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Mystery at Gusev Crater

Scientists are curious about an area of soil near the Mars rover that appears to have been peeled away.
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Scientists are puzzled about a patch of soil near the Mars rover Spirit lander that they now call "Magic Carpet." The intrigue has been stirred up by how soil behaved when the lander’s airbags scraped across the martian soil. That soil appears to have been peeled away.

This odd performance of the soil, some speculate, could provide a window into the existence of subsurface water and, maybe, clues about whether Mars could sustain life.

There’s one thing for sure. Whatever the lander’s airbags have caused, the result is a "spirited" debate.

Airbag retraction
Wrapped in protective airbags, the Spirit rover came to rest within Gusev Crater, bouncing and skimming across the landscape nearly 30 times, eventually rolling to full-stop.

Once the airbags deflated, motors and a rib and cable network worked together to tug on the tough fabric, pulling those bags underneath the lander’s set of petals. Doing so permits the rover to drive off its landing perch onto Mars’ surface.

Early images relayed from Spirit showed a patch of soil near the lander, clearly perturbed by the airbag retraction activity.

That small area of martian landscape was later labeled Magic Carpet for how it behaved when scraped by a deflated and then retracting airbag.

Magic carpet ride
"It has been detached and folded like a piece of carpet sliding across the floor," said Mars Exploration Rover science-team member John Grotzinger of Massachusetts Institute of Technology in Cambridge.

Rocks were also dragged by the airbags, leaving impressions and "bow waves" in the soil, Grotzinger reported during a press gathering here at the Jet Propulsion Laboratory (JPL).

"We don't understand it…we're dying to get a close-up look," said Steve Squyres, principal investigator for Spirit's Athena package of scientific tools. He was early in his view that the airbags have uncovered "bizarre" subsurface material. The "weird stuff", Squyres said, appears to be "strangely cohesive."

Spirit scientists had been repeatedly pressed on whether the cohesive nature of the disturbed soil may be water-related — a mud, in fact. So far, that idea doesn’t appear to hold, well what else to say — water.

Super-fine particles clumped together under the influence of the martian environment could act in the manner that’s being seen, suggest Spirit investigators.

Wheel action
Initially, Spirit’s mission planners indicated interest in driving the rover over to this site to look for additional clues about the composition of the martian soil. Those plans seem to have been nixed, however, by cautious rover engineers anxious to avoid getting snagged by lander hardware.

It is within the Spirit rover’s ability, however, to use its wheels to trench the martian terrain. An array of science gear toted by the robot can then be focused on the result of wheel action.

When Spirit rolled off its lander pedestal, it was quickly noted that the rover’s wheels had begun to be caked in martian surface material.

Sand and brine?
"I think we’re seeing, already, preliminary evidence for a variety of materials, just within the soil," said David Des Marais, an astrobiologist from NASA’s Ames Research Center. He is also a lead member of the long-term planning group that is charting future use of the Mars rovers, Spirit and the yet-to-land Opportunity.

Finer grain material is seemingly globally uniform on Mars, Des Marais told . But then more coarse material is available locally too, he said.

"That darker stuff that’s beneath the fines is a step in that direction. This funny peeling that’s occurred, he added, could be, as hypothesized, the result of very fine grain material.

"But another thing that could do something like that, in my opinion, is a mixture of sand and brine," Des Marais explained.

Gully connection
Brines on Mars have been part of the debate regarding gully formation on the planet, now documented to exist at numbers of locations on Mars. Some experts suggest they are the result of water action.

Research suggests that some brines could be sort of fluid-like down to temperatures way below zero, Des Marais said. At Gusev crater, he added, temperatures are such that very concentrated brine could be what is now being tagged as Magic Carpet.

"We can’t go there with the rover. Engineers have an exclusion zone because it’s a navigation hazard. That area is too close to the lander, unfortunately," Des Marais said. "There is a general sense of the group that this type of deposit might not be everywhere. But it certainly has got to be elsewhere," he noted.

With Earth at one end and a very dry place at the other end, Mars is somewhere in-between. The ratio of water to rock material is a scientific objective of the Mars Exploration Rovers.

"These very concentrated brines could be one example of that intermediate domain, such as you might see in deserts…places like Death Valley in California where water is limited - but it is there," Des Marais said.

If indeed if Magic Carpet is brine, this material could be processed to get water out of it — a resource that could help sustain a future human expedition to the red planet, Des Marais concluded.

Mars muck
"What I really see is mud," suggests Gilbert Levin, a former Mars Viking life detection experimenter in the 1970s. He is now Executive Officer for Science at Spherix Incorporated in Beltsville, Maryland.

Levin said that the formation of liquid water can happen under the environmental conditions of Mars. Indeed, that water can even exist in liquid form on the surface of the red planet.

Furthermore, the detection by NASA’s Mars Odyssey of the widespread presence of near-surface ice means liquid water is on the martian surface, Levin told via email.

"Liquid water is generally acknowledged to be necessary for the presence of life on Mars," Levin said, hence the importance of addressing the issue that the so-called Magic Carpet has raised on Mars, he said.

Levin added: "If it looks like muck, and it puddles like muck, and it tracks like muck — it must be muck."