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