Mars water theory disputed

Jim Erickson, Rocky Mountain News

Published December 22, 2005 at midnight

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Two Boulder scientists are challenging the widely held view that NASA's durable Mars rovers found strong evidence that the planet once held long-standing pools of briny water that could have supported primitive life.

Instead, University of Colorado planetary scientists Thomas McCollom and Brian Hynek envision a hellish place where volcanic ash and jets of sulfurous steam - possibly hotter than 200 degrees - formed the distinctive layered rock outcrops found by the six-wheeled Opportunity rover.

"We think it was far less favorable for past biological activity than other scenarios that have been proposed," McCollom said.

But the lead scientist on the Mars Exploration Rover (MER) mission dismissed the CU idea as misguided and uninformed.

Cornell University's Steve Squyres said the Boulder scientists did not have access to reams of recent Opportunity data, all of which "really solidify the case that water was involved in a very substantial way at this place."

McCollom and Hynek make their case in an article in today's edition of the journal Nature. A second Nature paper, by L. Paul -Knauth of Arizona State University, suggests the same sandstone deposits resulted from a meteorite impact.

The twin rovers, Spirit and Opportunity, landed on opposite sides of Mars in January 2004. Originally designed to last three months, both rovers remain operational after nearly two years.

Their mission: to search for evidence that the now-arid planet once harbored water that may have allowed primitive life to gain a foothold billions of years ago.

Opportunity bounced onto the surface of Meridiani Planum, a vast plain that straddles the planet's equator. Three months after it arrived, Squyres declared at a news conference that Meridiani rocks spoke of an ancient Mars that once held salty pools capable of supporting life.

The shallow pools would come and go, according to the scenario painted by MER team scientists. When the pools evaporated, they left behind salt deposits that combined with windblown volcanic dust to form dunes.

Groundwater later altered the chemical composition of the dune minerals, which eventually hardened into the buff-colored rocks that Opportunity explored.

U.S. Geological Survey planetary scientist Michael Carr, author of the book Water on Mars, said the explanation proposed by McCollom and Hynek "is possible, but I don't think it's as likely as the MER model."

In the scenario outlined by the CU researchers, volcanic eruptions belched ash flows that blanketed Meridiani several billion years ago. The ash solidified into rock.

Later, sulfurous steam worked its way up through cracks in the rock. Sulfuric acid formed and altered the rock to create its current chemical composition.

Some of the acidic steam may have vented at the surface, forming smelly jets like the fumaroles of Yellowstone National Park.

"If McCollom and Hynek's scenario for the formation of the Meridiani deposits is correct, the origin and modification of these sediments would have occurred at high temperature with little groundwater (and no surface water), greatly reducing the possibility that these rocks indicate that a habitable environment ever existed at Meridiani," Boulder planetary scientist Mark Bullock wrote in a commentary that accompanies the Nature research papers.

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