An impact basin deep enough to swallow Mount Everest, surprising reverse slopes
in Valles Marineris, and the largest total range in elevations of any
planet in the solar system, highlight a global map of Mars that will influence
scientific understanding of the red planet for years.
Generated by the Mars Orbiter Laser Altimeter (MOLA), an instrument aboard
NASA's Mars Global Surveyor, the high-resolution map represents 640 million
elevation measurements as of June 30, 2001. The data were assembled
into a global grid with each point spaced 37 miles (60 kilometers) apart at
the equator, and less elsewhere. Each elevation point is known with an
accuracy of 42 feet (13 meters) in general, with large areas of the flat
northern hemisphere known to better than six feet (two meters).
Picture above is a flat map generated by the Mars Orbiter Laser Altimeter
(MOLA), an instrument aboard NASA's Mars Global Surveyor, the
high-resolution map represents 27 million elevation measurements gathered
in 1998 and 1999.
"This incredible database means that we now know the topography of Mars
better than many continental regions on Earth," said Dr. Carl Pilcher,
former Science Director for Solar System Exploration at NASA Headquarters,
Washington, DC. "The data will serve as a basic reference book for Mars
scientists for many years, and should inspire a variety of new insights
about the planet's geologic history and the ways that water has flowed
across its surface during the past four billion years."
"The full range of topography on Mars is about 19 miles (30 kilometers),
one and a half times the range of elevations found on Earth," noted Dr.
David Smith of NASA's Goddard Space Flight Center, Greenbelt, MD, the
principal investigator for MOLA.
"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.
Images above represent 90 degree 3D global views of Mars. Click on each globe for a larger view. Hi-Resolution website identified
at end of story.
The massive Hellas impact basin, shown at left, 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 2000 miles (3200 kilometers) from the
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
An estimate of the total volume of ice and sediments locked up at the poles
can be made from the elevation (thickness) to the surface and the areal
extent of the polar deposits. 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
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 Mars Global Surveyor mission, the MOLA instrument
collected about 900,000 measurements of elevation every day. These data
further improved the global model, and can aid the
selection of future landing sites, like the one shown at left.
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.
Links & Resources
For more information, including hi-res images, please see the press
release this article was adapted from.
The Global Topography of Mars and Implications for Surface Evolution, Science, Vol 284, May 28,
Visting the Map of Mars that you can click on different regions
for more detailed information: