Rover finds evidence water once flowed on Red Planet

By Guy Gugliotta
The Washington Post

	AP This is an image of the Mars rock dubbed "El Capitan," which scientists concluded was once wet.
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For several days late last month Opportunity probed, drilled and analyzed a stone outcrop in Mars' Meridiani Planum, finding geological features and mineralogical characteristics that are common on Earth in rock that has either been leached by groundwater or formed from sediment laid down in a lake or pond.

"The puzzle pieces have been falling into place, and the last puzzle piece fell into place a few days ago," said Cornell University astronomer Steve Squyres, principal investigator of NASA's Mars Exploration Rover mission. "We have concluded that the rocks here were once soaked in liquid water." Squyres, speaking at a news conference at the headquarters of the National Aeronautics and Space Administration, said the Mars rover team did not know how long, or how long ago, the water had been in Meridiani Planum, or whether it had been on the surface or underground.

Scientists have long observed signs of possible long-ago water erosion on Mars and of water ice at its poles, but the one-time presence of liquid water marked a crucial milepost in the search for life on a planet that today is largely a bleak and inhospitable desert. Opportunity, and its twin, Spirit, which is exploring a rocky plain on the planet's other side, were sent to Mars specifically to determine whether liquid water had been present long enough to allow life to evolve.

Opportunity might have found the answer: "What's the significance?" Squyres said. "We believe that for some period of time, (Meridiani Planum) was a habitable environment, suitable for life. That doesn't mean that life was there." The answer to that question, the NASA team said, would likely have to wait for a later mission. Benton C. Clark III, a Lockheed Martin Space Systems scientist and a member of the rover team, said the rovers' instruments were designed to analyze minerals, not search for fossils or the organic, carbon-containing compounds that indicate life.

Opportunity, a 384-pound, golf cart-sized robot, landed on Mars on Jan. 24 in a shallow crater at the planet's equator, three weeks after Spirit touched down in what is thought to be an ancient lakebed 6,600 miles away.

The two rovers are designed for 90 days of exploration. Both are operating well, and project scientist Joy Crisp, of NASA, said there is no reason they could not keep working for nine months, or longer. "We cannot predict when the missions will end," she said.

Since Opportunity's landing, Squyres said "every single part of our payload" had "been brought to bear" on moving the six-wheeled Opportunity about 30 feet to the outcrop dubbed "El Capitan," for the famous cliff in Yosemite National Park. The martian outcrop is a 10-inch high rock shelf about 65 feet long whose chief attraction was that it showed evidence of "layering," indicating it may have been laid down long ago as sediment.

Once it navigated to the rock face, Opportunity performed several days of photography, spectrographic analysis and coring with a special drill, gathering and transmitting a body of evidence that enabled the team to reach the consensus that El Capitan had been wet for a long time: "I think each of us had our own set of prejudices," Squyres said. "All of us have come to believe it."

Opportunity's spectrographic instruments found elevated concentrations of sulfur in the rock, growing stronger as drills went deeper into the stone face. Clark said this likely indicated the presence of sulfate salts, a telltale sign of liquid water.

"The only way you can form such large concentrations of salt is dissolve it in water and allow the water to evaporate," Clark said. Also found was an iron sulfate mineral called jarosite, which Squyres said can be formed only in the presence of water.
 
Meanwhile, microscopic photography showed "vugs" in the stone, tiny grooves that look as if the edge of a coin had been stabbed into it and then removed. Team member John Grotzinger, a Massachusetts Institute of Technology geologist, described this as a common feature in briny sediments when salt crystals formed in the stone are subsequently eroded away or dissolved.

Grotzinger also said the team also found "crossbedding" — layers of rock that lie at an angle to other layers, indicating formation by wind or water currents. In addition, the team found BB-sized gray spheres that the members dubbed "blueberries," possible evidence of minerals coming out of solution in porous, water-soaked rock. Grotzinger urged caution in interpreting these findings, however, noting that similar appearing characteristics can be found in volcanic deposits.

Squyres said the team had no way to tell how long water had been at Meridiani Planum or how long ago. He also said the evidence did not show whether liquid water had been present on the surface of Mars, or whether it was groundwater that had permeated the El Capitan stone and before it was uplifted by some long-ago geological event. With Opportunity headed for other outcrops, however, Squyres suggested that the team might soon be able to shed further light on the question.

"Stay tuned," he said.

Information from The Associated Press is included in this report.

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