Volume: 04, Issue: 07 11/30/2005 
Opportunity captured this view of Burns Cliff after driving right to the base of this southeastern portion of the inner wall of Endurance Crater. Image courtesy NASA/JPL-Caltech/Cornell.
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Spirit used its panoramic camera to obtain this view of the impact feature called East Basin to the northeast of Husband Hill. Image courtesy NASA/JPL-Caltech/Cornell.
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Opportunity captures image of a large wind-blown ripple called Scylla and other nearby ripples and patches of brighter rock strewn with dark cobbles. Image courtesy NASA/JPL-Caltech/Cornell.
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Spirit descends from Columbia Hills. Image courtesy NASA/JPL-Caltech/NMMNH.
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Other Articles in This Issue:
ESA Spacecraft Makes Intriguing New Discoveries
Venus Express Observes Earth, Moon
Mars Reconnaissance Orbiter Passes Halfway Mark
Chat about Spaceflight with a NASA Astronaut

Mars Rovers Celebrate Anniversary, Explore Possibility of Life

As NASA’s Mars Exploration Rover Spirit was celebrating its one-Martian-year anniversary on the Red Planet Nov. 20, 2005, its twin, Opportunity, was preparing for its similar anniversary on Dec. 12 by making new discoveries about the possibility of life on the planet. According to Opportunity’s new findings, life may have had a tough time getting started in the ancient environment of Mars.

Mars Exploration Rover principal investigator Dr. Steve Squires of Cornell University and his team recently released what Squires calls “the most significant set of papers [the] team has published." The new detailed reports deduce that conditions in the Meridiani Planum region of Mars were strongly acidic, oxidizing, and sometimes wet. Those conditions probably posed stiff challenges to the potential origin of Martian life.

Based on Opportunity's data, nine papers by 60 researchers in volume 240, issue 1 of the journal Earth and Planetary Science Letters discuss what this part of the Martian Meridiani Planum region was like eons ago. The papers present comparisons to some harsh habitats on Earth and examine the ramifications for possible life on Mars.

According to Dr. Andrew Knoll of Harvard University, a co-author of the paper, "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."

Scientists analyzed data about stacked sedimentary rock layers 23 feet thick, exposed inside Endurance Crater. They identified three divisions within the 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 layers Opportunity found earlier inside a smaller crater near its landing site.

Materials in all three divisions were wet both before and after the layers were deposited by either wind or water. Researchers 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 of hematite-rich spherules within the rocks.

Experimental and theoretical testing reinforces the interpretation of changes caused by acidic water interacting with the rock layers.

"We made simulated Mars rocks in our laboratory, then infused acidic fluids through them," said researcher Nicholas Tosca from the State University of New York, Stony Brook. "Our theoretical model shows the minerals predicted to form when those fluids evaporate bear a remarkable similarity to the minerals identified in the Meridiani outcrop."

The stack of layers in Endurance Crater resulted from a changeable environment perhaps 3.5 to 4 billion years ago. The area may have looked like salt flats occasionally holding water, surrounded by dunes. The White Sands region in New Mexico bears a similar physical resemblance. For the chemistry and mineralogy of the environment, an acidic river basin named Rio Tinto, in Spain, provides useful similarities, said Dr. David Fernandez-Remolar of Spain's Centro de Astrobiologia and co-authors.

Many types of microbes live in the Rio Tinto environment, one of the reasons for concluding that ancient Meridiani could have been habitable. However, the organisms at Rio Tinto are descended from populations that live in less acidic and stressful habitats. If Meridiani had any life, it might have had to originate in a different habitat.

"You need to be very careful when you are talking about the prospect for life on Mars," Knoll said. "We've looked at only a very small parcel of Martian real estate. The geological record Opportunity has examined comes from a relatively short period out of Mars' long history."

Images and information about the rovers and their discoveries are available at the following website:

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