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Observations of seasonal variations of neutron flux from the high-energy neutron detector (HEND) on Mars Odyssey combined with direct measurements of the thickness of condensed carbon dioxide by the Mars Orbiter Laser Altimeter (MOLA) on Mars Global Surveyor show a latitudinal dependence of northern winter deposition of carbon dioxide. The observations are also consistent with a shallow substrate consisting of a layer with water ice overlain by a layer of drier soil The lower ice-rich layer contains between 50 and 75 weight % water, indicating that the shallow subsurface at northern polar latitudes on Mars is even more water rich than that in the south., Mars undergoes seasons in which volatile species, carbon dioxide (C[O.sub.2]) and, to a much lesser extent, water are exchanged between the atmosphere and surface (1, 2). The winter deposition in [...]

After 55 days of mapping by the High Energy Neutron Detector onboard Mars Odyssey, we found deficits of high-energy neutrons in the southern highlands and northern lowlands of Mars. These deficits indicate that hydrogen is concentrated in the subsurface. Modeling suggests that water ice-rich layers that are tens of centimeters in thickness provide one possible fit to the data., Some gullies on the surface of Mars have been attributed to recent water seepage and surface runoffs (1). To understand the hydrological processes on Mars that form surface features such [...]

Initial Magellan observations reveal a planet with high dielectric constant materials exposed preferentially in elevated regions with high slopes, ejecta deposits extending up to 1000 kilometers to the west of [...]

Evidence for Highly Reflecting Materials on the Surface and Subsurface of Venus RADAR AND RADIOMETRIC DATA from the Pioneer Venus spacecraft indicate that several regions on Venus have both high [...]

Describes the surface of Venus, mapped geologically by the Magellan spacecraft. Volcanic plains; Extensive volcanism; Tectonic deformation; Geologic and geomorphologic units; Conclusion.

Summarizes the principal features of the Magellan mission. Production of global, high-resolution image and altimetry data set of Venus; Analysis of Magellan data; Radar system data; Image performance; Future plans for mission.