Bizarre Mars Mountain Possibly Built by Wind, Not Water

Mike Wall
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In this image released by NASA on Monday, Aug. 27, 2012, a photo taken by the Mast Camera (MastCam) highlights the geology of Mount Sharp, a mountain inside Gale Crater, where the rover landed. Prior to the rover's landing on Mars, observations from orbiting satellites indicated that the lower reaches of Mount Sharp, below the line of white dots, are composed of relatively flat-lying strata that bear hydrated minerals. Those orbiter observations did not reveal hydrated minerals in the higher, overlying strata. The MastCam data now reveal a strong discontinuity in the strata above and below the line of white dots, agreeing with the data from orbit. Strata overlying the line of white dots are highly inclined (dipping from left to right) relative to lower, underlying strata. The inclination of these strata above the line of white dots is not obvious from orbit. This provides independent evidence that the absence of hydrated minerals on the upper reaches of Mount Sharp may coincide with a very different formation environment than lower on the slopes. The train of white dots may represent an "unconformity," or an area where the process of sedimentation stopped. (AP Photo/NASA/JPL-Caltech/MSSS)

The mysterious Martian mountain that beckons NASA's Curiosity rover was likely built primarily by wind rather than water, as previously believed, a new study suggests.

Many scientists suspect that the 3.4-mile-high (5.5 kilometers) Mount Sharp formed primarily from layers of lakebed silt, which is one of the main reasons that the mountain was selected as Curiosity's ultimate destination. But the new study holds that wind probably did most of the heavy lifting.

"Our work doesn't preclude the existence of lakes in Gale Crater, but suggests that the bulk of the material in Mount Sharp was deposited largely by the wind," study co-author Kevin Lewis, of Princeton University, said in a statement. [Latest Mars Photos from Curiosity]

A mysterious mountain

The Curiosity rover landed inside 96-mile-wide (154 km) Gale Crater last August, kicking off a two-year surface mission to investigate Mars' past and present potential to host microbial life.

The 1-ton robot has already checked off its main goal, finding that a spot near its landing site called Yellowknife Bay was once capable of supporting life billions of years ago. But the mission team is still gearing up to send Curiosity on a 6-mile (10 km) trek to the base of Mount Sharp, which was identified before launch as the rover's main science target.

Observations from NASA's Mars Reconnaissance Orbiter (MRO) suggest that Mount Sharp's foothills were exposed to liquid water long ago. And as Curiosity climbs up through the mound's many layers, the rover will be able to read the Red Planet's environmental history like a book, mission scientists reasoned.

In the new study, researchers used other MRO observations to devise a new theory of Mount Sharp's formation. The team determined that the mound's layers aren't flat-lying stacks, as would be expected in lakebed deposits. Rather, they fan outward in an odd radial pattern from Mount Sharp's center, researchers said.

This finding is consistent with results from the team's computer model, which suggested that wind blowing down Gale's slopes could build a mound in the crater's center while leaving areas near the rim relatively bare.

So Mount Sharp may not be the eroded remnant of an even bigger mound that once filled Gale from rim to rim.

"Every day and night you have these strong winds that flow up and down the steep topographic slopes. It turns out that a mound like this would be a natural thing to form in a crater like Gale," said Lewis, who is a participating scientist on Curiosity's mission. "Contrary to our expectations, Mount Sharp could have essentially formed as a free-standing pile of sediment that never filled the crater."

Testing the theory

Curiosity team member Dawn Sumner, who was not involved in the new study, said it presented interesting ideas that the rover should be able to test out in the future.

"This paper provides a new model for Mount Sharp that makes specific predictions about the characteristics of the rocks within the mountain," Sumner, a geology professor at the University of California-Davis, said in a statement. "Observations by Curiosity at the base of Mount Sharp can test the model by looking for evidence of wind deposition of sediment."

However Mount Sharp formed, the huge Mars mountain should be a productive hunting ground for Curiosity, Lewis said.

"One way or another, we're going to get an incredible history book of all the events going on while that sediment was being deposited," he said. "I think Mount Sharp will still provide an incredible story to read. It just might not have been a lake."

The new study was published in the May issue of the journal Geology.

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