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.

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 basin center.

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.

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 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 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.

See also The Global Topography of Mars and Implications for Surface Evolution, Science, Vol 284, May 28, 1999.

Visting the Map of Mars that you can click on different regions for more detailed information: http://tharsis.gsfc.nasa.gov/MOLA/Mars_topography_from_MOLA/