An Overview of Energetic Particle Measurements in the Jovian Magnetosphere with the EPAC Sensor on Ulysses

Observations of ions and electrons of probable Jovian origin upstream of Jupiter were observed after a corotating interplanetary particle event. During the passage of Ulysses through the Jovian bow shock, magnetopause, and outer magnetosphere, the fluxes of energetic particles were surprisingly low. During the passage through the "middle magnetosphere," corotating fluxes were observed within the current sheet near the jovimagnetic equato. During the outbound pass, fluxes were variably directed; in the later part of the flyby, they were probably related to high-latitude phenomena.     

Jupiter's Magnetosphere: Plasma Description from the Ulysses Flyby

Plasma observations at Jupiter show that the outer regions of the Jovian magnetosphere are remarkably similar to those of Earth. Bow-shock precursor electrons and ions were detected in the upstream solar wind, as at Earth. Plasma changes across the bow shock and properties of the magnetosheath electrons were much like those at Earth, indicating that similar processes are operating. A boundary layer populated by a varying mixture of solar wind and magnetospheric plasmas was found inside the magnetopause, again as at Earth. In the middle magnetosphere, large electron density excursions were detected with a 10-hour periodicity as planetary rotation carried the tilted plasma sheet past Ulysses. Deep in the magnetosphere, Ulysses crossed a region, tentatively described as magnetically connected to the Jovian polar cap on one end and to the interplanetary magnetic field on the other. In the inner magnetosphere and lo torus, where corotation plays a dominant role, measurements could not be made because of extreme background rates from penetrating radiation belt particles.     

Hot plasma environment at jupiter: voyager 2 results

Measurements of the hot (electron and ion energies >/=20 and >/= 28 kiloelectron volts, respectively) plasma environment at Jupiter by the low-energy charged particle (LECP) instrument on Voyager 2 have revealed several new and unusual aspects of the Jovian magnetosphere. The magnetosphere is populated from its outer edge into a distance of at least approximately 30 Jupiter radii (R(J)) by a hot (3 x 10(8) to 5 x 10(8) K) multicomponent plasma consisting primarily of hydrogen, oxygen, and sulfur ions. Outside approximately 30 R(J) the hot plasma exhibits ion densities from approximately 10(-1) to approximately 10(-6) per cubic centimeter and energy densities from approximately 10(-8) to 10(-13) erg per cubic centimeter, suggesting a high beta plasma throughout the region. The plasma is flowing in the corotation direction to the edge of the magnetosphere on the dayside, where it is confined by solar wind pressure, and to a distance of approximately 140 to 160 R(J) on the nightside at approximately 0300 local time. Beyond approximately 150 R(J) the hot plasma flow changes into a "magnetospheric wind" blowing away from Jupiter at an angle of approximately 20 degrees west of the sun-Jupiter line, characterized by a temperature of approximately 3 x 10(8) K (26 kiloelectron volts), velocities ranging from approximately 300 to > 1000 kilometers per second, and composition similar to that observed in the inner magnetosphere. The radial profiles of the ratios of oxygen to helium and sulfur to helium (相似文献   

Magnetic field studies at jupiter by voyager 2: preliminary results

Data from the Goddard Space Flight Center magnetometers on Voyager 2 have yielded on inbound trajectory observations of multiple crossings of the bow shock and magnetosphere near the Jupiter-sun line at radial distances of 99 to 66 Jupiter radii (RJ) and 72 to 62 RJ, respectively. While outbound at a local hour angle of 0300, these distances increase appreciably so that at the time of writing only the magnetopause has been observed between 160 and 185 RJ. These results and the magnetic field geometry confirm the earlier conclusion from Voyager I studies that Jupiter has an enormous magnetic tail, approximately 300 to 400 RJ in diameter, trailing behind the planet with respect to the supersonic flow of the solar wind. Addi- tional observations of the distortion of the inner magnetosphere by a concentrated plasma show a spatial merging of the equatorial magnetodisk current with the cur- rent sheet in the magnetic tail. The spacecraft passed within 62,000 kilometers of Ganymede (radius = 2,635 kilometers) and observed characteristic fluctuations in- terpreted tentatively as being due to disturbances arising from the interaction of the Jovian magnetosphere with Ganymede.     

Imaging Obsearvations of Jupiter's Sodium Magneto-Nebula During the Ulysses Encounter

Jupiter's great sodium nebula represents the largest visible structure traversed by the Ulysses spacecraft during its encounter with the planet in February 1992. Ground-based imaging conducted on Mount Haleakala, Hawaii, revealed a nebula that extended to at least +/-300 Jovian radii (spanning approximately 50 million kilometers); it was somewhat smaller in scale and less bright than previously observed. Analysis of observations and results of modeling studies suggest reduced volcanic activity on the moon lo, higher ion temperatures in the plasma torus, lower total plasma content in the torus, and fast neutral atomic clouds along the Ulysses inbound trajectory through the magnetosphere. Far fewer neutrals were encountered by the spacecraft along its postencounter, out-of-ecliptic trajectory.     

Detection of singly ionized oxygen around jupiter

Forbidden emission from singly ionized oxygen at wavelengths of 3726 and 3729 angstroms has been detected in the inner Jovian magnetosphere. The emission is present between approximately 4 and approximately 7 to 8 Jovian radii from the planet and appears concentrated in the magnetic equator. The line intensity ratio indicates the same plasma characteristics as those derived from observations of forbidden sulfur emission.     

Ulysses at jupiter: an overview of the encounter

In February 1992, the Ulysses spacecraft flew through the giant magnetosphere of Jupiter. The primary objective of the encounter was to use the gravity field of Jupiter to redirect the spacecraft to the sun's polar regions, which will now be traversed in 1994 and 1995. However, the Ulysses scientific investigations were well suited to observations of the Jovian magnetosphere, and the encounter has resulted in a major contribution to our understanding of this complex and dynamic plasma environment. Among the more exciting results are (i) possible entry into the polar cap, (ii) the identification of magnetospheric ions originating from Jupiter's ionosphere, lo, and the solar wind, (iii) observation of longitudinal asymmetries in density and discrete wave-emitting regions of the lo plasma torus, (iv) the presence of counter-streaming ions and electrons, field-aligned currents, and energetic electron and radio bursts in the dusk sector on high-latitude magnetic field lines, and (v) the identification of the direction of the magnetic field in the dusk sector, which is indicative of tailward convection. This overview serves as an introduction to the accompanying reports that present the preliminary scientific findings. Aspects of the encounter that are common to all of the investigations, such as spacecraft capabilities, the flight path past Jupiter, and unique aspects of the encounter, are presented herein.     

Magnetic field studies at jupiter by voyager 1: preliminary results

Results obtained by the Goddard Space Flight Center magnetometers on Voyager 1 are described. These results concern the large-scale configuration of the Jovian bow shock and magnetopause, and the magnetic field in both the inner and outer magnetosphere. There is evidence that a magnetic tail extending away from the planet on the nightside is formed by the solar wind-Jovian field interaction. This is much like Earth's magnetosphere but is a new configuration for Jupiter's magnetosphere not previously considered from earlier Pioneer data. We report on the analysis and interpretation of magnetic field perturbations associated with intense electrical currents (approximately 5 x 10(6) amperes) flowing near or in the magnetic flux tube linking Jupiter with the satellite Jo and induced by the relative motion between Io and the corotating Jovian magnetosphere. These currents may be an important source of heating the ionosphere and interior of Io through Joule dissipation.     

Low-energy charged particle environment at jupiter: a first look

The low-energy charged particle instrument on Voyager was designed to measure the hot plasma (electron and ion energies greater, similar 15 and greater, similar 30 kiloelectron volts, respectively) component of the Jovian magnetosphere. Protons, heavier ions, and electrons at these energies were detected nearly a third of an astronomical unit before encounter with the planet. The hot plasma near the magnetosphere boundary is predominantly composed of protons, oxygen, and sulfur in comparable proportions and a nonthermal power-law tail; its temperature is about 3 x 10(8) K, density about 5 x 10(-3) per cubic centimeter, and energy density comparable to that of the magnetic field. The plasma appears to be corotating throughout the magnetosphere; no hot plasma outflow, as suggested by planetary wind theories, is observed. The main constituents of the energetic particle population ( greater, similar200 kiloelectron volts per nucleon) are protons, helium, oxygen, sulfur, and some sodium observed throughout the outer magnetosphere; it is probable that the sulfur, sodium, and possibly oxygen originate at 1o. Fluxes in the outbound trajectory appear to be enhancedfrom approximately 90 degrees to approximately 130 degrees longitude (System III). Consistent low-energy particle flux periodicities were not observed on the inbound trajectory; both 5-and 10-hour periodicities were observed on the outbound trajectory. Partial absorption of > 10 million electron volts electrons is observed in the vicinity of the Io flux tube.     

Voyager 2: energetic ions and electrons in the jovian magnetosphere

The Voyager 2 encounter has enhanced our understanding of earlier results and provided measurements beyond 160 Jupiter radii (R(J)) in the magnetotail. Significant fluxes of energetic sulfur and oxygen nuclei (4 to 15 million electron volts per nucleon) of Jovian origin were observed inside 25 R(J), and the gradient in phase space density at 12 R(J) indicates that the ions are diffusing inward. A substantially longer time delay versus distance was found for proton flux maxima in the active hemisphere in the magnetotail at Jovicentric longitudes lambda(III), = 260 degrees to 320 degrees than in the inactive hemisphere at lambda(III), = 85 degrees to l10 degrees . These delays can be related to the radial motion of plasma expanding into the magnetotail, and differences in the expansion speeds between the active and inactive hemispheres can produce rarefaction regions in trapped particles. It is suggested that the 10-hour modulation of interplanetary Jovian electrons may be associated with the arrival at the dawn magnetopause of a rarefaction region each planetary rotation.     

Magnetic field observations during the ulysses flyby of jupiter

The Jovian flyby of the Ulysses spacecraft presented the opportunity to confirm and complement the findings of the four previous missions that investigated the structure and dynamics of the Jovian magnetosphere and magnetic field, as well as to explore for the first time the high-latitude dusk side of the magnetosphere and its boundary regions. In addition to confirming the general structure of the dayside magnetosphere, the Ulysses magnetic field measurements also showed that the importance of the current sheet dynamics extends well into the middle and outer magnetosphere. On the dusk side, the magnetic field is swept back significantly toward the magnetotail. The importance of current systems, both azimuthal and field-aligned, in determining the configuration of the field has been strongly highlighted by the Ulysses data. No significant changes have been found in the internal planetary field; however, the need to modify the external current densities with respect to previous observations on the inbound pass shows that Jovian magnetic and magnetospheric models are highly sensitive to both the intensity and the structure assumed for the current sheet and to any time dependence that may be assigned to these. The observations show that all boundaries and boundary layers in the magnetosphere have a very complex microstructure. Waves and wave-like structures were observed throughout the magnetosphere; these included the longest lasting mirror-mode wave trains observed in space.     

Energetic Charged-Particle Phenomena in the Jovian Magnetosphere: First Results from the Ulysses COSPIN Collaboration

The Ulysses spacecraft made the first exploration of the region of Jupiter's magnetosphere at high Jovigraphic latitudes ( approximately 37 degrees south) on the dusk side and reached higher magnetic latitudes ( approximately 49 degrees north) on the day side than any previous mission to Jupiter. The cosmic and solar particle investigations (COSPIN) instrumentation achieved a remarkably well integrated set of observations of energetic charged particles in the energy ranges of approximately 1 to 170 megaelectron volts for electrons and 0.3 to 20 megaelectron volts for protons and heavier nuclei. The new findings include (i) an apparent polar cap region in the northern hemisphere in which energetic charged particles following Jovian magnetic field lines may have direct access to the interplanetary medium, (ii) high-energy electron bursts (rise times approximately 17 megaelectron volts) on the dusk side that are apparently associated with field-aligned currents and radio burst emissions, (iii) persistence of the global 10-hour relativistic electron "clock" phenomenon throughout Jupiter's magnetosphere, (iv) on the basis of charged-particle measurements, apparent dragging of magnetic field lines at large radii in the dusk sector toward the tail, and (v) consistent outflow of megaelectron volt electrons and large-scale departures from corotation for nucleons.     

Plasma Composition in Jupiter's Magnetosphere: Initial Results from the Solar Wind Ion Composition Spectrometer

The ion composition in the Jovian environment was investigated with the Solar Wind Ion Composition Spectrometer on board Ulysses. A hot tenuous plasma was observed throughout the outer and middle magnetosphere. In some regions two thermally different components were identified. Oxygen and sulfur ions with several different charge states, from the volcanic satellite lo, make the largest contribution to the mass density of the hot plasma, even at high latitude. Solar wind particles were observed in all regions investigated. Ions from Jupiter's ionosphere were abundant in the middle magnetosphere, particularly in the highlatitude region on the dusk side, which was traversed for the first time.     

Low-Energy Charged Particles in Saturn's Magnetosphere: Results from Voyager 1

The low-energy charged particle instrument on Voyager 1 measured low-energy electrons and ions (energies >/= 26 and >/= 40 kiloelectron volts, respectively) in Saturn's magnetosphere. The first-order ion anisotropies on the dayside are generally in the corotation direction with the amplitude decreasing with decreasing distance to the planet. The ion pitch-angle distributions generally peak at 90 degrees , whereas the electron distributions tend to have field-aligned bidirectional maxima outside the L shell of Rhea. A large decrease in particle fluxes is seen near the L shell of Titan, while selective particle absorption (least affecting the lowest energy ions) is observed at the L shells of Rhea, Dione, and Tethys. The phase space density of ions with values of the first invariant in the range approximately 300 to 1000 million electron volts per gauss is consistent with a source in the outer magnetosphere. The ion population at higher energies (>/= 200 kiloelectron volts per nucleon) consists primarily of protons, molecular hydrogen, and helium. Spectra of all ion species exhibit an energy cutoff at energies >/= 2 million electron volts. The proton-to-helium ratio at equal energy per nucleon is larger (up to approximately 5 x 10(3)) than seen in other magnetospheres and is consistent with a local (nonsolar wind) proton source. In contrast to the magnetospheres of Jupiter and Earth, there are no lobe regions essentially devoid of particles in Saturn's nighttime magnetosphere. Electron pitch-angle distributions are generally bidirectional andfield-aligned, indicating closed field lines at high latitudes. Ions in this region are generally moving toward Saturn, while in the magnetosheath they exhibit strong antisunward streaming which is inconsistent with purely convective flows. Fluxes of magnetospheric ions downstream from the bow shock are present over distances >/= 200 Saturn radii from the planet. Novel features identified in the Saturnian magnetosphere include a mantle of low-energy particles extending inward from the dayside magnetopause to approximately 17 Saturn radii, at least two intensity dropouts occurring approximately 11 hours apart in the nighttime magnetosphere, and a pervasive population of energetic molecular hydrogen.     

Preliminary results on the plasma environment of saturn from the pioneer 11 plasma analyzer experiment

The Ames Research Center Pioneer 11 plasma analyzer experiment provided measurements of the solar wind interaction with Saturn and the character of the plasma environment within Saturn's magnetosphere. It is shown that Saturn has a detached bow shock wave and magnetopause quite similar to those at Earth and Jupiter. The scale size of the interaction region for Saturn is roughly one-third that at Jupiter, but Saturn's magnetosphere is equally responsive to changes in the solar wind dynamic pressure. Saturn's outer magnetosphere is inflated, as evidenced by the observation of large fluxes of corotating plasma. It is postulated that Saturn's magnetosphere may undergo a large expansion when the solar wind pressure is greatly diminished by the presence of Jupiter's extended magnetospheric tail when the two planets are approximately aligned along the same solar radial vector.     

Radiation belts of jupiter

Pioneer 10 counted relativistic electrons throughout the magnetosphere of Jupiter, with the greatest fluxes being inside 20 Jupiter radii. The peak flux of electrons with energy greater than 50 million electron volts was 1.3 x 10(7) per square centimeter per second at the innermost penetration of the radiation belts.     

Plasma observations near saturn: initial results from voyager 2

Results of measurements of plasma electrons and poitive ions made during the Voyager 2 encounter with Saturn have been combined with measurements from Voyager 1 and Pioneer 11 to define more clearly the configuration of plasma in the Saturnian magnetosphere. The general morphology is well represented by four regions: (i) the shocked solar wind plasma in the magnetosheath, observed between about 30 and 22 Saturn radii (RS) near the noon meridian; (ii) a variable density region between approximately 17 RS and the magnetopause; (iii) an extended thick plasma sheet between approximately 17 and approximately 7 RS symmetrical with respect to Saturn's equatorial plane and rotation axis; and (iv) an inner plasma torus that probably originates from local sources and extends inward from L approximately 7 to less than L approximately 2.7 (L is the magnetic shell parameter). In general, the heavy ions, probably O(+), are more closely confined to the equatorial plane than H(+), so that the ratio of heavy to light ions varies along the trajectory according to the distance of the spacecraft from the equatorial plane. The general configuration of the plasma sheet at Saturn found by Voyager 1 is confirmed, with some notable differences and additions. The "extended plasma sheet," observed between L approximately 7 and L approximately 15 by Voyager 1 is considerably thicker as observed by Voyager 2. Inward of L approximately 4, the plasma sheet collapses to a thin region about the equatorial plane. At the ring plane crossing, L approximately 2.7, the observations are consistent with a density of O(+) of approximately 100 per cubic centimeter, with a temperature of approximately 10 electron volts. The location of the bow shock and magnetopause crossings were consistent with those previously observed. The entire magnetosphere was larger during the outbound passage of Voyager 2 than had been previously observed; however, a magnetosphere of this size or larger is expected approximately 3 percent of the time.     

Plasma observations near jupiter: initial results from voyager 1

Extensive measurements of low-energy positive ions and electrons were made throughout the Jupiter encounter of Voyager 1. The bow shock and magneto-pause were crossed several times at distances consistent with variations in the upstream solar wind pressure measured on Voyager 2. During the inbound pass, the number density increased by six orders of magnitude between the innermost magnetopause crossing at approximately 47 Jupiter radii and near closest approach at approximately 5 Jupiter radii; the plasma flow during this period was predominately in the direction of corotation. Marked increases in number density were observed twice per planetary rotation, near the magnetic equator. Jupiterward of the Io plasma torus, a cold, corotating plasma was observed and the energylcharge spectra show well-resolved, heavy-ion peaks at mass-to-charge ratios A/Z* = 8, 16, 32, and 64.     

Pioneer 11 encounter: preliminary results from the ames research center plasma analyzer experiment

Pioneer 11 observations of the interaction of Jupiter's magnetosphere with the distant solar wind have confirmed the earlier Pioneer 10 observations of the great size and extreme variability of the outer magnetosphere. The nature of the plasma transitions across Jupiter's bow shock and magnetopause as observed on Pioneer 10 have also been confirmed on Pioneer 11. However, the northward direction of the Pioneer 11 outbound trajectory and the distance of the final magnetopause crossing (80 Jupiter radii) now suggest that Jupiter's magnetosphere is extremely broad with a half-thickness (normal to the ecliptic plane in the noon meridian) which is comparable to or greater than the sunward distance to the nose.     

Low-Energy Hot Plasma and Particles in Saturn's Magnetosphere

The low-energy charged particle instrument on Voyager 2 measured low-energy electrons and ions (energies greater, similar 22 and greater, similar 28 kiloelectron volts, respectively) in Saturn's magnetosphere. The magnetosphere structure and particle population were modified from those observed during the Voyager 1 encounter in November 1980 but in a manner consistent with the same global morphology. Major results include the following. (i) A region containing an extremely hot ( approximately 30 to 50 kiloelectron volts) plasma was identified and extends from the orbit of Tethys outward past the orbit of Rhea. (ii) The low-energy ion mantle found by Voyager 1 to extend approximately 7 Saturn radii inside the dayside magnetosphere was again observed on Voyager 2, but it was considerably hotter ( approximately 30 kiloelectron volts), and there was an indication of a cooler ( < 20 kiloelectron volts) ion mantle on the nightside. (iii) At energies greater, similar 200 kiloelectron volts per nucleon, H(1), H(2), and H(3) (molecular hydrogen), helium, carbon, and oxygen are important constituents in the Saturnian magnetosphere. The presence of both H(2) and H(3) suggests that the Saturnian ionosphere feeds plasma into the magnetosphere, but relative abundances of the energetic helium, carbon, and oxygen ions are consistent with a solar wind origin. (iv) Low-energy ( approximately 22 to approximately 60 kiloelectron volts) electron flux enhancements observed between the L shells of Rhea and Tethys by Voyager 2 on the dayside were absent during the Voyager 1 encounter. (v) Persistent asymmetric pitch-angle distributions of electrons of 60 to 200 kiloelectron volts occur in the outer magnetosphere in conjunction with the hot ion plasma torus. (vi) The spacecraft passed within approximately 1.1 degrees in longitude of the Tethys flux tube outbound and observed it to be empty of energetic ions and electrons; the microsignature of Enceladus inbound was also observed. (vii) There are large fluxes of electrons of approximately 1.5 million electron volts and smaller fluxes of electrons of approximately 10 million electron volts and of protons greater, similar 54 million electron volts inside the orbits of Enceladus and Mimas; all were sharply peaked perpendicular to the local magnetic field. (viii) In general, observed satellite absorption signatures were not located at positions predicted on the basis of dipole magnetic field models.