Two strategies of the US space agency NASA may at last have paid off. A ‘better, faster, cheaper’ mission that also uses the ‘follow the water’ approach to Mars exploration has turned up what look like gullies freshly sculpted by water on frigid martian slopes where no liquid water should be.

Water mark? Images from the Mars Global Surveyor appear to show gullies cutting through sand dunes. Credit: NASA/JPL/MSSS

At a news conference called hastily in Washington last week after word leaked out of a paper in the 30 June issue of Science, a team of planetary geologists studying images from the Mars Global Surveyor displayed sharp aerial photographs of red-rock washes and winding channels on the planet (see right). These features are strikingly reminiscent of deserts in the American southwest.

In some cases, the gullies cut through or blanket modern martian features such as sand dunes, suggesting that they formed very recently. If the photos shown had been of Earth instead of Mars, the scientists said, there would have been no doubt that water had carved the features.

“There's still a finite chance that they were formed some other way,” said Michael Malin, head of Malin Space Science Systems, Inc., which built and operates the eagle-eyed camera aboard the Mars Global Surveyor. “But there's a high probability that they were formed by water.”

In one fell swoop, the revelation has established compelling new scientific targets and generated renewed enthusiasm for what had become a rudderless NASA Mars programme beset by the loss late last year of two major missions, the Mars Climate Orbiter and the Mars Polar Lander.

At the same time, it appears to vindicate NASA's ‘follow the water’ strategy for Mars exploration, in which the agency has aimed to investigate the sinuous canyons and possible shorelines that may offer evidence of water in the planet's past, and which may be the best place to look for signs of martian life.

Ed Weiler, NASA associate administrator for space science, was quick to point out that the Mars Global Surveyor had been launched in 1996 under the same ‘better, faster, cheaper’ mandate that was now being blamed for fatal oversights in the navigation of the Mars Climate Orbiter and the design of the Mars Polar Lander.

“I'm just hoping the news today will pass the message that our Mars programme is not dead, in spite of all the rumours of its death a few months ago,” Weiler said last week. “It is very, very pleasing to be talking about something positive for a change.”

NASA must decide by July whether to send an orbiter or a rover to Mars in 2003. Malin, whose stock is sure to rise with these latest revelations, favours an orbiter with an even higher-resolution camera than on the Mars Global Surveyor; others now argue for a rover to follow the water on the ground.

Following the water on Mars may prove much easier than researchers had imagined if water is indeed emerging on the planet's cold, arid surface. Malin and co-worker Kenneth Edgett found about 120 places where water appeared to have gushed from the walls of impact craters, pits and large valleys.

Almost all of these are in the polar regions, usually on slopes shaded from the Sun. This places them in the coldest martian regions of all, where temperatures drop to −100 °C, and where liquid water might seem least likely to appear.

But the two researchers say the cold may actually help by freezing dams of ice in place at the surface. Briny water building up behind the dams might finally burst out in torrents that then scour gullies in the slopes below before quickly vaporizing.

Many gullies end in what the researchers called ‘aprons’ of sediment. These sometimes cover up modern sand dunes and lack impact craters, signs that they are “incredibly new” and may still be forming today, says Edgett.

But not everyone is convinced. Michael Carr of the US Geological Survey, who has spent decades looking for signs of water on Mars but is not part of Malin's team, says that water appears the most ready explanation. He adds that bursts of gas might also lubricate debris flows, and cautions against leaping to earthly conclusions on a different planet, especially one where water would not be expected to persist.

“Water is so difficult to understand, given the physical conditions on the surface of Mars, and we know those physical conditions very, very well—it's just simply too cold,” says Carr. “I'm just having trouble reconciling the observation with the interpretation.”

http://www.msss.com/mars_images/