Locations on Mercury that produce ice-like radar responses lie withinimpact craters that have very cold, permanently shaded floors. The retention ofpossible ice deposits is determined largely by their temperature. We present model-calculated temperatures of flat surfaces and surfaces within bowl-shaped and flatflooredpolar impact craters. Our model includes appropriate insolation cycles,realistic crater shapes, multiple scattering of sunlight and infrared radiation, anddepth and temperature-dependent regolith thermophysical properties. Unshadedwater ice deposits are rapidly lost to sublimation on Mercury and the Moon.Meter-thick deposits of water ice are stable to evaporation over the age of thesolar system if located in the permanently shaded portions of flat-floored craterswithin 10° latitude of the poles of either planet. Results for craters associated withradar features on Mercury are consistent with stable water ice deposits if a thinregolith layer thermally insulates the lowest latitude deposits, reducing sublimationrates. A regolith cover also is a diffusion barrier, reduces losses from sputtering,impact vaporization, and exposure to H Lyα, and is implied independently by theradar observations. Impact craters near the lunar poles contain colder permanentlyshaded regions than those on Mercury.
During the first six orbits of the Galilee spacecraft's prime mission, theSolid State Imaging system acquired multispectral image mosaics of Jupiter'sGreat Red Spot, an equatorial belt/zone boundary, a "5-µm hotspot" similar to theGalilee Probe entry site, and two of the classic White Ovals. We present mosaicsof each region approximating their appearance at visible wavelengths and showingcloud height and opacity variations. The local wind field is derived by trackingcloud motions between multiple observations of each region with time separationsof roughly one and ten hours. Vertical cloud structure is derived in a companionpaper by Banfield et al.(1998). Galilee's brief, high-resolution observationscomplement Earth-based and Voyager studies, and offer local meteorologicalcontext for the Galileo Probe results. Images taken one hour apart reveal small,rapidly changing, high cloud features possibly analogous to terrestrialthunderstorms. Our results show that the dynamics of the zonal jets and largevortices have changed little since Voyager, with a few exceptions. We detect acyclonic current within the center of the predominantly anticyclonic Great RedSpot. The zonal velocity difference between 0°s and 6°S has increased by 20 m s^(-1).We measure a strong northeast flow approaching the hotspot. This flow indicateseither massive horizontal convergence or the presence of a large anticyclonicvortex southeast of the hotspot. The current compact arrangement of two WhiteOvals and a cyclonic structure greatly perturbs the zonal jets in that region.
