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1.
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
2.
It is now recognized that a number of neutral-plasma interaction processes are of great importance in the formation of the Io torus. One effect not yet considered in detail is the charge exchange between fast torus ions and the atmospheric neutrals producing fast neutrals energetic enough to escape from Io. Since near Io the plasma flow is reduced, the neutrals of charge exchange origin are not energetic enough to leave the Jovian system; these neutrals are therefore distributed over an extensive region as indicated by the sodium cloud. It is estimated here that the total neutral injection rate can reach 1027 s?1 if not more. New ions subsequently created in the distributed neutral atomic cloud as a result of charge exchange or electron impact ionization are picked up by the corotating magnetic field. The pick-up ions are hot with initial gyration speed near the corotation speed. The radial current driven by the pickup process cannot close in the torus but must be connected to the planetary ionosphere by field-aligned currents. These field-aligned currents will flow away from the equator at the outer edge of the neutral cloud and towards it at the inner edge. We find that the Jovian ionospheric photoelectrons alone cannot supply the current flowing away from the equator, and torus ions accelerated by a parallel electric field could be involved. The parallel potential drop is estimated to be several kV which is large enough to push the torus ions into the Jovian atmosphere. This loss could explain the sharp discontinuous change of flux tube content and ion temperature at L = 5.6 as well as the generation of auroral type hiss there. Finally we show that the inner torus should be denser at system III longitudes near 240° as a result of the enhanced secondary electron flux in this region. This effect may be related to the longitudinal brightness variation observed in the SII optical emissions. 相似文献
3.
Thomas R. McDonough 《Icarus》1975,24(4):400-406
The Jovian hydrogen torus associated with Io, that was observed by Judge and Carlson, has been found by them to be a third of a torus rather than a complete torus. It is shown that the energetic particles observed by Pioneer 10 do not ionize atomic hydrogen sufficiently fast to erode the torus as observed. It is proposed that the reason an incomplete torus exists is the presence of a corotating cold magnetospheric plasma. If this explanation is correct, the angular extent of the fractional torus is a measure of the density of the magnetospheric plasma near Io's orbit, which is found to be ～102cm?3. It is shown that such a plasma may provide an adequate input to Io, where it can recombine and escape, to form enough hydrogen atoms to explain the number of observed torus atoms. Thus the magnetospheric plasma may serve as both the source and the sink of the torus. However, while it is not difficult to make the plasma be the sink of the toroidal hydrogen, it is difficult (although perhaps possible) to self-consistently make it the source. It may be necessary to invoke some other mechanism to generate the hydrogen. 相似文献
4.
The hydrogen bulge is a feature in Jupiter's upper atmosphere that co-rotates with the planetary magnetic field (i.e. the hydrogen bulge is fixed in System III coordinates). It is located approximately 180° removed in System III longitude from the active sector, which has been identified as the source region for Jovian decametric radio emission and for release of energetic electrons into interplanetary space. According to the magnetic-anomaly model, the active sector is produced by the effect of the large magnetic anomaly in Jupiter's northern hemisphere. On the basis of the magnetic-anomaly model, it has been theoretically expected for some time that a two-cell magnetospheric convection pattern exists within the Jovian magnetosphere. Because the convection pattern is established by magnetic-anomaly effects of the active sector, the pattern co-rotates with Jupiter. (This is in contrast to the Earth's two-cell convection pattern that is fixed relative to the Sun with the Earth rotating beneath it.) The sense of the convection is to bring hot magnetospheric plasma into the upper atmosphere in the longitude region of the hydrogen bulge. This hot plasma contains electrons with energies of the order of 100keV that dissociate atmospheric molecules to produce the atomic hydrogen that creates the observed longitudinal asymmetry in hydrogen Lyman alpha emission. We regard the existence of the hydrogen bulge as the best evidence available thus far for the reality of the expected co-rotating magnetospheric convection pattern. 相似文献
5.
Using Voyager results, we have made crude estimates of the rate at which Io loses volatiles by a variety of processes to the surrounding magnetosphere for both the current SO2-dominated atmosphere as well as hypothetical paleoatmospheres in which other gases, such as N2, may have been the dominant constituent. Loss rates are strongly influenced by the surface pressure on the night side, the relationship between the exobase and the Jovian magnetospheric boundary, the exospheric temperature, and the peak altitudes reached by volcanic plumes. Several mechanisms make significant contributions to the prodigious rate at which Io is currently losing volatiles. These include: interaction of the magnetospheric plasma with volcanic plume particles and the background atmosphere; sputtering of ices on the surface, if the nightside atmospheric pressure is low enough; and Jeans' escape of O, a dissociation product of SO2 gas. For paleoatmospheres, only the first two of these mechanisms would have been effective. However, they are capable of eliminating large amounts of N2 and other volatiles from Io over the satellite's lifetime. Io could have also lost large amounts of water over its lifetime due to the extensive recycling of water between its upper and lower crust, with the partial dissociation of water vapor in silicate magma chambers initiating this loss process. Significant amounts of water may also have been lost as a result of the interaction of the magnetospheric plasma with water ice particles in volcanic plumes. Once an SO2-dominated atmosphere becomes established, much water may have also been lost through the sputtering of surface water ice. 相似文献
6.
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
7.
An equation of heat transport in the Jovian magnetosphere is formulated and solved in the L range between 2 and 7. Sources of thermal energy include the heating associated with inward radial diffusion and a hypothetical heat supply originating from Io's dynamo action. The principal sink of the thermal energy is charge exchange in Io's hydrogen torus. In order to explain the density and temperature profile reported by Frank et al. (1976), the presence of the heat source at Io is essential and the density of the torus hydrogen has to be considerably lower than the value inferred from Lα observations by Carlson and Judge (1975). Radial diffusion represents the principal heating mechanism for plasma at very low L values. 相似文献
8.
Volcanic plumes on the Jovian satellite Io may be a visible manifestation of a plasma-arc discharge phenomenon. The amount of power in the plasma arc (1011 W) is not enough to account for all the energy dissipated by the volcanoes. However, once a volcano is initiated by tidal and geologic processes, the dynamics of the volcanic plumes can be influenced by the plasma arcs. As initially pointed out by Gold (1979), plasma arcs are expected because of 106 A currents and 400 kV potentials generated by the flow past Io of a torus of relatively dense magnetospheric plasma. We utilize our experience with laboratory plasma arcs to investigate the plume dynamics. The filamentation in the plume of the volcano Prometheus and its cross-sectional shape is quantitatively consistent with theories developed from laboratory observation.Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988. 相似文献
9.
The interaction of Io with the Jovian magnetosphere generates auroral and radio emissions. The underlying electron acceleration process is not understood and few observations exist to constrain the theoretical models. The source of energy for the electron acceleration is in all likelihood supplied from the Alfvén wings that stretch out from both poles of Io into the two Jovian hemispheres. The form of the current system associated with the Alfvén wings has been disputed, some suggesting that the greatly slowed flow near Io implies that a steady current loop links Io to Jupiter's ionosphere, others arguing that the return waves appear only downstream of Io and others suggesting that both forms develop. Given the finite inclination of the Alfvén wings implied by the finite value of the Alfvén Mach number and the strong reflection that occurs at the boundary of the Io torus, we argue that no steady current loop can be invoked between Io and Jupiter's ionosphere. However, the energetics of the auroral and radio emissions imply that most of the energy in the Alfvén wings is transformed into electron acceleration at high-latitudes, that is, outside the Io torus. The dilemma then is to understand how a large fraction of the power penetrates the reflecting boundary. We present data from Galileo's multiple flybys of Io that suggest that the coupling with the Jovian ionosphere is mediated by filamentary Alfvén wings associated with electromagnetic waves propagating out of the torus. In particular, we report on the systematic observation, within the cross-section of Io's Alfvén wings and in their immediate vicinity, of intense electromagnetic waves at frequencies up to several times the proton gyrofrequency. We interpret these “high-frequency/small-scale” waves as the signature of a strong filamentation/fragmentation of the Alfvén wings before they reflect off of the sharp boundary gradient of the Io torus. As a consequence, we suggest that most of the primary energy is converted into “high-frequency/small-scale” electromagnetic waves that can propagate out from the torus toward Jupiter's ionosphere. Reaching high-latitudes, these waves are able to accelerate electrons to almost relativistic speeds. 相似文献
10.
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
11.
《Planetary and Space Science》1999,47(3-4):521-527
It is widely recognized that Io, the innermost of the Galilean satellites, releases matter into the rapidly-rotating Jovian magnetosphere at rates that may be as high as a ton per second. Following ionization, this iogenic, heavy-ion plasma dominates the dynamics of the Jovian magnetosphere. On average this plasma must be lost at a rate that balances its generation but we do not know whether this process is steady or intermittent. Measurements by the Galileo magnetometer suggest that this process is unsteady. By estimating the magnetic and particle stresses from these observations, we further can derive a mass density profile that is consistent with earlier measurements of the current sheet density and that is consistent with estimates of the radial transport of mass in the middle Jovian magnetosphere. 相似文献
12.
The interaction of the Jovian energetic radiation belt electrons, and the Jovian plasma, with an ambient dust population is examined. Firstly the distribution of dust, ejected from Io, in the inner magnetosphere is calculated. Using the mass loss in submicron particles of ~13g/sec, which is required to model the intensity and shape of the Jovian ring in the model of Morfill etal. (1980b), it is possible to quantitatively calculate losses of magnetospheric ions and electrons due to direct collisions with charged dust particles as well as multiple Coulomb scattering with resultant losses in the Jovian atmosphere. It is shown that the magnitude and radial dependence of the losses are sufficient to explain the electron measurements, although the possibility that some other process may be more effective cannot be ruled out. The same dust population has, on the other hand, no significant effect on the plasma, which should therefore be transported essentially loss free, except within the Jovian ring, if there are no other processes involved. Comparison with the data shows that loss free transport outside the ring does indeed satisfy the measurement constraints. 相似文献
13.
The present analysis confirms the contention that the majority of Jupiter's decametric radio emissions occur when Io is above the northern magnetic hemisphere of Jupiter. However, a substantial portion of the non-Io-related component of source A was found to occur when Io was above southern magnetic latitudes of Jupiter. 相似文献
14.
The effect of parallel electrostatic field on the amplification of whistler mode waves in an anisotropic bi-Maxwellian weakly ionized plasma for Jovian magnetospheric conditions has been carried out. The growth rate for different Jovian magnetospheric plasma parameters forL = 5.6R
j has been computed with the help of general dispersion relation for the whistler mode electromagnetic wave of a drifted bi-Maxwellian distribution function. It is observed that the growth or damping of whistler mode waves in Jovian magnetosphere is possible when the wave vector is parallel or antiparallel to the static magnetic field and the effect of this field is more pronounced at low frequency wave spectrum. 相似文献
15.
Observations of Io suggest that it may have an atmosphere in which sodium vapor, ammonia, and nitrogen are important constituents. Several atmospheric models consisting of these gases are treated here. These are tested as a function of total content against the Pioneer 10 observations and for stability against escape. The results suggest that the atmosphere is very tenuous and that the interpretation of the ionosphere detected by Pioneer 10 by a static model may be inconsistent with the sodium cloud observations. It is postulated that ionization may also be escaping and that sodium may be comparable in content in the atmosphere with some molecular constituent such as NH3 or N2. Sodium and this molecular component then dominate the atmosphere. It is also suggested that particle precipitation contributes to heating of the atmosphere and to the production of ionization; furthermore, the difference between day- and nighttime ionospheres and possible trailing and leading side effects may relate to the nature of the particle energy distributions. These distributions may be the result of the peculiar interaction of Io with the Jovian magnetosphere. 相似文献
16.
William M. Sinton 《Icarus》1973,20(3):284-296
An atmosphere containing 0.5 cm atm of ammonia is assumed on Io. Such an atmosphere will be frozen at the unilluminated pole during the solstices, but will evaporate at the equinoctial seasons. The ammonia atmosphere will explain: (1) the posteclipse brightenings and their observed times of occurrence and nonocurrence; (2) the observed departure from a two-layer model beating curve upon emergence from eclipse; (3) the discordant temperatures obtained at 10 and 20 μm; and (4) discordant temperatures obtained at 10 and 20 μm during the total phase of an eclipse by Jupiter.In order to explain items 3 and 4 above, a proton flux in Jupiter's magnetosphere of 1.1 × 109 cm?2s? at an energy of 0.5MeV at io's distance from Jupiter is assumed. This flux is 40 times the flux in Divine's (1972) “upper-limit” model of the Jovian radiation belts, while the proton energy is eight times less. The proton flux, plus the solar ultraviolet and infrared flux absorbed by the ammonia, will heat the atmosphere to 245 ± 10°K. At this temperature the occultation atmospheric upper limit allows the addition of 4 cmatm of nitrogen. 相似文献
17.
Models are developed to describe the spatial distribution of gases emitted by Io and are applied to recent observations which indicate extensive gas clouds of hydrogen and sodium in orbit around Jupiter. Hydrogen and sodium atoms are emitted from Io with velocities in the range 2 to 3 km sec?1, with fluxes of about 1010 and 108cm?2sec?1 for hydrogen and sodium respectively. Hydrogen atoms may be formed by photodecomposition of gases such as NH3 or H2S released from the satellite surface and may escape thermally from an exosphere whose temperature is about 500 K. Sodium may be ejected from the surface by energetic particles or by ultraviolet radiation and it appears that a non-thermal mechanism drawing energy from Jupiter's magnetic field is required in order to account for its release to space. 相似文献
18.
We use the specific scintillations of jovian decametric radio sources (modulation lanes), which are produced by plasma inhomogeneities in the vicinity of that planet, to probe the inner magnetosphere of Jupiter. The positions and frequency drift of 1762 lanes have been measured on the DAM spectra from archives. A special 3D algorithm is used for space localization of field-aligned magnetospheric inhomogeneities by the frequency drift of modulation lanes. As a result, the main regions of the lane formation are found: the Io plasma torus; the magnetic shell of the Gossamer Ring at Thebe and Amalthea orbits; and the region above the magnetic anomaly in the northern magnetosphere. It is shown that modulation lanes reveal the depleted magnetic tubes in practically unvisited, innermost regions of the jovian magnetosphere. The local and probably temporal plasma enhancement is found at the magnetic shell of Thebe satellite. Hence, the modulation lanes are a valuable instrument for remote sensing of those parts of jovian magnetosphere, which are not studied yet in situ. 相似文献
19.
O.L. Hansen 《Icarus》1973,18(2):237-246
Eclipse observations of Jupiter's satellites Io, Europa, and Ganymede have been obtained in an 8 to 14-μm band pass during 1971. The simplest thermal model able to explain the data for each satellite is a two-layer surface structure with an upper layer, only a few millimeters thick, having low thermal conductivity consistent with fine rock powder or frost, and a subsurface having high thermal conductivity consistent with solid rock or dense ice. The upper layer on Io (γ = 1100 ± 100)2 appears to be different from that on Europa (γ = 3000 ± 1000) and Ganymede (γ = 3400 ± 700), but the two-layer model fits all three satellites. 相似文献
20.
Mass pickup may be an important process in the vicinity of the Jovian satellite Io and could be largely responsible for the slowing and deviation of the magnetospheric plasma flow in Io's vicinity. Theoretical treatments hitherto have treated a flow dominated by mass pickup near Io in a manner exactly analogous to the case where Io's immediate vicinity is treated as a simple electrical conductor. The analogy although instructive is not exact for it does not take account of the increased mass density in the flow downstream of Io. We point out that when correctly treated, mass pickup gives rise to a distinct wake structure behind Io. Observationally there is no way at present of distinguishing between dominant mechanisms using the Voyager 1 data; a wake pass is needed. 相似文献