Other Work

A Mars Never Dreamed Of
By Kathy Sawyer
National Geographic | Feb. 2001, p. 30

(SEE THE FULL STORY: http://www.nationalgeographic.com/ngm/0102/feature2/index.html)


Mars has been born afresh in the human mind with each exploratory thrust. Now it was happening again under the astonished gaze of Ken Edgett as he sat at his computer, tucked away in a leafy industrial park in the Pacific coast hills outside San Diego. One of Edgett’s tasks, unique on Earth at the moment, was to inspect virtually every one of the thousands of images raining in at the rate of 5,000 pixels per second from the only operational spacecraft in the vicinity of the red planet—the Mars Global Surveyor (MGS). For a little while each day, in some sense, the young geologist had this hatchling Mars all to himself. . . Although he had spent many of his 34 years honing his own sense of the place—as if he had scaled its Everest-dwarfing heights, slogged across its frosty dunes, felt the sting of its dust storms, and shaken its fine sand out of his boots—he confessed this Mars shocked even him. . .

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.

[Edgett’s boss, geomorphologist Michael] 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. . .