Study: That's Dust, Not Water on Mars

May 8, 2003 -- The prospect of a moist Mars fostering primitive life forms has excited scientific interest in exploration of the Red Planet. But a new, rival theory has emerged that tries to undermine evidence of water and leave the idea of a wet planet literally in the dust.

The Mars Global Surveyor first relayed images showing clear evidence of recently carved gullies on Mars three years ago. Since then more than 10,000 sites of mysteriously streaked gullies have been sighted.

Some have argued the patterns are the sinuous, meandering path of running water that bubbled up from beneath the planet's crust.

Others say liquid carbon dioxide bursting from the Martian crust may have formed them while still others propose that meltwater seeping from vast ice fields carved the gullies.

Now, a somewhat unpopular idea suggests the gullies are the result of nothing but wind and dry sand and silt.

The theory was proposed just over a month before NASA and European space agencies plan to launch probes to Mars that will investigate minerals on the planet and seek possible signs of life — life that most believe would depend on the presence of liquid water.

"The business of finding water on Mars has some political significance now," said Allan Treiman of the Lunar and Planetary Institute in Houston, Texas, who authored the study in the most recent issue of the Journal of Geophysical Research. "So my idea becomes unattractive."

First Glimpses

Michael Malin, principal investigator for the Mars Orbiter Camera on the Mars Global Surveyer spacecraft, was among the first to suggest in 2000 that water flows on the planet. Since scientists believe liquid water is necessary to support life, the discovery raised the exciting possibility that life exists, or recently existed on the planet.

There is little doubt that Mars was once a much wetter place some 3.5 billion years ago. High-resolution pictures of the planet show evidence for sedimentary rocks laid down by ancient lakes and shallow seas. There also appear to be ancient river valley networks snaking throughout the planet.

But controversey remains over whether water existed more recently, or perhaps still exists on the planet. The gullies and what formed them are the focus of this debate.

Return to Mars

NASA plans to launch two probes to Mars this June in what will be the agency's first effort to land a robot on the planet since a failed 1999 mission to deliver the Mars Polar Lander. Engineers lost contact with the Lander just 12 minutes shy of its scheduled touchdown.

This time, assuming the two landers reach Mars safely, the probes should be able to relay clues about the site of an ancient lake and another area where minerals suggest water may have been sloshing billions of years ago.

The European space agency is also launching a probe to Mars, the Mars Express orbiter, in early June.

But it's unlikely that any of the probes will be able to resolve the debate over the Mars gullies, which were carved more recently. Still, water remains a key focus of the NASA project.

Ancient Water

"This mission is all about historical water," said James Garvin, NASA's senior Mars scientist at the agency's headquarters in Washington, D.C. "It may not be until the next mission in '09 that we're able to learn more about the gullies."

There is still a lot to learn about possible ancient water sites, he points out. For example, many believe Mars once had the atmosphere and warmer temperatures to support an Earth-like environment billions of years ago. But Brian Toon of the University of Colorado at Boulder believes Mars' ancient water was the result of catastrophic asteroid strikes. He suggests the water did not linger long on the planet.

By analyzing minerals at the sites of ancient lakes, the probes might help settle that debate.

But, Garvin explains, more time is needed to develop complicated hardware that can land and probe the hilly regions of Mars where gullies have been sighted. In the meantime, theories about the gullies abound.

As Treiman says, "With so little data, you can theorize just about anything."

Blown by the Wind

To determine the gullies are nothing but patterns left behind by dry sandstorms, Treiman compared the Mars images with pictures taken of avalanches. He explains the snow trails in avalanches is the closest comparison he could find to what he believes are dusty gullies on Mars.

"Earth has so much water that you don't get huge accumulations of silt. When you do, it rains and they cement together," he said.

Both, he says, feature raised sides, although the levies on Mars average heights of more than a half mile and those on most avalanche trails are about 200 meters in height.

Still, he argues the scattering of the gullies and their steep slopes are consistent with wind circulation patterns on the planet. He also suggests that the piles of what appear to be rocks at the base of many of these gullies are not rocks washed down by streams of water, but clumps of dust swirled down by wind.

His idea clashes with other new work by researchers at the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder, who determined water from shallow aquifers created the gullies.

Water, Snow and Magma

Jennifer Heldmann and Michael Mellon studied the Mars images and sided with earlier arguments that reservoirs of water, some 660 to 985 feet beneath Mars' surface, are the source of liquid water that shaped the gullies.

Even though cold temperatures and low atmospheric pressure on Mars' surface can't support liquid water, they say the depth of the aquifer, temperatures and pressure all match to permit liquid water to exist just beneath the surface.

Philip Christensen of Arizona State University in Tempe has suggested that dense layers of snow provided the insulation needed to form liquid water.

"There was a layer of snow that once covered everything," said Christensen, who is principle investigator for the Mars Odyssey, an orbiter that has been snapping detailed images of the planet from space. "The snow acted a little like a greenhouse as sunlight penetrates, it is absorbed and melts the snow."

Another theory by Kenneth L. Tanaka and colleagues at the U.S. Geological Survey in Flagstaff, Ariz., suggests that liquid carbon dioxide is behind at least one gully formation. They argue the Martian crust was heated when magma rose to the surface. As liquid carbon dioxide in the crust heated, it expanded, until pressure of overlying material triggered an explosive eruption.

So who's right? NASA's Garvin says, in fact, everyone may be.

"There are more than 10,000 gully systems on Mars. Any one theory to explain the gullies won't work," he said. No one can know for sure until machines, or even better, people are able to search for the answers in Mars' terrain.

"We're going to look at Mars' rocks," Garvin says, "and rocks do not deceive."