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"The most curious aspect of the topographic map is the striking difference between the planet’s low, smooth Northern Hemisphere and the heavily cratered Southern Hemisphere," which sits, on average, about three miles (five kilometers) higher than the north, Smith added. The MOLA data show that the Northern Hemisphere depression is distinctly not circular, and suggest that it was shaped by internal geologic processes during the earliest stages of martian evolution. 
The massive Hellas impact basin in the Southern Hemisphere is another
striking feature of the map. Nearly six miles (nine kilometers) deep and 1,300
miles (2,100 kilometers) across, the basin is surrounded by a ring of material that
rises 1.25 miles (about two kilometers) above the surroundings and stretches out
to 2,500 miles (4,000 kilometers) from the basin center.
This ring of material, likely thrown out of the basin during the impact of an asteroid, has a volume equivalent to a two-mile (3.5-kilometer) thick layer spread over the continental United States, and it contributes significantly to the high topography in the Southern Hemisphere. The difference in elevation between the hemispheres results in a slope from the South Pole to North Pole that was the major influence on the global-scale flow of water early in martian history. Scientific models of watersheds using the new elevation map show that the Northern Hemisphere lowlands would have drained three-quarters of the martian surface. On a more regional scale, the new data show that the eastern part of the vast Valles Marineris canyon slopes away from nearby outflow channels, with part of it lying a half-mile (about one kilometer) below the level of the outflow channels. "While water flowed south to north in general, the data clearly reveal the localized areas where water may have once formed ponds, " explained Dr. Maria Zuber of the Massachusetts Institute of Technology, Cambridge, MA, and Goddard. 
Right:
This dramatic three-dimensional visualization of Mars' north pole is based on elevation measurements
made by an orbiting laser. During the Spring and Summer of 1998 the Mars Orbiter Laser Altimeter (MOLA) flashed laser
pulses toward the Martian surface from the Global Surveyor spacecraft and recorded the time it took to detect the reflection.
This timing data has now been translated to a detailed topographic map of Mars' north polar terrain.
More information.
The amount of water on Mars can be estimated using the new data about the south polar cap and information about the North Pole released last year. While the poles appear very different from each other visually, they show a striking similarity in elevation profiles. Based on recent understanding of the North Pole, this suggests that the South Pole has a significant water ice component, in addition to carbon dioxide ice. The upper limit on the present amount of water on the martian surface is 800,000 to 1.2 million cubic miles (3.2 to 4.7 million cubic kilometers), or about 1.5 times the amount of ice covering Greenland. If both caps are composed completely of water, the combined volumes are equivalent to a global layer 66 to 100 feet (22 to 33 meters) deep, about one-third the minimum volume of a proposed ancient ocean on Mars. During the ongoing Mars Global Surveyor mission, the MOLA instrument is collecting about 900,000 measurements of elevation every day. These data will further improve the global model, help engineers assess the area where NASA's Mars Polar Lander mission will set down on Dec. 3, and aid the selection of future landing sites. MOLA was designed and built by the Laser Remote Sensing Branch of the Laboratory for Terrestrial Physics at Goddard. The Mars Global Surveyor mission is managed for NASA's Office of Space Science, Washington, DC, by the Jet Propulsion Laboratory, Pasadena, CA, a division of the California Institute of Technology.  More details about the MOLA instrument and science investigation can be found at: http://ltpwww.gsfc.nasa.gov/tharsis/mola.html |
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FIRST GLOBAL 3-D VIEW OF MARS REVEALS DEEP BASIN AND PATHWAYS FOR WATER FLOW - NASA HQ Press Release The Planet Mars - from the SEDS Nine Planets web site Life on Mars - A review of evidence of signs of life in the Allen Hills meteorite Mars Global Surveyor - home page Mars - by Percival Lowell, 1895 Related Stories:
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