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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., 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, [...]

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 [...]

Explores various methods by which the temperature of Neptune's satellite Triton may be determined. The apparent low emissivity of Triton's surface is also discussed. Explanation of photometry from Voyager's photopolarimeter experiment; Inconsistencies of low emissivity.

Reports on salts on Europa's surface detected by Galileo near the infrared mapping spectrometer. Where the distorted bands can be observed on the satellite of Jupiter; Suggestion that the laboratory spectra of hydrated salt minerals such as magnesium sulfates and sodium carbonates and mixtures of the minerals provide a close match to the Europa spectra.

Reports on observations from the Galileo spacecraft that shows spatially resolved infrared and ultraviolet wavelength spectra of Europa's leading, anti-jovian quadrant show absorption features resulting from hydrogen peroxide (H2O2). Indication of surface H2O2 concentrations of about 0.13 percent, by number, relative to water ice; Consistencies with radiolytic production of H2O2 by intense energetic particle bombardment; How Europa's surface chemistry is dominated by radiolysis.