Thirteen detailed maps of the first six (of ten) possible sites for a future Lander/Rover/Sample-return mission to Mars are either nearing completion or in review. Basic mosaic of all sites were available at 1:2 million scale. In addition to preparing new base maps, special enhancements were generated for computer mosaics and individual images that delineate the geologic units more clearly. Photoclinometric profiles that allowed measurement of the thicknesses of geologic units, the depth of channels, and the throw on faults were prepared. Crater counts were made for each geologic unit.

Although many radar profiles and images of the areas within 20 deg of Mercury's equator had been obtained from 1971, at both Goldstone and Arecibo radar facilities, surprisingly little geological analysis had been done with these data until recently. Topographic profiles and radar roughness reflectivity images which can be derived from these data will be crucial in completing the geological mapping of Mercury now underway at the U.S. Geological Survey. Earth based radar observations of Mercury and the other terrestrial planets as well are a potentially very valuable tool in the determination of the physical nature of their surfaces. Processing of available radar data must be completed to establish any systematic relationship between raar reflectivities and roughness, density, dielectric constant, and other related geological parameters.

Detailed study of channels in the Mangala and Kasei Valles regions of Mars strengthens a theory that the authors presented earlier: that channeling episodes have occurred at many different times and by several different mechanisms. The study utilized new, high-resolution, 1:500,000-scale maps compiled as base material for selecting candidate sites for a future Mars rover/lander/sample return spacecraft. Nestus Valles, west of Mangala Valles, are incised in young basaltic lava flows and are overlain by a very young volcanic unit, possibly a pyroclastic deposit. Crater statistics define the relative ages of the volcanic units that bound the ages of the very young, episodic, fluvial events that formed the channels. Samples collected at the Nestus site by a future lander/rover vehicle and returned to Earth for radiometric analysis would determine the age of these events more precisely. Similar relations exists for many small channels northeast of Mangala Valles. Narrow, young channels are incised in the floors of the intermediate-size valleys of Asopus, Hermus, and Abus Valles. At Abus, the mouth of a broad valley is buried by young basalt flows; a younger inner valley cuts into these flows and is buried, in turn, by a younger flow. A lobe of one ofmore » these flow invades and flows part way up the mouth of Taus Valles. In the Kasei Valles region, parts of the older, very broad, Kasei outflow channel are incised by fluvial grooving and contain streamlined islands; a younger, narrower, inner valley cuts the older valley; both valleys are buried by younger lobate basaltic lava flows.« less