupiter’s ionosphere. We confirm that the dawn auroral storms or the polar dawn spots observed by the Hubble Space Telescope (HST) are located close to the extrapolated footpoints of tail dipolarizations and could be the auroral signatures of tail reconnection. 相似文献
18.
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 RJ 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. 相似文献
19.
There is a current need for a redefinition of the Jovian System III longitude measure. We report on a proposed new definition which has been widely circulated among users and has met with general acceptance. Some errors in current calculations of System III [1957.0] are not noted so that these errors can be avoided in future calculations. 相似文献
20.
The Jovian satellites and ring are continuously bombarded by high-energy galacic cosmic rays and magnetospheric ions. Nuclear interactions will create very energetic neutrons and pions. The decay of some of these unstable particles within the Jovian magnetosphere wil result in trapped protons and ultrarelativistic electrons and positrons. Although this source is weak compared to those that yield lower-energy magnetospheric particles, it is expected to generate the most energetic Jovian particles. These processes are briefly described. 相似文献