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At least 19 records
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NASA NTRS1983

The Jovian magnetosphere

Research on Jovian magnetospheric physics from 1979 through 1982 is surveyed, with a focus on the observations of Voyagers 1 and 2. Jovian fields and plasmas are characterized in the order of their distance from the planet, and special emphasis is given to the Io plasma torus (IPT) in the 4.9-8-Jovian-radius region and to the extended Jovian magnetotail. Topics reviewed include synchrotron radiation, magnetic-field models, Na and S emissions in the IPT, aurora, the magnetic-anomaly model, IPT plasma diffusion-convection, Io-generated Alfven wave, plasma configuration beyond the IPT, low-energy charged particles, cosmic-ray-energy particles, particle acceleration, magnetic configuration, tail current sheet and plasma disc, magnetopause and magnetosheath, interplanetary ions of Jovian origin, and the Jovian magnetosphere at Saturnian distances.

Birmingham, T. J.↗
NASA NTRS2002

Magnetic Fluctuations in the Jovian Magnetosphere

The engine that drives the jovian magnetosphere is the mass added to the Io ion torus, accelerated to corotational velocities by field-aligned currents that couple the Io torus to the jovian ionosphere. The mass of the torus builds up to an amount that the magnetic forces cannot contain and the plasma, first slowly and then more rapidly, drifts outward. Numerous authors have treated this problem based first on the observations of the Pioneer 10 and 11 flybys; then on Voyager 1 and 2, and Ulysses; and finally most recently the Galileo orbiter. The initial observations revealed the now familiar magnetodisk, in which the field above and below the magnetic equator became quite radial in orientation and much less dipolar. The Galileo observations show this transformation to occur on average at 24 R(sub J) and to often be quite abrupt. These observations are consistent with outward transport of magnetized plasma that moves ever faster radially until about 50 R(sub J) on the nightside where the field lines stretch to the breaking point, reconnection occurs, and plasma and field islands are transported down the tail ultimately removing the mass from the magnetosphere that Io had deposited deep in the inner torus. The reconnection process creates empty flux tubes connected to Jupiter that are buoyant and thought to float inward and replace the flux carried out with the torus plasma. As described above, the jovian magnetosphere could very well be in a state of steady laminar circulation, but indeed it is not. The process is very unsteady and the wave levels can be very intense. The existence of these waves in turn can lead to processes that compete with the radial circulation pattern in removing plasma from the system. These waves can scatter particles so that they precipitate into the ionosphere. This process should be important in the Io torus where the atmospheric loss cone is relatively large and becomes less important as the loss cone decreases in size with radial distance. However, the Io torus is relatively quiet compared to the region outside the torus and it is not obvious without studying this scattering carefully whether the loss in the torus or out of the torus is greater and whether it can act rapidly enough to compete with the radial transport of ions to the tail in the life cycle of the mass added at Io. Closer to Io the ion cyclotron waves are most intense and possibly are associated with the losses in the Io flux tube. The waves are also diagnostic of both the Io atmospheric composition and the size and strength of the massloading process.

Russell, Christopher T.↗
NASA NTRS1979

Voyager 2 - Energetic ions and electrons in the Jovian magnetosphere

The passage of Voyager 2 through the Jovian magnetosphere demonstrated that this magnetosphere is highly variable, even as close as 10 Jupiter radii from the planet. The cosmic-ray subsystem measured the flux, elemental composition, and anisotropy of energetic particles. Its high sensitivity was particularly valuable during the long passage through the magnetotail, where particle fluxes were orders of magnitude less than in the inner magnetosphere and approached interplanetary values. The new data confirm earlier observations that the Jovian magnetosphere is a giant accelerator of particles - electrons, protons, and heavy ions, including sulfur. Both spatial and temporal changes are observed in the magnetosphere as compared to prior observations with Pioneer 10 and 11 and Voyager 1. It is suggested that the 10-hr modulation of interplanetary Jovian electrons may be associated with the arrival at the dawn magnetopause of a rarefaction region each planetary rotation.

Vogt, R. E.↗
NASA NTRS2001

A Global Magnetohydrodynamic Model of Jovian Magnetosphere

The goal of this project was to develop a new global magnetohydrodynamic model of the interaction of the Jovian magnetosphere with the solar wind. Observations from 28 orbits of Jupiter by Galileo along with those from previous spacecraft at Jupiter, Pioneer 10 and 11, Voyager I and 2 and Ulysses, have revealed that the Jovian magnetosphere is a vast, complicated system. The Jovian aurora also has been monitored for several years. Like auroral observations at Earth, these measurements provide us with a global picture of magnetospheric dynamics. Despite this wide range of observations, we have limited quantitative understanding of the Jovian magnetosphere and how it interacts with the solar wind. For the past several years we have been working toward a quantitative understanding of the Jovian magnetosphere and its interaction with the solar wind by employing global magnetohydrodynamic simulations to model the magnetosphere. Our model has been an explicit MHD code (previously used to model the Earth's magnetosphere) to study Jupiter's magnetosphere. We continue to obtain important insights with this code, but it suffers from some severe limitations. In particular with this code we are limited to considering the region outside of 15RJ, with cell sizes of about 1.5R(sub J). The problem arises because of the presence of widely separated time scales throughout the magnetosphere. The numerical stability criterion for explicit MHD codes is the CFL limit and is given by C(sub max)(Delta)t/(Delta)x less than 1 where C(sub max) is the maximum group velocity in a given cell, (Delta)x is the grid spacing and (Delta)t is the time step. If the maximum wave velocity is C(sub w) and the flow speed is C(sub f), C(sub max) = C(sub w) + C(sub f). Near Jupiter the Alfven wave speed becomes very large (it approaches the speed of light at one Jovian radius). Operating with this time step makes the calculation essentially intractable. Therefore under this funding we have been designing a new MHD model that will be able to compute solutions in the wide parameter regime of the Jovian magnetosphere.

Walker, Raymond J.↗
NASA NTRS1981

Energetic oxygen and sulfur in the Jovian magnetosphere

Measurements made in the Jovian magnetosphere by the cosmic ray subsystem on Voyager 1 and 2 are reported. Energy spectra of oxygen ions in the energy range 1-20 MeV/nuc between 5 and 20 Jovian radii are presented, and phase space densities are calculated. A steep positive radial gradient in the phase space density of the energetic oxygen ions is observed, indicating an inward diffusive flow. The upper limit on the rate at which oxygen ions with greater than 400 MeV/nuc-G diffuse across 10 Jovian radii is calculated to be 5 x 10 to the 21st ions per second, indicating that about 10 to the -7th of the ions from Io are accelerated to over 400 MeV/nuc-G and diffuse to 10 Jovian radii. Observations also suggest that oxygen and sulfur ions in the Io plasma torus diffuse radially outward, are nonadiabatically accelerated in a region outside 17 Jovian radii, and diffuse inward and outward from the accelerated region.

Gehrels, N.↗
NASA NTRS1974

Periodic escape of relativistic electrons from the Jovian magnetosphere

We adopt a model in which the Jovian magnetospheric tail is forced open by plasma that is accelerated out of the ionosphere by the centrifugal force of corotation. Any longitudinal asymmetry that exists in the ionospheric plasma source and/or the planetary magnetic field will cause a diurnal variation in the radial extent of the trapping region for energetic electrons. This diurnal variation in the extent of the particle trapping region can result in a time-dependent loss of relativistic electrons from the Jovian magnetosphere, modulated at the planetary rotation period. The diurnal trapping process may be relevant to the observation of electron pulses in interplanetary space during the Pioneer 10 approach to Jupiter.

Hill, T. W.↗
NASA NTRS1983

Physics of the Jovian magnetosphere

Jupiter's magnetic field and magnetosphere are considered along with the ionosphere, the low-energy plasma in the Jovian magnetosphere, the low-energy particle population, high-energy particles, and spectrophotometric studies of the Io torus. Other topics explored are related to the phenomenology of magnetospheric radio emissions, plasma waves in the Jovian magnetosphere, theories of radio emissions and plasma waves, and magnetospheric models. Attention is also given to aspects of plasma distribution and flow, microscopic plasma processes in the Jovian magnetosphere, symbols and acronyms, coordinate systems, and selected physical parameters of Jupiter and Io.

Dessler, A. J.↗
NASA NTRS1993

Electron distributions in the inner Jovian magnetosphere: Voyager 1 observations

Using several improvements in the analysis of the observations of the Low Energy Charged Particle (LECP) experiment on Voyager 1, electron phase space densities in the inner Jovian magnetosphere (5 - 10 R(sub J) were first calculated at constant first and second invariants (represented by mu and K, respectively), based on the LECP measurements. The calculated electron phase space density profiles show that in the inner Jovian magnetosphere there exist evident time and longitude variations, energetic electron injections, and present radial transport and distributed losses. To study the radial and pitch angle diffusions of Jovian electrons, we have calculated the phase space densities in the K-L space. It is found that the electron population in the inner Jovian magnetosphere seems to consist of two components: electrons radially diffusing from a main external source and electrons generated from local sources. The radially diffusing electrons have a relatively time stationary and isotropic distribution, while the locally created electrons mainly concentrate around the equatorial plane and have relatively lower energies, in comparison with the inward diffusing electrons. Consequently, the sources of precipitation losses to the ionosphere must be primarily electrons transported from outer sources, and the major precipitations occur in the inner magnetosphere (L less than 7.5 R(sub J). In the inner Jovian magnetosphere (L = 5 to approximately 10 R(sub J)) it is estimated that for electrons with magnetic moment mu = 300 MeV/G, the diffusion coefficient D is roughly 10(exp -8) to approximately 10(exp -6) R(exp 2)(sub J)/s, and the lifetime against the diffusion losses is of the order of 10(exp 4) to approximately 10(exp 6) s.

Ye, G.↗
NASA NTRS1976

Dynamics of the Jovian magnetosphere and energetic particle radiation

Inferences are drawn from Jovian magnetosphere data acquired in the flybys of Pioneer 10 and Pioneer 11. Data on the outer magnetosphere and the inner core, and on observed 10-hr variations in particle intensity, are summarized, with attention given to the immense size and complexity of the magnetosphere and the behavior of trapped charged particles. The data support the maintenance and acceleration of charged particles trapped in Jupiter's magnetic field by inward diffusion in violation of the third adiabatic invariant. Prodigious quantities of high-energy particles are found to escape from Jupiter into interplanetary space, and MHD waves in the circumjovian plasma are considered. Whether the 10-hr variations are spatial or temporal in origin is weighed in favor of the latter. Production and loss mechanisms for the particles, and the nature of the Jovian magnetosphere itself, are noted among questions remaining obscure.

Simpson, J. A.↗
NASA NTRS1980

Electrostatic waves in the Jovian magnetosphere

Observations by the plasma wave receivers on Voyagers 1 and 2 show that a wide variety of electrostatic waves are present within the Jovian magnetosphere and that the Jovian electrostatic waves are for the most part very similar to those observed in the terrestrial magnetosphere. Bands of emission near the upper hybrid resonance frequency in the dayside outer magnetosphere are detected between higher harmonics of the electron gyrofrequency. Inside of about 23 Jupiter radii, electron cyclotron harmonic emissions appear to be durable features of the inner Jovian magnetosphere and are extremely well confined to the Jovian magnetic equator. The cyclotron emissions extend from just above the local electron gyrofrequency to the upper hybrid resonance frequency.

Kurth, W. S.↗
NASA NTRS1979

The magnetic anomaly model of the Jovian magnetosphere - Predictions for Voyager

The magnetic anomaly model, in which the anomalously weak magnetic field region in the northern hemisphere of Jupiter influences the outer Jovian magnetosphere by one or more plasma interaction processes, has been put forth to account for the various observed Jovian magnetospheric phenomena that show evidence of Jovian longitudinal asymmetry or planetary spin periodicity. From this model, normalized by empirical fitting to Pioneer 10 and 11 flyby data and to ground-based radio data, a series of predictions are made that are subject to test by the forthcoming flybys of Jupiter by Voyagers 1 and 2. These predictions cover: (1) the longitude range and time intervals of enhanced interaction between Io (and possibly Europa) and Jupiter's ionosphere, (2) plasma, energetic particle, and magnetic field periodicities in the outer magnetosphere, and (3) the sub-spacecraft System III longitude and the time, modulo 10 hours, of the first and subsequent magnetopause crossings.

Dessler, A. J.↗
NASA NTRS1981

Ion anisotropies in the outer Jovian magnetosphere

Results are presented from Voyager 1 and 2 low-energy charged particle measurements of ion anisotropies in the outer Jovian magnetosphere (more than about 20 Jupiter radii). These anisotropies are the first observed from an instrument rotating in the spin plane of Jupiter. For the several ion species investigated, all the first-order anisotropies are strongly in the corotational sense throughout most of the Jovian magnetosphere and out to the magnetopause on the dayside. Evidence exists for a small component of outward flow in the corotating region. Beyond about 130-150 Jupiter radii along the Voyager outbound trajectories, the anisotropies suggest a magnetospheric wind flowing outward from Jupiter.

Carbary, J. F.↗
NASA NTRS1974

Configuration of the Jovian magnetosphere

A model is presented in which the Jovian magnetosphere is severely inflated by the centrifugal stress of partially corotating plasma streaming out along field lines from the ionosphere. The model is consistent with observations reported from the Pioneer 10 encounter, including the disk-like field configuration, the diurnal modulation of trapped-particle fluxes, and the inferred departure from rigid corotation in the outer magnetosphere. The field configuration is closed on the dayside, but on the nightside the plasma can force the magnetic field open to form a planetary wind flowing in the antisolar direction.

Hill, T. W.↗
NASA NTRS2000

Implications of Depleted flux Tubes in the Jovian Magnetosphere

A rare but persistent phenomenon in the jovian magnetosphere is the occurrence of apparently depleted flux tubes, whose magnetic pressures are significantly above ambient levels. These flux tubes occur about 0.25% of the observing time in the region of the Io torus in the Galileo high resolution data. The importance of these tubes is that they can return to the inner magnetosphere the magnetic flux that has been convected radially outward with the iogenic plasma to the tail. The paucity of these tubes is consistent with the expected flux return rates if the tubes are moving inward at an average rate of about 5-10 km/s in the torus. Depleted flux tubes have yet to be observed inside of the lo orbit where the plasma beta is lower than in the hot torus. Estimates of the plasma density outside the tube from plasma wave measurements enable the average perpendicular temperature to be obtained from the magnetic field change. Extrapolating this temperature back to lo, we obtain an average ion temperature of approximately 60 eV. These values are generally consistent with earlier Voyager observations but on the low side of their range of uncertainty, and agree quite well with contemporaneous Galileo measurements where these are available.

Russell, C. T.↗
NASA NTRS1976

Plasma density in the outer Jovian magnetosphere

We assume that the dipole wobble excites Alfven waves which propagate outward along the field lines. The plasma density in the outer Jovian magnetosphere is derived from the amplitude of such diurnal magnetic field variations, as measured by Pioneer 10. The number density obtained by this method is of the same order of magnitude as that derived from pressure balance, the dynamic pressure of the outflow being neglected. This result casts some doubt on the existence of a super-Alfvenic outflow in the Jovian magnetosphere.

Eviatar, A.↗
NASA NTRS1976

A review of the Jovian magnetosphere based upon Pioneer 10 and 11

A review and analysis are presented of data derived from the Pioneer 10 and Pioneer 11 flybys of Jupiter on the Jovian plasma, magnetic field, and energetic particles in circumjovian space. The design of the space probes is described along with the principal experiments flown. Overall features of the Jovian magnetosphere are drawn and contrasted with the earth's magnetosphere. The trajectories of the two space probes are contrasted and their data on Jupiter's plasmasphere are correlated. Isointensity contours and count rates of energetic particles are plotted, flux tubes within the Jovian magnetosphere are mapped, the ring current (plasma torus) encircling the planet is described, and possible effects of solar wind and of the moons immersed in Jupiter's magnetosphere are considered.

Trainor, J. H.↗
NASA NTRS1979

The phase of the ten-hour modulation in the Jovian magnetosphere /Pioneers 10 and 11/

The paper describes the study of the phase of the 10-hour modulation of energetic electrons seen by Pioneers 10 and 11 in the Jovian magnetosphere. Attention is given to the peaks rather than the valleys of each cycle because the peaks are where physically interesting features occur, such as particle acceleration, current sheets, etc. To identify the peaks, it is required that the instantaneous intensity be higher than the 5-hour running average and the 5-hour running average be greater than the 10-hour running average. These criteria select an interval rather than a point and it is determined that this interval is an appropriate estimate of the experimental uncertainty. When the phases of the peaks are plotted together, they create patterns which are discussed in terms of disk-like, clock-like, and rotating anomaly models of the magnetosphere. Each model fits some of the data, but no model explains all of the data convincingly. It is concluded that there is still no understanding of the configuration of the outer Jovian magnetosphere.

Fillius, W.↗
NASA NTRS1986

The Io Torus and the Jovian magnetosphere

The IUE monitored the physical conditions in the Jovian magnetospheric system using the in situ Voyager measurements as a basis for comparison. Both the Io plasma torus, observable in emission of S(+), S(++), and S(+3), and the Jovian H2 polar aurorae are accessible to the IUE short wavelength spectrograph. Despite significant short-term variations observed, the electron density and temperature structure of the torus has not changed appreciably in the 7 yr since the Voyager encounters. The total radiated power from the polar aurorae remained relatively constant during this period.

Feldman, P. D.↗