Life would have been rough on ancient Mars

Alan Boyle Science editor • Profile • E-mail

NASA's Opportunity rover has found evidence that its landing site in Mars' Meridiani Planum region was once covered with salty water — but could that ancient environment have given rise to life? Probably not, the rover team reported Tuesday, but if life arose elsewhere on the planet, it might have been able to survive there.

The latest conclusions are based on a thoroughgoing analysis of Martian rock layers at Endurance Crater, as well as an earthly simulation that produced the same sorts of minerals seen on the Red Planet. Researchers determined that in ancient times, the soil at the Meridiani Planum site was acidic, oxidizing and sometimes wet — conditions that would probably pose stiff challenges to life as we know it.

"Life that had evolved in other places or earlier times on Mars — if any did — might adapt to Meridiani conditions, but the kind of chemical reactions we think were important to giving rise to life on Earth simply could not have happened at Meridiani," said Harvard University's Andrew Knoll, a member of the rover science team and a co-author of research appearing in Wednesday's issue of the journal Earth and Planetary Science Letters.

In the issue, nine papers by 60 researchers discuss what Meridiani Planum was like eons ago, and provide comparisons to harsh habitats on Earth. The rover team's principal investigator, Steve Squyres, told MSNBC.com that the papers represented the best effort to date to put everything Opportunity has learned into perspective.

"Until this set of papers, all that we had written about the rocks at Meridiani was contained in one four-page paper that came out a year and a half ago," he said. "What we wanted to do was, in a peer-reviewed journal where we had no page limit, sit down and tell the story really well."

Squyres said the researchers looked at extreme environments on Earth — such as salt flats and acidic rivers — to size up the chances for life on ancient Mars under similar conditions.

"You can go to environments on Earth that are arid, oxidizing and acidic, and are full of life," he explained. "The question is the chemistry. ... Getting the kind of biochemistry going to initiate life at that high acidity level could be tough."

The newly published research builds on findings from the first months of Opportunity's mission. The rover landed on Mars in January 2004 — three weeks after its twin, Spirit, touched down on the opposite side of the planet. The $820 million twin-rover mission was originally slated to last only 90 Martian days, or sols, but Spirit is still going strong after a full Martian year, and Opportunity is due to pass that milestone on Dec. 12.

"Each day we cross our fingers and pray that they're going to keep going, because they could drop dead at any time," Squyres said. "But they're pretty tough machines."

Martian analysis
The heart of the latest research is the analysis of a 23-foot-thick (7-meter-thick) stack of rock layers exposed inside Endurance Crater, which is about a half-mile (750 meters) away from Opportunity's landing site. The rover spent six months inside the crater's rim, from June to December 2004.

"This whole story only becomes clear if your rover lasts for hundreds of sols, and you're able to find a great big hole in the ground, and you have engineers who are smart enough to get you down that slope and enable you to sample all that stratigraphy," Squyres said.

Scientists found three divisions within the Endurance rock stack:

• The lowest, oldest portion had the signature of dry sand dunes.
• The middle portion had windblown sheets of sand. Particles in those two layers were produced in part by previous evaporation of liquid water.
• The upper portion, with some layers deposited by flowing water, corresponded to the layers of rock that Opportunity had found in the shallower crater where it first came to rest.

Materials in all three divisions were wet both before and after the layers were deposited by either wind or water, the researchers said. They described chemical evidence that the sand grains deposited in the layers had been altered by water before the layers formed. Scientists analyzed how acidic water moving through the layers after they were in place caused changes such as the formation within the rocks of hematite-rich spherules informally known as blueberries.

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