Studies doubt Mars Ocean theory

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A pair of newly released studies have challenged the theory that a salty sea once lapped the shores of Mars' Meridiani Planum.

The search for water on Earth's barren neighbor is at the crux of the ongoing debate over the likelihood that life may have once existed on the red planet.

In March 2004, NASA's Mars Exploration Rover team, led by principal investigator Steve Squyres, held a press conference to announce that the Opportunity Rover, which was then four months into a comprehensive study of bedrock formations at Meridiani, had discovered geological evidence that the area had once been covered by water.

The team pointed to the presence of a type of sandstone that they believe was formed in the distant past when volcanic rocks were steeped in acidic, salty water that later evaporated. The announcement generated headlines at the time amid suggestions that such a sea could have been home to living organisms, perhaps similar to bacteria or other microbes here on Earth.

"This was an inhabitable environment on Mars. This was a shallow sea," Squyres said in 2004. "These rocks ... it's a salt flat. These are the kinds of environments that are very suitable for life."

Now two new papers based on the same data from Opportunity and published in this week's edition of the journal Nature suggest different explanations for the formations, and cast doubt on the idea that conditions there could have been hospitable to any sort of life.

One paper, authored by Thomas McCollum and Bryan Hynek at the University of Colorado, suggests a massive volcanic eruption at Meridiani laid down the ash sediments that formed the bedrock. The other, written at Arizona State University by Paul Knauth and colleagues, proposes that a meteorite impact could have formed the rock structures.

In both cases, the environment at Meridiani when the rocks were formed would have been sufficiently hot and dry to make it a poor place to support life. And in both cases, the authors believe, their interpretations are simpler and provide a more straightforward explanation for how the rock formations came to be than the theory put forth by the NASA team.

So which of the three theories is correct? Neither McCollum nor Knauth would say that he knows for sure that he's right and the others are wrong, though each believes his theory to be the best.

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