RADAR-DERIVED TOPOGRAPHY OF LOW SOUTHERN LATITUDES OF MARS

A series of delay-Doppler observations of Mars were made with the Goldstone radar facility at 3.5- and 13-cm wavelengths during the 1988 and 1990 oppositions. These oppositions provided particularly good opportunities for radar studies because of the relatively close approach of Mars during 1988 and because of improvements in the Goldstone antenna and the 3.5-cm radar system made prior to these observations. The 1988 and 1990 radar results consist of 19 tracks which cover the southern equatorial region of Mars from 3.6°S to 25.1°S. The topographic profiles derived from these observations have a horizontal resolution of 0.05° longitude (∼3 km) and a vertical resolution of 100 m. Major structures surveyed include Tyrrhena Patera, Melas Dorsa, Nectaris Fossae, the large impact basin Huygens, and the long channel Ma'adim Vallis. Ma'adim Vallis was crossed at subradar latitudes of 21.0°S, 22.4°S, and 25.1°S, and the channel depths at these locations are 2.3-2.5 km, 1.8 km, and 0.4 km, respectively. The average slope of the Ma'adim Vallis channel floor between the three radar profiles is 0.3+0.3-0.2%. Also included in the radar data are several sites in the heavily cratered southern highlands where aqueous sedimentation may have occurred early in the history of Mars. All of the possible aqueous sedimentation sites surveyed by groundbased radar are found to be local topographic lows with depths ranging from <200 to 800 m. The inflow valley areas adjacent to these sites generally have average surface slopes of about 1%. In the case of one possible aqueous sedimentation basin in the Margaritifer Sinus SE region, the measured basin depth of 800 m is comparable to the range of water depths which could have resulted from a single, complete discharge of the associated aquifer. Aquifer recharge was probably necessary, however, to have provided enough water to transport the sediment eroded from the inflowing valleys. © 1993 by Academic Press, Inc.