Thanks to the topography data from MOLA, a high-resolution map of Mars was created that has aided in our understanding of Mars. One area of study where the detail in this map is useful is in understanding the establishment of the pathways for the flow of past water and the locations, sizes, and volumes of watersheds.

Water Basins and Surface Drainage

Scientist Bruce Banerdt did one such study. While it isn't possible to accurately reconstruct the surfac of Mars as it was at the time when liquid water may have existed on the surface, it is possible to model how water would behave if it existed on the surface today. Since there is evidence that the surface of Mars has had very little in the way of vertical surface change in several billion years, such a model could show the possible patterns on Martian surface water during the period of its wet history, as well as learn about possible erosion caused by flowing water.

The potential flow patterns on Mars were calculated using the high-precision MOLA topographic data. Assuming surface water, the data were used to trace the path of "streams" into "drainage basins", as well as the "flooding level" of each basin to find overflow points.

Figure 1 (above) shows what would be the 8 largest closed drainage basins on Mars, calculated from these flow patterns and plotted over a MOLA topographic map. Boundaries are equivalent to continental divides on the Earth. Blue arrows denote the the overflow points for each basin.

Figure 2 (above) shows what a very wet Mars might look like with all the basins filled to overflowing - similar to the situation over most of the Earth.

The three largest basins, the Northern Plains, Hellas, and Argyre, which dwarf te others, define the major planetary drainage divides. The area which would drain into the Northern Plains is large - over 3/4 of the surface! Any water south of about 45 degrees would end up in Hellas or Argyre.

The results shown in Banerdt's 2001 abstract on "Surface Drainage on Mars" state that "Several attributes of the drainage patterns shown in Figure 2 indicate that Mars was not subjected to significant erosion by flowing water over any extended period of time since the end of heavy bombardment...There is little evidence for mature tributary patterns, which migh tbe expected to survive as a subtle topographic signature...The high density of closed basins argues that erosional breaching and filling of basins, which is generally very efficient on the Earth, has been relatively unimportant in shaping the surface of Mars over the past several billion years."

In a scientific paper, Oden Ahronson agrees saying, "...surface runoff appears to have played at most a superficiial role in the evolution of the Martian landscape." Furthermore, "...topographically derived measurements indicate that the channels and associated drainage basins considered here have not been subject to significant sustained runoff erosion." North-South pole Elevation Difference

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.

On a more regional scale, the data from MOLA 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.

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 in 1998. 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.

Links & Resources

For more information, including hi-res images, please see the press release this article was partially adapted from.

Also see Banerdt, W.B. and A. Vidal, "Surface Drainage on Mars", Lunar and Planetary Science XXXII (2001).

http://www.lpi.usra.edu/meetings/lpsc2001/pdf/1488.pdf

See also Ahronson, O. et al, "Drainage basins and channel incision on Mars", PNAS, February 19, 2002.

http:/tharsis.gsfc.nasa.gov/MOLA/aharonson2002_pnas.pdf