Saltwater evidence detected on Mars

NASA rover finds signs that water once flowed deep enough to swim in

`A habitable environment'

March 24, 2004|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

WASHINGTON - NASA's rover Opportunity has found convincing evidence that the rocks near its landing site on Mars were laid down by salty water deep enough to swim in, scientists announced yesterday.

It is not clear yet whether this was the edge of a Martian sea, or the shores of a water-filled desert basin. But "this was a habitable environment on Mars," said Steven Squyres, principal investigator on the $820 million planetary mission.

The search for evidence that life once swam in these waters will have to await the arrival of future probes, scientists said. But sedimentary rocks are just what they would have ordered to preserve the evidence of that life.

"If you're into the search for fossils on Mars, this is the place to go," said Ed Weiler, the National Aeronautics and Space Administration's associate administrator for space science.

Engineers at NASA's Jet Propulsion Laboratory used photographs from Opportunity's microscopic imager to assemble a mosaic of 152 pictures of the bedrock that rims "Eagle Crater," where the rover landed. The composite revealed curved layers of sediment preserved in the rocks identical to those formed on Earth by rippling at the bottom of bodies of flowing water.

"We feel very confident this adds up to ripples moving in water," said John Grotzinger of the Massachusetts Institute of Technology, a co-investigator on the mission. Based on the size of the ripples, he estimated the flow rate at about 6 inches per second.

Scientists said they don't know how widespread or deep the water was, how long it flowed before drying up, how warm it was or even how long ago it disappeared. But they have dispatched Opportunity to Endurance Crater, about 765 yards away, where orbital photos suggest more of the same type of rocks might lie exposed.

En route, scientists hope that Opportunity will begin to measure the horizontal extent of the vanished lake or sea that formed the rocks. When it arrives at the crater a month or more from now, they expect to find bedrock exposures 10 or 20 yards deep. That would reveal a deeper slice of the area's geological history, and more clues to the history of water there.

Opportunity landed on Mars on Jan. 25, three weeks after its twin, Spirit, bounced down in Gusev Crater, on the other side of the planet.

In a sort of interplanetary hole-in-one, Opportunity rolled on impact across a flat, barren plain and into a shallow crater no bigger than a small movie theater. When the first pictures came back, mission scientists were delighted to find the crater was rimmed by an outcrop of bedrock waiting to be examined by the rover's kit of cameras and spectrographic instruments.

They kept the rover there more than eight weeks, commanding it to roll back and forth along the outcrop, taking pictures, doing spectrographic analyses of the minerals, grinding away at the rocks and sending data back to eager scientists on Earth.

Resolving longstanding speculation about water on Mars has been one of NASA's goals for decades. Orbital photos since the 1970s have revealed land forms that appeared to be river valleys, water-carved canyons and shorelines, leading scientists to believe Mars once supported a climate far warmer and wetter than the cold, desert planet we see today.

Learning more about the history of water on Mars, and where it has gone holds the key to the mystery of whether life could ever have evolved there. It may also reveal what happened to the planet's climate, and whether Mars still holds enough water near the surface to supply humans if they seek to establish a permanent presence there.

Three weeks ago, mission scientists announced that Opportunity had found evidence that the rocks had once been soaked in salty and acidic water. But they described it as ground water - the kind you have to pump from the ground.

But they hinted then that they knew more than they were ready to talk about.

Because of the potential importance of their discovery, they decided to submit their evidence for a peer review by six "outside" scientists unconnected to the Mars mission. Those scientists have now concluded that Opportunity has almost certainly found evidence of flowing water on Mars.

"I think the evidence the [NASA] team put together is the best explanation for these rocks," said Dave Rubin, a sedimentologist with the U.S. Geological Survey and a member of the peer review panel. "I was astonished. They're on Mars, and we're seeing sedimentary structures just like we see on Earth."

Sedimentation in still water produces flat, parallel layers of sediment that later harden into rock. Some of the layering Opportunity found is flat. But sediments deposited by flowing water are piled into ripples that leave little, smilelike curves in cross-sections of the rocks. Those show up clearly in other parts of the outcrop photographed by the Mars rover.

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