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Radio Doppler data, generated with NASA's Galileo spacecraft during its second encounter with Jupiter's moon Ganymede, are used to infer the locations and magnitudes of mass anomalies on Ganymede. We construct models for both surface and buried anomalies. With only one flyby and no global coverage, a solution for mass anomalies cannot be uniquely determined. However, we are able to constrain acceptable solutions for mass anomalies to four broad regions--a near polar region and three that are roughly equatorial. If the mass anomalies are constrained to lie at the surface, the centers of the regions are located near the coordinates (77[degrees] N, 333[degrees] W), (36[degrees] N, 0[degrees] W), (33[degrees] N, 130[degrees] W), and (7[degrees] N, 194[degrees] W). If the mass anomalies are located at the deep ice-rock interface 800 km below the surface, the regions' centers are approximately (65[degrees] N, 17[degrees] W), (32[degrees] N, 30[degrees] W), (37[degrees] N, 175[degrees] W), and (15[degrees] N, 211[degrees] W). For both models, the regions are up to a few thousand kilometers across. The magnitude of mass anomalies on the surface is on the order of [10.sup.17] kg. Mass anomalies at the ice--rock interface are on average no more than an order of magnitude larger ([10.sup.18] kg). There are two positive and two negative mass anomalies in both the surface and ice--rock interface models. One of the positive mass anomalies at the surface is associated with Galileo Regio. The other positive surface mass anomaly is located at high northern latitudes with no obvious geological association. Negative surface mass anomalies lie near Uruk Sulcus and between Perrine Regio and Barnard Regio near Sicyan Sulcus and Phrygia Sulcus. The locations of the ice--rock interface mass anomalies lie approximately radially below the surface anomalies. Positive mass anomalies at the surface could be associated with the silicate-rich ice or accumulated silicate layers of the dark regions. Negative mass anomalies at the surface could be associated with the relatively clean, low-lying ice of sulci. Alternatively, Ganymede's mass anomalies could be associated with the topography or other mass concentrations at the deep ice--rock interface. Keywords: Satellites of Jupiter; Ganymede; Surfaces, satellite

The intensities and distribution of > 1 MeV electrons in Jupiter's mid-magnetosphere have been characterized using the observations of the Galileo Energetic Particle Detector (EPD) instrument. Because of the more than 6 years of observation made by the EPD instrument in this intense radiation environment, and the inherent difficulties of measuring electrons with energies capable of penetrating shielding, it was necessary to check the performance of the instrument. Fortunately, in the mid-magnetosphere region particle intensities are such that the EPD instrument operated within its range of accurate counting. Salient results include: 1. Intensities that diminish exponentially with radial distance from 10 to approximately 18 [R.sub.J], with > 1 MeV electrons e-folding in about 1.9 [R.sub.J] and > 10 MeV electrons in about 1.2 [R.sub.J]. 2. A much more gradual decrease beyond 18 [R.sub.J] (e-folding in about 9.6 [R.sub.J] for > 1 MeV and about 5.3 [R.sub.J] for > 10 MeV. 3. A persistent intensity modulation at the planetary rotation period most strongly evident in the 10-18 [R.sub.J] region. 4. Secular variations that can be as large as factors of 100 most strongly evident in the 18-40 [R.sub.J] region. 5. Near order of magnitude variations of flux with magnetic latitude in the mid-magnetosphere, 24-25 [R.sub.J] between latitudes 0[degrees] and 15[degrees]. This manuscript describes the analysis and provides further detail on the results. Keywords: Jupiter, magnetosphere; Magnetospheres

Recent measurements of the high-energy, omni-directional electron environment by the Galileo spacecraft Energetic Particle Detector (EPD) have been analyzed in the range from 7 to 28 Jupiter radii. 10-min averages of these data between Jupiter orbit insertion in 1995 to the end of the mission have been analyzed to provide estimates of the electron differential fluxes at 1.5, 2, and 11 MeV in the jovian equatorial plane as a function of radial distance. These data provide a long term picture of the variations in the high-energy electron environment over the ~8 years of the Galileo mission. This paper reviews those measurements and the statistics associated with them for the 8 year period. In general, the data variations are well behaved with variations being within a factor of ~2 of a median value at a given distance from Jupiter. These results are analyzed in detail and the orbit variations discussed in the context of the overall data set. The results of this analysis of the long-term statistical variations in high-energy electron fluxes are directly applicable to models that estimate the effects of the radiation environment on Jupiter's moons and their atmospheres as they permit estimates of the possible range of radiation effects that might be expected. Keywords: Jupiter magnetosphere; Europa; Ganymede; Callisto

Using the helium abundance measured by Galileo in the atmosphere of Jupiter andinterior models reproducing the observed external gravitational field, we derivenew constraints on the composition and structure of the planet. We conclude that,except for helium which must be more abundant in the metallic interior than in themolecular envelope, Jupiter could be homogeneous (no core) or could have a centraldense core up to 12 [M.sub.[symmetry]]. The mass fraction of heavy elements is lessthan 7.5 times the solar value in the metallic envelope and between 1 and 7.2 timessolar in the molecular envelope. The total amount of elements other than hydrogenand helium in the planet is between 11 and 45 [M.sub.[symmetry]]. Key Words: Jupiter; interiors; planets; chemical abundances.

The Galileo-determined moment-of-inertia factor for Callisto of 0.406 [+ or -]0.039 (1[Sigma]) is consistent with only a small amount of ice-rock differentiation( Key words: Callisto; geophysics; interiors, satellites; planetary formation;satellites of Jupiter

The four largest satellites of Jupiter, called the Galilean satellites after their discoverer, are a mini solar system. They are about moon-sized to larger than Mercury, and the innermost satellite, [...], Five absorption features are reported at wavelengths of 3.4, 3.88, 4.05, 4.25, and 4.57 micrometers in the surface materials of the Galilean satellites Callisto and Ganymede from analysis of reflectance spectra returned by the Galileo mission near-infrared mapping spectrometer. Candidate materials include [CO.sub.2], organic materials (such as tholins containing C[equivalent]N and C-H), [SO.sub.2], and compounds containing an SH-functional group; [CO.sub.2], [SO.sub.2], and perhaps cyanogen [(CN)₂] may be present within the surface material itself as collections of a few molecules each. The spectra indicate that the primary surface constituents are water ice and hydrated minerals.

Identical in situ dust detectors are flown on board the Galileo and Ulysses spacecraft. They record impacts of micrometeoroids in the ecliptic plane at heliocentric distances from 0.7 to 5.4 AU and in a plane almost perpendicular to the ecliptic from -79 [degrees] to +79 [degrees] ecliptic latitude. The combination of both Ulysses and Galileo measurements yields information about the radial and latitudinal distributions of micron- and submicron-sized dust in the Solar System. Two types of dust particles were found to dominate the dust flux in interplanetary space. Interplanetary micrometeoroids covering a wide mass range from [10.sup.-16] to [10.sup.-6] g are recorded mostly inside 3 AU and at latitudes below 30 [degrees]. Interstellar grains with masses between [10.sup.-14] and [10.sup.-12] g have been positively identified outside 3 AU near the ecliptic plane and outside 1.8 AU at high ecliptic latitudes (>50 [degrees]). Interstellar grains move on hyperbolic trajectories through the planetary system and constitute the dominant dust flux (1.5 x [10.sup.-4] [m.sup.-2] [sec.sup.-1]) in the outer Solar System and at high ecliptic latitudes. To compare and analyze the Galileo and Ulysses data sets, a new model is developed based on J. Geophys. Res. 98, 17029-17048, Divine's (1993, 'five populations of interplanetary meteoroids' model. Both models describe the interplanetary meteoroid environment in terms of dust populations on distinct orbits. Taking into account the measured velocities and the effect of radiation pressure on small particles (described by the ratio of radiation pressure force to gravity, [Beta]), we define four populations of meteoroids on elliptical orbits and one population on hyperbolic orbit that can fit the micrometeoroid flux observed by Galileo and Ulysses. Micrometeoroids with masses greater than [10.sup.-10] g and negligible radiation pressure ([Beta] = 0) orbit the Sun on low to moderately eccentric orbits and with low inclinations ([less than or equal to] 30 [degrees]). Populations of smaller particles with mean masses of [10.sup.-11] g ([Beta] = 0.3), [10.sup.-13] g ([Beta] = 0.8), and 5 x [10.sup.-15] g ([Beta] = 0.3), respectively, have components with high eccentricities and have increasingly wider inclination distributions with decreasing mass. Similarities among the orbit distributions of the small particle populations on bound orbits suggest that all are genetically related and are part of an overall micrometeoroid complex that prevails in the inner Solar System. The high-eccentricity component of the small particle populations may actually be [Beta]-meteoroids which are not well characterized by our measurements. Our modeling suggests further that the interstellar dust flux is not reduced at Ulysses' perihelion distance (1.3 AU) and that it contributes about 30% of the total dust flux observed there.

The Galileo spacecraft is in orbit about Jupiter, studying Jupiter and the Galilean satellites (lo, Europa, Ganymede, and Callisto). Of these, only Io was known to have an atmosphere, which [...], The Galileo spacecraft performed six radio occultation observations of Jupiter's Galilean satellite Europa during its tour of the jovian system. In five of the six instances, these occultations revealed the presence of a tenuous ionosphere on Europa, with an average maximum electron density of nearly [10.sup.4] per cubic centimeter near the surface and a plasma scale height of about 240 ± 40 kilometers from the surface to 300 kilometers and of 440 ± 60 kilometers above 300 kilometers. Such an ionosphere could be produced by solar photoionization and jovian magnetospheric particle impact in an atmosphere having a surface density of about 108 electrons per cubic centimeter. If this atmosphere is composed primarily of [O.sub.2], then the principal ion is [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and the neutral atmosphere temperature implied by the 240-kilometer scale height is about 600 kelvin. If it is composed of [H.sub.2]O, the principal ion is [H.sub.3][O.sup.+] and the neutral temperature is about 340 kelvin. In either case, these temperatures are much higher than those observed on Europa's surface, and an external heating source from the jovian magnetosphere is required.

Before the Galileo mission to Jupiter there was little information on Europa's interior structure. Its mean density of 3018 ± 35 kg [m.sup.-3], determined from previous Jupiter missions (1), is [...], Doppler data generated with the Galileo spacecraft's radio carrier wave during two Europa encounters on 19 December 1996 (E4) and 20 February 1997 (E6) were used to measure Europa's external gravitational field. The measurements indicate that Europa has a predominantly water ice-liquid outer shell about 100 to 200 kilometers thick and a deep interior with a density in excess of about 4000 kilograms per cubic meter. The deep interior could be a mixture of metal and rock or it could consist of a metal core with a radius about 40 percent of Europa's radius surrounded by a rock mantle with a density of 3000 to 3500 kilograms per cubic meter. The metallic core is favored if Europa has a magnetic field.

The atmospheres of the giant planets (Jupiter, Saturn, Uranus, and Neptune) and Earth reach high temperatures in the low-pressure region of the upper atmosphere known as the thermosphere (1). On […]

The Galileo mission is a multidisciplinary international effort to explore the jovian system. Its primary objectives are to explore the atmosphere of the giant planet, the large Galilean satellites, and [...], The first images of Jupiter, Io, Europa, and Ganymede from the Galileo spacecraft reveal new information about Jupiter's Great Red Spot (GRS) and the surfaces of the Galilean satellites. Features similar to clusters of thunderstorms were found in the GRS. Nearby wave structures suggest that the GRS may be a shallow atmospheric feature. Changes in surface color and plume distribution indicate differences in resurfacing processes near hot spots on Io. Patchy emissions were seen while Io was in eclipse by Jupiter. The outer margins of prominent linear markings (triple bands) on Europa are diffuse, suggesting that material has been vented from fractures. Numerous small circular craters indicate localized areas of relatively old surface. Pervasive brittle deformation of an ice layer appears to have formed grooves on Ganymede. Dark terrain unexpectedly shows distinctive albedo variations to the limit of resolution.

In late June 1996, the Galileo spacecraft obtained its first remote sensing measurements within the jovian system. The Near Infrared Mapping Spectrometer (NIMS) performed spectroscopic and spectral mapping measurements of [...], The Near Infrared Mapping Spectrometer performed spectral studies of Jupiter and the Galilean satellites during the June 1996 perijove pass of the Galileo spacecraft. Spectra for a 5-micrometer hot spot on Jupiter are consistent with the absence of a significant water cloud above 8 bars and with a depletion of water compared to that predicted for solar composition, corroborating results from the Galileo probe. Great Red Spot (GRS) spectral images show that parts of this feature extend upward to 240 millibars, although considerable altitude-dependent structure is found within it. A ring of dense clouds surrounds the GRS and is lower than it by 3 to 7 kilometers. Spectra of Callisto and Ganymede reveal a feature at 4.25 micrometers, attributed to the presence of hydrated minerals or possibly carbon dioxide on their surfaces. Spectra of Europa's high latitudes imply that fine-grained water frost overlies larger grains. Several active volcanic regions were found on lo, with temperatures of 420 to 620 kelvin and projected areas of 5 to 70 square kilometers.

Jupiter's moon Io has repeatedly surprised planetary scientists. First, Io 's orbital position was unexpectedly found to control decametric radio emission from Jupiter's ionosphere (1). Early explanations suggested that the [...], During the inbound pass of the Galileo spacecraft, the magnetometer acquired 1 minute averaged measurements of the magnetic field along the trajectory as the spacecraft flew by Io. A field decrease, of nearly 40 percent of the background jovian field at closest approach to Io, was recorded. Plasma sources alone appear incapable of generating perturbations as large as those observed and an induced source for the observed moment implies an amount of free iron in the mantle much greater than expected. On the other hand, an intrinsic magnetic field of amplitude consistent with dynamo action at Io would explain the observations. It seems plausible that Io, like Earth and Mercury, is a magnetized solid planet.

The dust in the dust streams detected by the Galileo spacecraft near Jupiter originate from either the jovian gossamer ring or volcanoes on Io. The dust does not originate from the Shoemaker-Levy 9 comet as the comet has no stream activity. The dust storms detected by the Galileo dust detector are more intense and longer than those observed by the Ulysses spacecraft. The dust stream activity changes with time and there are significant differences between the intensity of the strongest and the weakest streams.

As the Galileo probe descended into Jupiter's atmosphere, the net flux radiometer (NFR) measured net solar and thermal radiation fluxes to determine where and how the atmosphere was being heated [...], The Galileo probe net flux radiometer measured radiation within Jupiter's atmosphere over the 125-kilometer altitude range between pressures of 0.44 bar and 14 bars. Evidence for the expected ammonia cloud was seen in solar and thermal channels down to 0.5 to 0.6 bar. Between 0.6 and 10 bars large thermal fluxes imply very low gaseous opacities and provide no evidence for a deep water cloud. Near 8 bars the water vapor abundance appears to be about 10 percent of what would be expected for a solar abundance of oxygen. Below 8 bars, measurements suggest an increasing water abundance with depth or a deep cloud layer. Ammonia appears to follow a significantly subsaturated profile above 3 bars. Unexpectedly high absorption of sunlight was found at wavelengths greater than 600 nanometers.

Jupiter is the largest planet in the solar system, almost 318 times more massive than Earth. Its gravitational field dominates the forces on its four largest satellites, discovered by Galileo [...], Doppler data generated with the Galileo spacecraft's radio carrier wave were used to measure Io's external gravitational field. The resulting triaxial field is consistent with the assumption that Io is in tidal and rotational equilibrium. The inescapable conclusion is that it has a large metallic core. If the core is a eutectic mixture of iron and iron sulfide, it comprises 20.2 ± 7.4 percent of the satellite's total mass with a radius that is about 52 percent of Io's mean radius of 1821.3 kilometers; if the core is pure iron, it comprises 10.5 ± 3.7 percent of the total mass with a radius of about 36 percent of the mean radius.

Space scientists are puzzled over Galileo's data of the Jupiter's stormy atmosphere and they are recalibrating their instruments and reexamining theories regarding Jupiter. The probe reveals that the planet is drier than thought and the lightning data reveals confusing results. Wind movement is different and stronger than expected. The result confirms the earlier theory of evolution of Jupiter. The probe shows the existence of organic material at low clouds but no sign of complex organic molecules which leaves less room for the existence of life on the planet.

The impact of comet Shoemaker-Levy 9 (SL9) into Jupiter in July 1994 stimulated an unparalleled set of astronomical observations. The instrument complement of the Galileo spacecraft, on its way to [...], The Galileo Photopolarimeter Radiometer experiment made direct photometric observations at 678 and 945 nanometers of several comet Shoemaker-Levy 9 fragments impacting with Jupiter. Initial flashes occurred at (fragment G) 18 July 1994 07:33:32, (H) 18 July 19:31:58, (L) 19 July 22:16:48, and (Q1) 20 July 20:13:52 [equivalent universal time coordinated (UTC) observed at Earth], with relative peak 945-nanometer brightnesses of 0.87, 0.67, 1.00, and 0.42, respectively. The light curves show a 2-second rise to maximum, a 10-second plateau, and an accelerating falloff. The Q1 event, observed at both wavelengths, yielded a color temperature of more than 10,000 kelvin at its peak.

The five images of 243 Ida (1), returned after Galileo's 28 August 1993 encounter with the asteroid (2), allow a preliminary characterization of its global properties and its surface geology. [...], The first images of the asteroid 243 Ida from Galileo show an irregular object measuring 56 kilometers by 24 kilometers by 21 kilometers. Its surface is rich in geologic features, including systems of grooves, blocks, chutes, albedo features, crater chains, and a full range of crater morphologies. The largest blocks may be distributed nonuniformly across the surface; lineaments and dark-floored craters also have preferential locations. Ida is interpreted to have a substantial regolith. The high crater density and size-frequency distribution (-3 differential power-law index) indicate a surface in equilibrium with saturated cratering. A minimum model crater age for Ida--and therefore for the Koronis family to which Ida belongs--is estimated at 1 billion years, older than expected.

Imaging objectives at Galileo's second lunar encounter with the moon (EM-2) were to extend multispectral mapping of the western limb and far side (1-5) to the northeastern limb and north [...], Multispectral images obtained during the Galileo probe's second encounter with the moon reveal the compositional nature of the north polar regions and the northeastern limb. Mare deposits in these regions are found to be primarily low to medium titanium lavas and, as on the western limb, show only slight spectral heterogeneity. The northern light plains are found to have the spectral characteristics of highlands materials, show little evidence for the presence of cryptomaria, and were most likely emplaced by impact processes regardless of their age.

On 29 October 1991, the Galileo space-craft flew past 951 Gaspra at a distance of 1600 km and obtained the first close-up views of an asteriod. Because Galileo's high-gain antenna [...], Galileo images of Gaspra reveal it to be an irregularly shaped object (19 by 12 by 11 kilometers) that appears to have been created by a catastrophic collisional disruption of a precursor parent body. The cratering age of the surface is about 200 million years. Subtle albedo and color variations appear to correlate with morphological features: Brighter materials are associated with craters especially along the crests of ridges, have a stronger 1-micrometer absorption, and may represent freshly excavated mafic materials; darker materials exhibiting a significantly weaker 1-micrometer absorption appear concentrated in interridge areas. One explanation of these patterns is that Gaspra is covered with a thin regolith and that some of this material has migrated downslope in some areas.

THE GALILEO SPACECRAFT ENCOUNTERED THE EARTH-moon system in December 1990 in the first of two flybys that are part of a sequence of planetary gravity assists that will deliver the [...], Multispectral images of the lunar western limb and far side obtained from Galileo reveal the compositional nature of several prominent lunar features and provide new information on lunar evolution. The data reveal that the ejecta from the Orientale impact basin (900 kilometers in diameter) lying outside the Cordillera Mountains was excavated from the crust, not hte mantle, and covers pre-Orientale terrain that consisted of both highland materials and relatively large expenses of ancient mare basalts. The inside of the far side South Pole--Aitken basinc (>2000 kilometers in diameter) has low albedo, red color, and a relatively high abundance of iron- and magnesium-rich materials. These features suggest that the impact may have penetrated into the deep crust or lunar mantle or that the basin contains ancient mare basalts that were later covered by highlands ejecta.

THE FEBRUARY 1990 GALILEO FLYBY provided a unique opportunity to investigate the clouds, motions, and deep-atmosphere composition of Venus with infrared imaging spectrscopy. The spectral range and spatial resolution of [...]

IMAGES OF THE NIGHT SIDE OF VENUS taken at near-infrared (NIR) wavelengths (1 to 2.5 [micrometer]) reveal bright and dark markings that rotate from east to west with periods of [...]

THE SOLID STATE IMAGING (SSI) camera on Galileo returned 77 useful images from Venus documenting the dynamical state of the cloud tops during the week after the encounter on 10 [...]

A MAJOR EVENT IN THE MORE THAN 6-year journey of the Gelileo spececraft to Jupiter was its encounter with Venus on 10 February 1990. The encounter provided an opportunity to [...]

THE OCCURRENCE OF LIGHTNING IN the atmosphere of Venus has been reported by several investigators but still remains controversial. The existence of lightning at Venus is important because it is [...]

OUR CURRENT KNOWLEDGE OF THE interaction of the solar wind with the planet Venus has been provided by a series of Mariner and Venera spacecraft and by Pioneer Venus Orbiter [...]

GALILEO FLEW BY VENUS ON ITS lengthy interplanetary voyage toward Jupiter. The spacecraft approached the planet from the downstream direction (Fig. 1) and skimmed the planetary bow shock, repeatedly traversing [...]

On 19 December 1996, the Galileo spacecraft completed the first stage of its reconnaissance of the Galilean satellites of Jupiter as it passed by Europa, the only large moon not [...], On 19 December 1996 as Galileo passed close to Jupiter's moon, Europa, the magnetometer measured substantial departures from the slowly varying background field of Jupiter's magnetosphere. Currents coupling Europa to Jupiter's magnetospheric plasma could produce perturbations of the observed size. However, the trend of the field perturbations is here modeled as the signature of a Europa-centered dipole moment whose maximum surface magnitude is ~240 nanotesla, giving a rough upper limit to the internal field. The dipole orientation is oblique to Europa's spin axis. This orientation may not be probable for a field generated by a core dynamo, but higher order multipoles may be important as they are at Uranus and Neptune. Although the data can be modeled as contributions of an internal field of Europa, they do not confirm its existence. The dipole orientation is also oblique to the imposed field of Jupiter and thus not directly produced as a response to that field. Close to Europa, plasma currents appear to produce perturbations with scale sizes that are small compared with a Europa radius.

The exospheric temperature of Jupiter's upper atmosphere as determined by Voyager solar occultation was 1100 ± 200 K at 1400 km above the 1 bar level (1). This is much [...], Temperatures in Jupiter's atmosphere derived from Galileo Probe deceleration data increase from 109 kelvin at the 175-millibar level to 900 ± 40 kelvin at 1 nanobar, consistent with Voyager remote sensing data. Wavelike oscillations are present at all levels. Vertical wavelengths are 10 to 25 kilometers in the deep isothermal layer, which extends from 12 to 0.003 millibars. Above the 0.003-millibar level, only 90- to 270-kilometer vertical wavelengths survive, suggesting dissipation of wave energy as the probable source of upper atmosphere heating.

On 7 December 1995, the Galileo spacecraft flew through Io's plasma torus, on a trajectory that included a close flyby of the moon at an altitude of 890 km [0.5 [...], Intense, magnetic field-aligned, bidirectional, energetic (> 15 kiloelectron volts) electron beams were discovered by the Galileo energetic particles detector during the flyby of lo. These beams can carry sufficient energy flux into Jupiter's atmosphere to produce a visible aurora at the footprint of the magnetic flux tube connecting lo to Jupiter. Composition measurements through the torus showed that the spatial distributions of protons, oxygen, and sulfur are different, with sulfur being the dominant energetic (>~10 kiloelectron volts per nucleon) ion at closest approach.

On 7 December 1995, the Galileo orbiter passed within 0.5 [R.sub.Io] (Io radii) above the surface of Jupiter's moon io. The magnetometer (1) recorded magnetic field vectors with 0.22-s time [...], Galileo magnetometer data at 0.22-second resolution reveal a complex interaction between Io and the flowing plasma of the Io torus. The highly structured magnetic field depression across the downstream wake, although consistent with a magnetized Io, is modified by sources of currents within the plasma that introduce ambiguity into the interpretation of the signature. Highly monochromatic ion cyclotron waves appear to be correlated with the local neutral particle density. The power peaks in the range of molecular ion gyrofrequencies, suggesting that molecules from Io can remain undissociated over a region of more than 15 Io radii around Io.

The Galileo dust detector system (DDS) (1) like its twin aboard Ulysses (2), is an impact ionization detector that measures the plasma cloud released upon impact of submicrometer- and micrometer-sized [...], About a hundred dust impacts per day were detected during the first week in December 1995 by Galileo during its approach to Jupiter. These impacts were caused by submicrometer-sized particles that were just above the detection limit. After the closest approach to lo on 7, December, impacts of these small particles ceased. This effect is expected for dust grains emitted from lo that exit the field of view of the instrument after the flyby. The impact rate of bigger micrometer-sized dust grains continued to increase toward Jupiter. These dust particles are in orbit about Jupiter or are interplanetary grains that are gravitationally concentrated near Jupiter.

The Galileo Photopolarimeter-Radiometer (PPR) experiment was designed to cover a broad wavelength range (410 nm to >45 μm) in order to (i) produce a synoptic set of measurements on properties [...], Photopolarimeter-Radiometer (PPR) maps of daytime temperatures on Ganymede at a resolution of 220 kilometers show the expected anticorrelation with albedo, but morning temperatures were about 10 kelvin warmer than expected. Europa had a subsolar temperature of 128 kelvin and a lower effective thermal inertia than either Ganymede or Callisto, and Io's night side was cooler than predicted by recent models, perhaps requiring revision of heat-flow estimates. The lowest 250-millibar temperatures in the Great Red Spot (GRS) generally corresponded to the visually darkest regions. Tempereratures remained cold north of the GRS, but they rose by as much as 6 kelvin to the south over the 2800-kilometer PPR resolution. A visually bright region northwest of the GRS was also relatively cold. It is likely that [NH.sub.3] clouds affected the determination of the 500-millibar temperature field, which appears qualitatively different.

During its 57 min of descent into Jupiter's atmosphere, the Galileo probe found that the speed of the zonal flow down to about the 20-bar level was nearly constant with [...], Measurements by the Galileo probe support the possibility that the zonal winds in Jupiter's atmosphere originate from convection that takes place in the deep hydrogen-helium interior. However, according to models based on recent opacity data and the probe's temperature measurements, there may be radiative and nonconvective layers in the outer part of the jovian interior, raising the question of how deep convection could extend to the surface. A theoretical model is presented to demonstrate that, because of predominant rotational effects and spherical geometry, thermal convection in the deep jovian interior can penetrate into any outer nonconvective layer. These penetrative convection rolls interact nonlinearly and efficiently in the model to generate and sustain a mean zonal wind with a larger amplitude than that of the nonaxisymmetric penetrative convective motions, a characteristic of the wind field observed at the cloud level on Jupiter.

In-situ measurements of the Jovian atmosphere conducted by the Galileo space probe show that the surface of Jupiter is generally dry and windy. Scientists postulate that this condition may be due to the lack of oxygen in the planetesimals that form Jupiter's atmosphere.

More than four decades ago, Burke and Franklin discovered that jupiter emitted radio waves (1). Much of the nonthermal, synchrotron radiation from jupiter originates from high-energy electrons that are trapped [...], The energetic particles investigation carried by the Galileo probe measured the energy and angular distributions of the high-energy particles from near the orbit of lo to probe entry into the jovian atmosphere. Jupiter's inner radiation region had extremely large fluxes of energetic electrons and protons; intensities peaked at ~2.2[R.sub.j] (where [R.sub.j] is the radius of Jupiter). Absorption of the measured particles was found near the outer edge of the bright dust ring. The instrument measured intense fluxes of high-energy helium ions (~62 megaelectron volts per nucleon) that peaked at ~1.5[R.sub.j] inside the bright dust ring. The abundances of all particle species decreased sharply at ~1.35[R.sub.j]; this decrease defines the innermost edge of the equatorial jovian radiation.