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Studying the Face of Mars
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By Kathy Sawyer
Images by NASA/Jet Propulsion Laboratory/Malin Space Science Systems

As the Mars Global Surveyor beams home unprecedented images, our assumptions about the red planet explode.

Get a taste of what awaits you in print from this compelling excerpt.

On this particular spring morning Edgett was escorting me on a virtual flying tour over Mars’s surface. Exhibit A was a disheveled-looking region known as Gorgonum Chaos. Here, captured in the Surveyor images, we saw part of a rugged crater wall that had collapsed into a gully with a number of deep, sinuous channels fanning out, ending abruptly in an apron of deposited material.

In shape the features resembled gully washes in the American West. The flows appeared to come to a sudden halt, suggesting the material was thick—perhaps liquid filled with dirt and debris. Mud on Mars? But what really brought up the goose bumps was the panoramic repetition of the startling features. As the flight continued along a strip of the planet’s surface, the flow patterns showed up on the cliff walls and escarpments of other craters, mesas, and troughs, always erupting near their tops, always apparently from the same geologic layer 100 to 500 meters (328 to 1,640 feet) down.

The evidence disturbed the scientists in more than one respect. First, conditions on Mars are such that any water reaching the surface supposedly would not remain liquid for very long but would boil, freeze, or poof into vapor. Second, from the absence of craters, sand dunes, or anything else on top of the gullies, they appeared to have formed very recently, possibly as recently as yesterday.

By this time the signature of weeping or seeping liquid had shown up in some 200 Surveyor images. Most of the evidence was found, strikingly, in some of the coldest places on the surface—on shadowed slopes facing the poles, in clusters scattered around latitudes higher than 30 degrees—rather than at the warmer equatorial latitudes. This suggested that the flows contained frozen volatiles, substances that would vaporize if exposed to the warmth of sunlight.

Malin and Edgett had been puzzling over these images for more than a year, trying to come up with an explanation that would point to something other than liquid water before publishing their discovery. “We were dragged kicking and screaming to this conclusion,” Edgett said. But they could find no plausible “dry” explanation. And proposals for other substances that might behave as liquids on the Martian surface raised so many other questions that they failed to solve the problem.

Get the whole story in the pages of National Geographic magazine.

We offer this forum board in Spanish and English. If Mars is livable for humans, should we go there? Join the discussion.

Les ofrecemos este forum en español y en inglés. ¿Es que deberíamos visitar Marte si los humanos pudiéramos vivir ahí? Únase a la discusión.

Sights and Sounds
NASA scientist Jim Garvin narrates a multimedia slideshow of the latest extraordinary images from Mars.

In More to Explore the National Geographic magazine team shares some of its best sources and other information. Special thanks to the Research Division.

A technical glitch that delayed the start of Mars Global Surveyor’s primary mapping mission by a year provided scientists with an unexpected bonus. When one of its solar panels did not deploy correctly, the spacecraft was left vulnerable to damaging vibrations during the aerobraking phase—when the craft was maneuvered into its circular mapping orbit by using atmospheric drag to slow it down. Operators revised the aerobraking schedule, allowing the craft to dip ever so slightly into the atmosphere with each orbit. During the time it took MGS to settle into its final orbit 240 miles [386 kilometers] above Mars’s surface, it recorded images and data it never would have otherwise.

Images made with the Mars Orbital Camera during aerobraking showed layering in the cliff walls of the huge Valles Marineris canyon system. Detail returned in these early images showed stratigraphy in the Martian crust at a scale never seen before—down to a few tens of meters. The images also showed lava flows that seemed much younger than anticipated—perhaps less than a hundred million years.

Another dramatic discovery, by the spacecraft’s magnetometer, showed curious strips in the crust that are apparently the remnants of a now defunct global magnetic field. The Earth generates a global magnetic field by the spinning of an interior molten core, but the MGS observations show that on Mars such a mechanism must have shut down early in the planet’s history. Another instrument, the Thermal Emission Spectrometer, searched for the pattern of water-generated minerals on the surface during low aerobraking passes. These and other startling discoveries clued scientists into realizing that MGS was going to show them a Mars they had never imagined.

Mars Global Surveyor finished its primary mapping mission on January 31, 2001, after measuring and imaging the planet for one Mars year, about two Earth years. The spacecraft is expected to collect data for at least one more year.

Jet Propulsion Laboratory, NASA
First stop for learning about the Mars Global Surveyor (MGS) mission, this includes numerous links to other good sites.

Malin Space Science Systems
All MGS images are presented on the site of this company, which designs, develops, and operates instruments that fly on robotic spacecraft.

National Space Science Data Center, NASA
For information on spacecraft that have explored our solar system.

Space Science Program, NASA
For more information on past, present, and future missions.


Beatty, J. Kelly, and others. The New Solar System, 4th ed. Sky Publishing Corporation, 1999.

Carr, Michael H. The Surface of Mars. Yale University Press, 1981.

Lowell, Percival. Mars and its Canals. The Macmillian Company, 1907.

Malin, Michael C. and Kenneth S. Edgett. “Evidence for Recent Groundwater Seepage and Surface Runoff on Mars,” Science (June 30, 2000), 2330-2335.

Mariner 9 Planetary Program. Mars as Viewed by Mariner 9. NASA, 1976.

Viking Lander Imaging Team. The Martian Landscape. NASA, 1978.

Wilford, John Noble. Mars Beckons. Knopf, 1990.


Destination Space. National Geographic Videos, 2000.

Gonzales, Laurence and James Vlahos. “Mars: An Adventurer’s Guide,” National Geographic Adventure (Sept./Oct. 2000) 120-126, 128, 159-161.

Newman, Aline Alexander and David B. Mattingly. “Destination: Mars,” National Geographic World (Jan. 2000) 14-18.

Long, Michael E. “Mars on Earth,” National Geographic (July 1999) 34-51.

Raeburn, Paul. Mars: Uncovering the Secrets of the Red Planet. National Geographic Books, 1998.

Skurzynski, Gloria. Discover Mars. National Geographic Books, 1998.

Rathbun, Elizabeth. Exploring Your Solar System. National Geographic Books, 1989.

Collins, Michael. “Mission to Mars,” National Geographic (Nov. 1988) 733-764.

“Mission to Mars,” National Geographic World (Jan. 1987) 27-31.

Weaver, Kenneth F. “Journey to Mars,” National Geographic (Feb. 1973) 231-263.


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