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Two giant ovals in Jupiter's southern atmosphere, vortices of counterclockwise-rotating winds, merged in a 3-week period, starting in March 2000. One of the ovals called FA was more than 60 years old; the other called BE was the product of two 60-year-old ovals (BC and DE) that merged in 1998 (A. Sanchez-Lavega et al. 1999, Icarus 142, 116-124). The merger took place when the ovals were southeast of the Great Red Spot and after the disappearance of a smaller, clockwise-rotating oval midway between them. The interaction began when the high-altitude oval clouds showed counterclockwise rotation about each other, followed by coalescence and shrinking. The interaction in deeper clouds did not include mutual rotation, but there was evidence of complex cloud structure during the merger. [C] 2001 Academic Press Key Words: Jupiter; atmosphere; atmospheric dynamics.

The motion of the Jupiter-Saturn planetary system near the 5:2 mean-motion resonance is modeled analytically in the frame of the planar general three-body problem. The topology of the phase space in the resonance and near-resonance domains is investigated in detail by means of surfaces of section and spectral map techniques. Various regimes of motion of the Jupiter-Saturn system are observed, and their domains are represented on the parameter plane defined by the total energy of the system and the parameter of proximity to the 5:2 resonance. The regions of transition between domains of different regimes of motion are characterized by chaotic motion. We show that there is a significant chaotic zone associated with the 5:2 mean-motion resonance, but large-scale excursions of the planet eccentricities are not possible in the planar three-body model. [C] 2001 Academic Press Key Words: jovian planets; planetary dynamics; resonances.

Prior to the Galileo probe entry in Jupiter's atmosphere, the ammonia abundance in the planet's deep atmosphere as deduced from microwave observations was thought to be close to the solar N value at P [is greater than] 3 bar and subsolar at P [is less than] 2 bar. Analysis of the attenuation of the probe radio signal during its descent in Jupiter's atmosphere suggested [NH.sub.3] to be 3.6 [+ or -] 0.5 times solar N at P [is greater than] 8 bar (Folkner et al. 1998). Assuming this high value is globally representative of the [NH.sub.3] abundance in Jupiter's deep atmosphere, we show in this article that to match Jupiter's microwave spectrum the ammonia abundance must, globally, decrease at pressures P ?? 4 bar, and reach subsolar (?? 0.5) values at P ?? 2 bar. We confirm earlier analysis of the 1.3-cm wavelength region indicating that the disk-averaged relative humidity must be of the order of 10% at P [is less than] 0.55 bar. We discuss various ways in which [NH.sub.3] could decrease globally at altitudes well below the level where the [NH.sub.3]-ice clouds form. We also present radio images of Jupiter taken with the VLA at 2, 3.6, and 6 cm wavelength in November/December 1995 and January 1996. The Galileo probe entered Jupiter's atmosphere on 7 December 1995, at a latitude of 6.5 [degrees] N, i.e., at the southern edge of the north equatorial belt (NEB). Simulations of our data suggest that the longitude-averaged [NH.sub.3] abundance in the NEB at the time of the Galileo probe entry is of the order of 50-70% of the value in the equatorial zone (EZ), while the [NH.sub.3] abundance in the EZ is about ?? 0.5 x solar N. This low ammonia abundance in the NEB must extend down to the ~4- to 6-bar level. [C] 2001 Academic Press

A principal components analysis was performed on Hubble Space Telescope WFPC2 images of Jupiter from October 1995 and October 1996. Global maps in the F410M, F555W, F673N, and F953N filters were analyzed. These are continuum wavelengths in Jupiter's spectrum, sensitive to reflection from the visible cloud deck. The primary principal components correspond approximately to gray spectral brightness variations, accounting for ~91% of the variance in the images, and a component with a red spectral slope, which accounts for ~8% of the variance. This color component probably corresponds to a constituent in the ammonia cloud deck. Another color component, which is blue/green, may correspond to upper tropospheric clouds or haze and accounts for ~1% of the image variance. Although small, this component may explain differences seen in the color of the Great Red Spot and other features. [C] 2001 Academic Press Key Words: Jupiter, atmosphere; atmospheres, composition.

High resolution optical (4193-6619 [Angstrom]) spectra of Io in eclipse show auroral emission in five lines: [[O.sub.I]] 6300, 6363, 5577 [Angstrom] and Na 5889, 5896 [Angstrom]. We conclude that Io's diffuse red emissions imaged by the Galileo Solid State Imager (P. E. Geissler et al. 1999, Science 285, 870-874) are due to impact or dissociative excitation of oxygen, while diffuse green emissions are caused by the impact or dissociative excitation of sodium. No emission lines were detected in the blue region of the spectra, suggesting that the intense emission observed above Io's equatorial plumes is due to a molecular species such as [SO.sub.2] or SO. [C] 2000 Academic Press Key Words: Io; aurorae; Jupiter; magnetosphere.

A numerical model to explore the possibility that the dissipation of two upward propagating internal gravity waves, identified in the temperature measurements of the Galileo Probe, provide the energy to maintain Jupiter's high thermospheric temperatures ~900 K is used. The propagation and dissipation of the gravity waves are simulated by a fun-wave model that is used to calculate the thermal mean-state forcing. The observed temperature is the result of this forcing and other energy sources. The equation of heat transfer, including the effects of eddy and molecular thermal diffusion, is solved to provide the gravity wave contribution to the steady-state temperature distribution. For the smallest values of eddy diffusion considered, the waves can heat the entire thermosphere, while for the largest values of eddy diffusion, the waves can cool the entire thermosphere. However, in all cases considered the net heating and cooling effects are not large, being typically ~15-20 K or less. To the extent that the Galileo data characterize gravity waves in Jupiter's atmosphere, gravity wave dissipation is unlikely to be the source of energy maintaining Jupiter's high thermospheric temperatures. Other waves not identified in the Galileo data or other energy sources must be responsible for heating the jovian thermosphere. We demonstrate that the viscous heating can only be calculated using the viscous stress tensor, and that the use of the wave mechanical energy flux divergence for this purpose in previous studies is invalid. [C] 2000 Academic Press Key Words: Jupiter; atmosphere; dynamics; aeronomy; structure.

The anti-Jovian hemisphere of Europa (the hemisphere opposite the one facing Jupiter) displays a complex array of fractures, including roughly concentric and arcuate ones. The geometry of this intriguing pattern on the icy surface of Europa resembles the textural features displayed by perlitic volcanic glass. We argue that fast cooling of a rhyolitic magma may serve as an analogue for fast supercooling of water leading to formation of amorphous ice (glassy water). We envisage two possible scenarios for ice melting and subsequent extremely fast supercooling: (1) massive subglacial volcanic activity or (2) a large impact on the anti-Jovian hemisphere. We suggest that extremely fast formation of amorphous ice on Europa would result in a fracture pattern geometrically equivalent to that observed in perlitic glass. Fast supercooling of water will initially lead to brine retention in the ice phase; however, after some time these brines would be laterally rejected toward fractures. Furthermore, as solidification progresses downward, a shrinking ocean would increase brine concentration. These brines would eventually escape to the surface via the fracture network. Finally, high-pressure crystallization of salts within fractures may provide an efficient mechanism for differential plate separation, horizontal movement, and formation of new fractures. Keywords: Europa, anti-Jovian, glassy water, supercooling, fractures, brines.

A model coupling an electron energy degradation code with a detailed synthetic spectrum of the [H.sub.2] Lyman and Werner band system is used to calculate the emerging auroral ultraviolet spectra from Jupiter's atmosphere excited by electrons with different initial energy distributions. The atmospheric model is adapted from the vertical P-T profile measured by the Galileo probe and mid-latitude model hydrocarbon photochemistry. Each altitude layer, with its own gas temperature, contributes to the emergent ultraviolet spectrum and the absorbers are vertically distributed within the source region of the auroral emissions. Examples of the calculated spectra are shown to validate the synthetic spectrum and to illustrate the importance of the electron energy distribution and the vertical structure. The model is then applied to the analysis of seven HST/GHRS spectra of the 1200-1700 [Angstrom] region obtained with 5-[Angstrom] resolution at various locations in the north and south Jovian aurora. These spectra have different color ratios which characterize the energy of the precipitated electrons, although they do not have a high enough spectral resolution to permit a determination of the [H.sub.2] temperature. We find that the characteristic energy of the assumed initial Maxwellian distribution ranges between 17 and 40 keV. A clear signature of acetylene absorption is observed near 1520, 1480, and 1440 [Angstrom] where the [C.sub.2][H.sub.2] cross section shows strong absorption peaks. The acetylene column abundance overlying the emission peak varies from 0.02 to 0.2 of the methane column. A better fit is obtained for some spectra when ethane absorption is added. The [C.sub.2][H.sub.6] column abundance varies from 0 to 0.5 of the methane column. These changes relative to methane are presumably the result of perturbations by heat released by the fast electron thermalization and/or perturbations to the hydrocarbon chemistry resulting from the production of H atoms by the aurora. A spectrum of the Io flux tube footprint and its trailing tail shows an ultraviolet color and hydrocarbon absorption quite similar to some of the main oval spectra. This observation suggests that the electrons of the Io flux tube are energized to a few tens of keV, similar to the electron precipitated in the main ovals and polar caps. Echelle spectra between 1216 and 1220 [Angstrom] at 0.07 [Angstrom] resolution are also compared with the model fitting best the mid-resolution spectra. It is found that the effective [H.sub.2] rovibrational temperature associated with the echelle spectra are significantly higher than predicted by the mid-latitude model. A large vertical temperature gradient just above the methane homopause due to large heating by auroral precipitation is a plausible explanation for this difference. [C] 2000 Academic Press

This paper addresses the question of up to what extent there are changes in the jovian jets as seen at cloud level and how they relate to the cloud morphology changes. We focus on the particularly interesting region at 24 [degrees] N where the most intense jovian jet as observed at visual wavelengths resides. The studied period goes from 1991 to 1998, and the analysis is based on CCD images obtained with ground-based telescopes, complemented with a set from the HST imagery archive in the spectral range from ~300 to 890 nm. The morphology of the North Temperate Belt (NTB) was characterized by the presence of a series of long-lived spots with lifetimes [is greater than] 4 years that formed in the anticyclonic flank of the jet at planetographic latitude 23.3 N following the development of the 1990 large-scale disturbance that changed the albedo of this belt (Sanchez-Lavega et al. 1991). They are rapidly moving mid-scale ovals (zonal velocity 123.9 [ms.sup.-1], mean size ~6500 km east-west times 3200 km north-south) with weak anticyclonic vorticity. The detailed structure of the zonal wind velocity profile of the 23.7 [degrees] N jet between 1994 and 1998 was also measured using both cloud tracking and a correlation technique based on zonal reflectivity profiles. The jet peak speed during the 1994-1998 period appeared to be about 50 [ms.sup.-1] slower and its shape broader in latitude when compared to that measured with the Voyager's in 1979. It seems that the differences in the profile between 1979 and the 1990s are related to the observed different cloud morphology in the region. Key Words: Jupiter; atmosphere; meteorology; dynamics.

We present a detailed analysis of Hubble Space Telescope (HST) Wide Field and Planetary Camera 2 (WFPC 2) images of the first 25 min of the impacts of Comet Shoemaker-Levy 9 fragments A and G with Jupiter and the post impact ejecta patterns observed 1-2 h after each impact event, with a brief analysis of the available observations of the first 25 min of the E and W events. Via a ballistic model we (i) constrain the initial time of impact and the initial velocity and elevation angle of the apex of each observed impactor; (ii) reproduce the shape and the motion of the sunlit A and G ejecta clouds utilizing the initial velocities constrained for the apex of each ejecta cloud and initial elevation angles ranging from 80 [degrees] to 60 [degrees] [+ or -] 5 [degrees]; and (iii) compare the ejecta pattern generated by particle trajectories consistent with the observed ejecta clouds to the observed postimpact ejecta pattern. We conclude that (i) the crescent patterns can be reconstructed from ballistic ejecta traveling on trajectories of elevation angles ranging from 70 [degrees] to 45 [degrees] and initial velocity equivalent to that constrained for the apex of each cloud; (ii) the streaks can be reconstructed from ballistic particles propelled up from the channel at velocities less than 8.5 [+ or -] 1 km [s.sup.-1]; and (iii) the altitude of the self-luminous radiation detected at the onset of the A, G, and W observations is inconsistent with the ballistic trajectories fit to the apex of the sunlit ejecta clouds. We believe that the discrepancy between the trajectories of the initial HST/WFPC 2 detections and the later images is an indication of distinctly different phenomena associated with the impacts of the comet fragments. The timing of these events indicates that the first event recorded in association with the G impact is consistent with the entry of the bolide and that the self-luminous radiation recorded ~120 s after the ballistically derived impact time for the A and G impacts may be consistent with the excitation of the jovian atmosphere and/or cometary debris in the path of shock fronts accelerating away from the respective impact fireballs. Given the uncertainty in the ballistically derived impact time, the initial detection of the W event may have corresponded to either the incoming bolide or atmospheric and/or cometary debris excitation initiated by the passing of a shock front associated with the impact fireball. Key Words: Comet Shoemaker-Levy 9, Jupiter, Hubble Space Telescope.

Wave disturbances due to the Shoemaker-Levy 9 (SL-9) cometary impacts into Jupiter's atmosphere have been simulated with a fully compressible (nonhydrostatic), time-dependent, nonlinear, axisymmetric, f-plane, finite difference computational scheme. Energy is released in a cylindrical region with a radius of 250 to 1000 km as suggested by models of the reentry of impact ejecta following the initial explosion. The model produces outward moving gravity waves at stratospheric altitudes with speeds and relative amplitudes in agreement with observations. The waves emerge from a cylindrical region of alternating inflow and outflow that extends high into the atmosphere in the main region of energy release. The disturbances originate as horizontally propagating waves at the periphery of this region, thereby providing an explanation for the observed large initial radius (~450-700 km) of the main ring. The model results suggest that the waves are made visible by the inflow of particulate impact debris into outward moving rings of wave horizontal convergence. The inner edge of the extensive clear zone outside of the main dark ring may be the divergence phase of the leading fast wave. The results of this study remove the necessity to invoke a stable, water-rich, wave-trapping layer in Jupiter's atmosphere in order to understand the Comet SL-9 observations of dark wave-like rings expanding radially away from the impact sites. Key Words: atmospheres, dynamics; Jupiter, atmosphere; comets, SL-9.

We searched the COBE DIRBE Sky and Zodi Atlas for a wake of dust trailing Mars and for Trojan dust near Jupiter's L5 Lagrange point. We compare the DIRBE images to a model Mars wake based on the empirical model of Earth's wake as seen by the DIRBE and place a 3-[Sigma] upper limit on the fractional overdensity of particles in the Mars wake of 18% of the fractional overdensity trailing Earth. We place a 3-[Sigma] upper limit on the effective emitting area of large (10- to 100-[micro]m-diameter) particles trapped at Jupiter's L5 Lagrange point of 6 x [10.sup.17] [cm.sup.2], assuming that these large dust grains are distributed in space like the Trojan asteroids. We would have detected the Mars wake if the surface area of dust in the wake scaled simply as the mass of the planet times the Poynting-Robertson time scale. Key Words: asteroids; extrasolar planets; interplanetary dust; Jupiter; Mars; resonances.

We present the results of the Infrared Space Observatory Short Wavelength Spectrometer (ISO-SWS) observations of Jupiter related to ammonia. We focus on two spectral regions; the first one (the 10-[micro]m region), ranging from 9.5 to 11.5 [micro]m, probes atmospheric levels between 1 and 0.2 bar, while the second one (the 5-[micro]m window), ranging from 4.8 to 5.5 [micro]m, sounds the atmosphere between 8 and 2 bar. The two spectral windows cannot be fitted with the same ammonia vertical distribution. From the 10-[micro]m region we infer an ammonia distribution of about half the saturation profile above the 1-bar level, where the N/H ratio is roughly solar. A totally different picture is derived from the 5-[micro]m window, where we determine an upper limit of 3.7 x [10.sup.-5] at 1 bar and find an increasing [NH.sub.3] abundance at least down to 4 bar. This profile is similar to that measured by the Galileo probe. The discrepancy between the two spectral regions most likely arises from the spatial heterogeneity of Jupiter, the 5-[micro]m window sounding dry areas unveiled by a locally thin cloud cover (the 5-[micro]m hot spots), and the 10-[micro]m region probing the mean jovian atmosphere above 1 bar. The [sup.15][NH.sub.3] mixing ratio is measured around 400 mbar from [v.sub.2] band absorptions in the 10-[micro]m region. We find the atmosphere of Jupiter highly depleted in [sup.15]N at this pressure level [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], while [([sup.15]N/[sup.14]N).sub.[direct sum]] = 3.68 x [10.sup.-3]]. It is not clear whether this depletion reveals the global jovian [sup.15]N/[sup.14]N ratio. Instead an isotopic fractionation process, taking place during the ammonia cloud condensation, is indicated as a possible mechanism. A fractionation coefficient [Alpha] higher than 1.08 would explain the observed isotopic ratio, but the lack of laboratory data does not allow us to decide unambiguously on the origin of the observed low [sup.15]N/[sup.14]N ratio. Key Words: atmospheres, composition; infrared observations; Jupiter, atmosphere.

Jupiter's polar regions are examined using ultraviolet (UV, 120-320 nm) images obtained with the Hubble Space Telescope Wide Field and Planetary Camera 2 over the period of 1994-1997. These images probe the stratospheric aerosols at pressures of a few tens of millibars. We discovered a UV-darkened segment in the polar shading just equatorward of the north polar hood that remained aligned with the southern-most portion of the north auroral oval. The darkened segment generally extended over 100 [degrees]-260 [degrees] System III longitude, and 39 [degrees]-53 [degrees] N planetocentric latitude in the F160W, F218W, and F255W images. No single type of feature in the F218W and F255W images appeared consistently aligned within the outline of the north auroral oval, but several transient features were observed. It is not certain whether these transient features were associated with auroral processes, or just coincidentally aligned. A 'south dark patch' was consistently observed within the outline of the south auroral oval and was temporally variable in size and shape. By tracking selected features, we obtained the first direct measurements of the zonal motions in Jupiter's high-latitude stratosphere. Primarily retrograde motions were observed from 41 [degrees] N to 60 [degrees] N. Both protrude and retrograde motions appeared from 48 [degrees] S to 71 [degrees] S. We propose that the asymmetric appearance of the polar hoods (R. A. West 1979, Icarus 38, 12-33; R. Wagener and J. Caldwell 1988, Icarus 74, 141-152) is influenced, in part, by meridional mixing in the stratosphere. Enhanced meridional mixing would tend to be more effective at dispersing the polar aerosols to lower latitudes in the north than in the south. Key Words: Jupiter, atmosphere; atmosphere dynamics; ultraviolet observations; HST.

Jupiter's low and mid-latitudes are examined using ultraviolet (UV) images obtained with the Hubble Space Telescope Wide Field and Planetary Camera 2 over the period of 1994-1997. Effective atmospheric pressures probed by the F160W, F218W, and F255W are estimated at 100, 165, and 370 mbar, respectively, at low latitudes. Far-ultraviolet images of Jupiter taken with the F160W filter reveal bright and dark latitudinal bands at low and mid-latitudes. These bands were found to be correlated with the zonal winds; the bright bands are at latitudes of subsidences, and the dark bands at upwellings. The sense of this correlation is opposite to that seen in visible images of Jupiter where the bright zones are located over upwellings, and dark belts over subsidences. The locations of the dark bands seen in the F160W images are consistent with enhanced concentrations of [NH.sup.3] and/or aerosols in the upwellings near the tropopause. Anticyclonic ovals, like the Great Red Spot, are regions of upwellings, and also appear dark in the F160W images. Temporal variations were also observed in the contrast of the low-latitude bands. An increase in the contrast of the low-latitude bands appeared to coincide with a visible wavelength broadening of the North Equatorial Belt that occurred in early to mid-1996. Changes at mid-southern latitudes were observed in the aftermath of the SL-9 impacts in July 1994. Key Words: Jupiter, atmosphere; ultraviolet observations; HST.

A comparison of laboratory spectra with Galileo data indicates that hydrated sulfuric acid is present and is a major component of Europa's surface. In addition, this moon's visually dark surface material, which spatially correlates with the sulfuric acid concentration, is identified as radiolytically altered sulfur polymers. Radiolysis of the surface by magnetospheric plasma bombardment continuously cycles sulfur between three forms: sulfuric acid, sulfur dioxide, and sulfur polymers, with sulfuric acid being about 50 times as abundant as the other forms. Enhanced sulfuric acid concentrations are found in Europa's geologically young terrains, suggesting that low-temperature, liquid sulfuric acid may influence geological processes., Europa is unique among Jupiter's moons. It is differentiated (1) with an icy crust that may melt from tidal heating to produce a subsurface ocean (2). The surface may be [...]

It has been established that argon, xenon and krypton in Jupiter's atmosphere are enriched to the same extent as the other heavy elements. This indicates that the planetesimals carrying these elements must have formed at temperatures lower than predicted by current models of giant-planet formation. It appears that the only explanation for the uniform enrichment of heavy elements seen on Jupiter is that these elements came from the planet in very cold icy planetesimals.

The 5-[[micro]meter] window in the spectrum of Jupiter is one of the few regions that gives access to the vertical structure of the troposphere between pressure levels of approximately 4 and 8 bar. Voyager/IRIS spectra obtained in 1979 during the Voyager flybys have been analyzed intensively over the past two decades. Most of these analyses concluded on a vertical cloud structure consisting of three layers: an ammonia cloud layer with a base around 0.5 bar, an ammoniumhydrosulfide layer at about 2 bar, and a water cloud layer with a base somewhere between 5 and 7 bar. However, the recent Galileo entry probe measurements of the vertical atmospheric structure in a hot spot region show a quite different picture. The data indicate only two cloud layers, at about 0.7 bar and 1.34 bar, and no significant cloud opacity between 2 and 22 bar, where the Probe measurements ended. New data from the Galileo/NIMS and ISO/SWS experiments agree with the Probe findings. The inclusion of cloud opacity between 5 and 7 bar in the model atmosphere results in a poor fit to the NIMS and ISO data. A comparison between Voyager/IRIS spectra and the ISO/SWS and Galileo/NIMS spectra shows a slope in the continuum level of the IRIS spectra for wavelengths shorter than 5 [[micro]meter], not present in either SWS spectrum or the NIMS spectra. We show that to fit the IRIS spectra, an additional opacity somewhere between 3 and 8 bar is needed in the model atmosphere. We suggest that, most likely, a calibration problem occurred with the Voyager/IRIS data in this spectral region, even though temporal variations in the deep atmospheric structure of Jupiter cannot be ruled out altogether. Key Words: Jupiter; atmosphere; infrared observations; hot spots; water cloud.

We present a new analysis of the 'quasi-quadrennial' oscillation (QQO), a quasi-periodic oscillation of longitude-mean temperatures and winds occurring at low latitudes in Jupiter's stratosphere that may be a phenomenon closely related to Earth's quasi-biennial oscillation (Leovy et al. 1991, Nature 354, 380-382). Measurements of 7.8-[[micro]meter] thermal emission from the jovian stratosphere acquired during the period 1991-1995 extend observations of this oscillation for an additional cycle beyond those presented in Orton et al. (1991, Science 252, 537-542), showing that this [approximately]4-yr-period signal has persisted for at least 15 yr. Numerical simulations of the QQO are performed to compare the brightness temperature patterns obtained to the ground-based measurements. By coupling these simulations with a radiative transfer model, we find that the amplitude of the oscillation must be significantly larger than previously estimated by Leovy et al. (1991). Long-period, large-scale equatorial waves on Jupiter are found to be ineffective in driving a QQO that produces the observed amplitude of the brightness temperature oscillations. Simulations in which the wave driving occurs through the interaction of small-scale, short-period gravity waves with their critical levels produce a QQO whose associated brightness temperature variations are in much better agreement with the observations. The amplitude of the QQO predicted by these simulations is large, suggesting that it may have a very significant effect on Jupiter's stratospheric thermal structure at low latitudes, some of which may be apparent in the vertical temperature profiles measured by the Galileo Atmospheric Structure Instrument and by the Voyager 1 radio occultation experiment.

Initial analysis of the results of a Doppler wind experiment conducted on the Galileo probe to Jupiter in Dec. 1995 indicates that the zonal winds of Jupiter are deep although they do not necessarily extend throughout the planet. Furthermore, the winds increase with depth although it is not as yet known why. These findings have significant implications for atmospheric dynamics.

The Galileo heavy ion counter is sensitive to ions with atomic numbers Z ≥ 6 and energies greater than ~6 MeV per nucleon. During Galileo's passage through Jupiter's inner magnetosphere, the observed composition of these heavy ions was consistent with the presence of singly ionized iogenic O, Na, and S and highly ionized solar C, O, and Ne. The solar component is absorbed more strongly by Io because its gyroradius is smaller than Io's diameter., Results from the Voyager spacecraft encounters with jupiter showed that energetic heavy ions form a major component of the trapped radiation in the inner magnetosphere (1). The dominant energetic heavy [...]

Earthly weather forecasters may not know for sure what tomorrow will bring, but at least they know what drives the winds: the heat of the sun warming Earth's atmosphere. But [...]

Changes in the speed of the Galileo probe caused by zonal winds created a small but measurable Doppler effect in the probe relay carrier frequency. Analysis of the probe relay link frequency allows direct measurements of the speed of Jupiter's zonal winds beneath the cloud tops. The deep winds were prograde and strong, reaching a sustained 190 to 200 meters per second at an attitude marked by a pressure of 24 bars. The depth and strength of the zonal winds severely constrain dynamic modeling of the deeper layers and begin to rule out many shallow weather theories., Direct measurements of planetary winds during earlier missions provide an impressive legacy for the Galileo Doppler wind experiment. The Pioneer, Venera, and Vega missions to Venus used a combination of [...]

Temperatures and pressures measured by the Galileo probe during parachute descent into Jupiter's atmosphere essentially followed the dry adiabat between 0.41 and 24 bars, consistent with the absence of a deep water cloud and with the low water content found by the mass spectrometer. From 5 to 15 bars, lapse rates were slightly stable relative to the adiabat calculated for the observed H2/He ratio, which suggests that upward heat transport in that range is not attributable to simple radial convection. in the upper atmosphere, temperatures of >1000 kelvin at the 0.01-microbar level confirmed the hot exosphere that had been inferred from Voyager occultations. The thermal gradient increased sharply to 5 kelvin per kilometer at a reconstructed altitude of 350 kilometers, as was recently predicted. Densities at 1000 kilometers were 100 times those in the pre-encounter engineering model., The Galileo probe, using instruments and techniques previously described (1), measured state properties of Jupiter's atmosphere from nanobar pressure levels to a final pressure of [is nearly equal to] 24 [...]

The Galileo probe performed the first in situ measurements of the atmosphere of Jupiter on 7 December 1995. The probe returned data until it reached a depth corresponding to an atmospheric pressure of ~24 bars. This report presents a brief overview of the origins and purpose of the mission. Science objectives, entry parameters and mission events, and results are described. The remaining reports address in more detail the individual experiments summarized here., The Galileo Entry Probe Mission to Jupiter conducted the first in situ measurements of the atmosphere of one of the outer giant planets. The information received from the probe defined [...]

Jupiter's water has gone missing, and researchers are scrambling to understand where it might be - and why it vanished. Theories about the giant planet's formation had predicted that its [...]