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The nucleus of the Jupiter-family comet 19P/Borrelly was closely observed by the Miniature Integrated Camera and Spectrometer aboard the Deep Space 1 spacecraft on 22 September 2001. The 8-kilometer-long body is highly variegated on a scale of 200 meters, exhibiting large albedo variations (0.01 to 0.03) and complex geologic relationships. Short-wavelength infrared spectra (1.3 to 2.6 micrometers) show a slope toward the red and a hot, dry surface (≤345 kelvin, with no trace of water ice or hydrated minerals), consistent with ∼10% or less of the surface actively sublimating. Borrelly's coma exhibits two types of dust features: fans and highly collimated jets. At encounter, the near-nucleus coma was dominated by a prominent dust jet that resolved into at least three smaller jets emanating from a broad basin in the middle of the nucleus. Because the major dust jet remained fixed in orientation, it is evidently aligned near the rotation axis of the nucleus.

The Galileo Extreme Ultraviolet Spectrometer obtained a spectrum of Venus atmospheric emissions in the 55.0- to 125.0-nanometer (nm) wavelength region. Emissions of helium (58.4 nm), ionized atomic oxygen (83.4 nm), and atomic hydrogen (121.6 nm), as well as a blended spectral feature of atomic hydrogen (Lyman-β) and atomic oxygen (102.5 nm), were observed at 3.5-nm resolution. During the Galileo spacecraft cruise from Venus to Earth, Lyman-α emission from solar system atomic hydrogen (121.6 nm) was measured. The dominant source of the Lyman-α emission is atomic hydrogen from the interstellar medium. A model of Galileo observations at solar maximum indicates a decrease in the solar Lyman-α flux near the solar poles. A strong day-to-day variation also occurs with the 27-day periodicity of the rotation of the sun.

Simultaneous IMAGE EUV plasmaspheric images and Magnetospheric Plasma Analyzer (MPA) data from the Los Alamos National Laboratory's geosynchronous satellites are combined to understand plasmaspheric behavior and to quantify the global images. A brief review of the understanding of the plasmasphere as learned from in situ observations prior to the launch of IMAGE is given to place the results presented here into context.

Observations of the optical extreme ultraviolet spectrum of the Jupiter planetary system during the Voyager 1 encounter have revealed previously undetected physical processes of significant proportions. Bright emission lines of S III, S IV, and O III indicating an electron temperature of 10$^{5}$ K have been identified in preliminary analyses of the Io plasma torus spectrum. Strong auroral atomic and molecular hydrogen emissions have been observed in the polar regions of Jupiter near magnetic field lines that map the torus into the atmosphere of Jupiter. The observed resonance scattering of solar hydrogen Lyman $\\alpha $ by the atmosphere of Jupiter and the solar occultation experiment suggest a hot thermosphere (≥ 1000 K) with a large atomic hydrogen abundance. A stellar occultation by Ganymede indicates that its atmosphere is at most an exosphere.

Combined analysis of helium (584 angstroms) airglow and the atmospheric occultations of the star $\\delta $ Scorpii imply a vertical mixing parameter in Saturn's upper atmosphere of K (eddy diffusion coefficient) $\\sim $ 8 $\\times $ 10$^{7}$ square centimeters per second, an order of magnitude more vigorous than mixing in Jupiter's upper atmosphere. Atmospheric H$_{2}$ band absorption of starlight yields a preliminary temperature of 400 K in the exosphere and a temperature near the homopause of $\\sim $ 200 K. The energy source for the mid-latitude H$_{2}$ band emission still remains a puzzle. Certain auroral emissions can be fully explained in terms of electron impact on H$_{2}$, and auroral morphology suggests a link between the aurora and the Saturn kilometric radiation. Absolute optical depths have been determined for the entire C ring and parts of the A and B rings. A new eccentric ringlet has been detected in the C ring. The extreme ultraviolet reflectance of the rings is fairly uniform at 3.5 to 5 percent. Collisions may control the distribution of H in Titan's H torus, which has a total vertical extent of $\\sim $ 14 Saturn radii normal to the orbit plane.