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.     

Diverse plasma populations and structures in Jupiter's magnetotail

Jupiter's magnetotail is the largest cohesive structure in the solar system and marks the loss of vast numbers of heavy ions from the Jupiter system. The New Horizons spacecraft traversed the magnetotail to distances exceeding 2500 jovian radii (R(J)) and revealed a remarkable diversity of plasma populations and structures throughout its length. Ions evolve from a hot plasma disk distribution at approximately 100 R(J) to slower, persistent flows down the tail that become increasingly variable in flux and mean energy. The plasma is highly structured-exhibiting sharp breaks, smooth variations, and apparent plasmoids-and contains ions from both Io and Jupiter's ionosphere with intense bursts of H(+) and H(+)(3). Quasi-periodic changes were seen in flux at approximately 450 and approximately 1500 R(J) with a 10-hour period. Other variations in flow speed at approximately 600 to 1000 R(J) with a 3- to 4-day period may be attributable to plasmoids moving down the tail.     

Corotation Lag in Jupiter's Magnetosphere: Comparison of Observation and Theory

Voyager 1 plasma flow data are compared with a recent theory that predicted measurable departures from rigid corotation in Jupiter's magnetosphere as a consequence of rapid plasma production and weak atmosphere-magnetosphere coupling. The comparison indicates that the theory can account for the observed corotation lag, provided that the plasma mass production rate during the Voyager 1 encounter was rather larger than expected, namely approximately 10(30) atomic mass units per second.     

Preliminary pioneer 10 encounter results from the ames research center plasma analyzer experiment

Preliminary results from the Ames Research Center plasma analyzer experiment for the Pioneer 10 Jupiter encounter indicate that Jupiter has a detached bow shock and magnetopause similar to the case at Earth but much larger in spatial extent. In contrast to Earth, Jupiter's outer magnetosphere appears to be highly inflated by thermal plasma and therefore highly responsive in size to changes in solar wind dynamic pressure.     

Jupiter plasma wave observations: an initial voyager 1 overview

The Voyager I plasma wave instrument detected low-frequency radio emissions, ion acoustic waves, and electron plasma oscillations for a period of months before encountering Jupiter's bow shock. In the outer magnetosphere, measurements of trapped radio waves were used to derive an electron density profile. Near and within the Io plasma torus the instrument detected high-frequency electrostatic waves, strong whistler mode turbulence, and discrete whistlers, apparently associated with lightning. Some strong emissions in the tail region and some impulsive signals have not yet been positively identified.     

Magnetospheres of the galilean satellites

The plasma and field perturbations of magnetospheres that would surround magnetized galilean satellites embedded in the corotating jovian plasma differ from those produced by interaction with an unmagnetized conductor. If the intrinsic satellite dipole is antiparallel to that of Jupiter, the magnetosphere will be open. It is predicted that Io has an internal magnetic field with a dipole moment of 6.5 x 10(22) gauss-cubic centimeters antiparallel to Jupiter's, and Io's special properties can be interpreted on the basis of a reconnecting magnetosphere.     

Jupiter's Decametric Radio Emission and the Radiation Belts of Its Galilean Satellites

Many of the observed properties of Jupiter's decametric radiation may be explained by postulation that the inner Galilean satellites of Jupiter have magnetic properties that strongly distort Jupiter's magnetic field in the region of each satellite. Charged particles from Jupiter's radiation belts are trapped by these distorted fields and emit synchrotron radiation.     

ROSAT Observations of X-ray Emissions from Jupiter During the Impact of Comet Shoemaker-Levy 9

R?ntgensatellit (ROSAT) observations made shortly before and during the collision of comet Shoemaker-Levy 9 with Jupiter show enhanced x-ray emissions from the planet's northern high latitudes. These emissions, which occur at System III longitudes where intensity enhancements have previously been observed in Jupiter's ultraviolet aurora, appear to be associated with the comet fragment impacts in Jupiter's southern hemisphere and may represent brightenings of the jovian x-ray aurora caused either by the fragment impacts themselves or by the passage of the fragments and associated dust clouds through Jupiter's inner magnetosphere.     

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.     

Jupiter's nightside airglow and aurora

Observations of Jupiter's nightside airglow (nightglow) and aurora obtained during the flyby of the New Horizons spacecraft show an unexpected lack of ultraviolet nightglow emissions, in contrast to the case during the Voyager flybys in 1979. The flux and average energy of precipitating electrons generally decrease with increasing local time across the nightside, consistent with a possible source region along the dusk flank of Jupiter's magnetosphere. Visible emissions associated with the interaction of Jupiter and its satellite Io extend to a surprisingly high altitude, indicating localized low-energy electron precipitation. These results indicate that the interaction between Jupiter's upper atmosphere and near-space environment is variable and poorly understood; extensive observations of the day side are no guide to what goes on at night.     

Voyager 1 planetary radio astronomy observations near jupiter

We report results from the first low-frequency radio receiver to be transported into the Jupiter magnetosphere. We obtained dramatic new information, both because Voyager was near or in Jupiter's radio emission sources and also because it was outside the relatively dense solar wind plasma of the inner solar system. Extensive radio spectral arcs, from above 30 to about 1 megahertz, occurred in patterns correlated with planetary longitude. A newly discovered kilometric wavelength radio source may relate to the plasma torus near Io's orbit. In situ wave resonances near closest approach define an electron density profile along the Voyager trajectory and form the basis for a map of the torus. Detailed studies are in progress and are out-lined briefly.     

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.     

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.     

Equatorial X-ray Emissions: Implications for Jupiter's High Exospheric Temperatures

Observations with the High Resolution Imager on the Rontgensatellit reveal x-ray emissions from Jupiter's equatorial latitudes. The observed emissions probably result from the precipitation of energetic (>300 kiloelectron volts per atomic mass unit) sulfur and oxygen ions out of Jupiter's inner radiation belt. Model calculations of the energy deposition by such heavy ion precipitation and of the resulting atmospheric heating rates indicate that this energy source can contribute to the high exospheric temperatures(>800 kelvin at 0.01 microbar) measured by the Galileo probe's Atmospheric Structure Instrument. Low-latitude energetic particle precipitation must therefore be considered, in addition to other proposed mechanisms such as gravity waves and soft electron precipitation, as an important source of heat for Jupiter's thermosphere.     

Relation of Jupiter's Radio Emission at Long Wavelengths to Solar Activity

Since the spring of 1960 a strong positive correlation between Jupiter's decametric emission and solar decametric continuum emission observed at Boulder has been evident. The time delay of 1 to 2 days, with solar emission preceding Jupiter's emission, suggests that fast solar corpuscles, at velocities of the order of 0.1 c, are directly involved in the planet's atmosphere or magnetic field.     

Jupiter's Radiation Belts: Can Pioneer 10 Survive?

Model calculations of Jupiter's electron and proton radiation belts indicate that the Galilean satellites can reduce particle fluxes in certain regions of the inner magnetosphere by as much as six orders of magnitude. Average fluxes should be reduced by a factor of 100 or more along the Pioneer 10 trajectory through the heart of Jupiter's radiation belts in early December. This may be enough to prevent serious radiation damage to the spacecraft.     

Io's atmospheric response to eclipse: UV aurorae observations

The New Horizons (NH) spacecraft observed Io's aurora in eclipse on four occasions during spring 2007. NH Alice ultraviolet spectroscopy and concurrent Hubble Space Telescope ultraviolet imaging in eclipse investigate the relative contribution of volcanoes to Io's atmosphere and its interaction with Jupiter's magnetosphere. Auroral brightness and morphology variations after eclipse ingress and egress reveal changes in the relative contribution of sublimation and volcanic sources to the atmosphere. Brightnesses viewed at different geometries are best explained by a dramatic difference between the dayside and nightside atmospheric density. Far-ultraviolet aurora morphology reveals the influence of plumes on Io's electrodynamic interaction with Jupiter's magnetosphere. Comparisons to detailed simulations of Io's aurora indicate that volcanoes supply 1 to 3% of the dayside atmosphere.     

The impact of comet Shoemaker-Levy 9 sends ripples through the rings of Jupiter

Jupiter's main ring shows vertical corrugations reminiscent of those recently detected in the rings of Saturn. The Galileo spacecraft imaged a pair of superimposed ripple patterns in 1996 and again in 2000. These patterns behave as two independent spirals, each winding up at a rate defined by Jupiter's gravity field. The dominant pattern originated between July and October 1994, when the entire ring was tilted by about 2 kilometers. We associate this with the Shoemaker-Levy 9 impacts of July 1994. New Horizons images still show this pattern 13 years later and suggest that subsequent events may also have tilted the ring. Impacts by comets or their dust streams are regular occurrences in planetary rings, altering them in ways that remain detectable decades later.     

Cassini finds an oxygen-carbon dioxide atmosphere at Saturn's icy moon Rhea

The flyby measurements of the Cassini spacecraft at Saturn's moon Rhea reveal a tenuous oxygen (O(2))-carbon dioxide (CO(2)) atmosphere. The atmosphere appears to be sustained by chemical decomposition of the surface water ice under irradiation from Saturn's magnetospheric plasma. This in situ detection of an oxidizing atmosphere is consistent with remote observations of other icy bodies, such as Jupiter's moons Europa and Ganymede, and suggestive of a reservoir of radiolytic O(2) locked within Rhea's ice. The presence of CO(2) suggests radiolysis reactions between surface oxidants and organics or sputtering and/or outgassing of CO(2) endogenic to Rhea's ice. Observations of outflowing positive and negative ions give evidence for pickup ionization as a major atmospheric loss mechanism.     

Energetic particles in the jovian magnetotail

When the solar wind hits Jupiter's magnetic field, it creates a long magnetotail trailing behind the planet that channels material out of the Jupiter system. The New Horizons spacecraft traversed the length of the jovian magnetotail to >2500 jovian radii (RJ; 1 RJ identical with 71,400 kilometers), observing a high-temperature, multispecies population of energetic particles. Velocity dispersions, anisotropies, and compositional variation seen in the deep-tail (greater, similar 500 RJ) with a approximately 3-day periodicity are similar to variations seen closer to Jupiter in Galileo data. The signatures suggest plasma streaming away from the planet and injection sites in the near-tail region (approximately 200 to 400 RJ) that could be related to magnetic reconnection events. The tail structure remains coherent at least until it reaches the magnetosheath at 1655 RJ.