Mars Photos May Indicate The Recent Flow of Water

Gullies on a Mars crater wall may have held a recent flow of liquid water, the presence of which would increase the odds of some kind of life on the planet. (Nasa Via Associated Press)

No one knows where the water may have come from, or how much of it could be feeding other gullies on the planet. One theory is that stores of water are being kept warm enough underground to remain in the liquid state, with some of it flowing slowly and steadily through cracks that open into the sides of craters. As water approaches the surface, the thinking goes, it freezes, forming an ice dam. But periodically those dams burst, sending a mini-flood foaming down a slope.

Water would be especially likely to remain in liquid form underground if it were salty or, to an even greater extent, if it were acidic from certain dissolved minerals -- factors that allow water to remain fluid at subfreezing temperatures.

Scientists said they may soon have a chance to test that proposition. That is because the Mars Reconnaissance Orbiter, which began its studies of the planet last month, has a high-resolution, near-infrared camera that can analyze the chemical composition of the new pale sediments.

The orbiter's first priority is to map sites near the icy north pole where NASA's Phoenix lander -- to be launched next August -- is scheduled to touch down in 2008. But after that, Meyer said, he suspects a look at the gullies will be a new high priority.

Other scientists said it would be important to gather more evidence to rule out alternative explanations for the gully changes, including flows of dry granular material or frozen carbon dioxide. But several agreed that they could think of no better explanation than water for what they were seeing.

"I think the evidence for this recent water is compelling," said Philip Christensen, a geoscientist at Arizona State University in Tempe who oversaw one of the global surveyor instruments and is involved in the Mars Exploration Rover missions. "I think today we can honestly talk about liquid water on Mars."

In their report in Science, the team members also described several new craters that appeared during the surveyor mission, again revealed by "before" and "after" photographs. By extrapolating from those data, they conclude that Mars is pocked by about a dozen new craters every year.

That is important, scientists said, because researchers have used the density of craters on planets to estimate the age of surface features by presuming a certain frequency of new impacts.

With the new hard data in hand, they were able to verify that the "crater clock" they have been using is essentially correct -- and that the number of meteorites falling from the Martian sky is not insignificant, said Michael C. Malin, president of Malin Space Science Systems.

"That raises a question: 'Is this a hazard for astronauts that we have to consider?' " Malin said. "The answer," he asserted, "is yes."